File: rfc9325.html

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<!DOCTYPE html>
<html lang="en" class="BCP RFC">
<head>
<meta charset="utf-8">
<meta content="Common,Latin" name="scripts">
<meta content="initial-scale=1.0" name="viewport">
<title>RFC 9325: Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)</title>
<meta content="Yaron Sheffer" name="author">
<meta content="Peter Saint-Andre" name="author">
<meta content="Thomas Fossati" name="author">
<meta content="
       Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are used to protect data exchanged over a wide range of application protocols and can also form the basis for secure transport protocols.  Over the years, the industry has witnessed several serious attacks on TLS and DTLS, including attacks on the most commonly used cipher suites and their modes of operation.  This document provides the latest recommendations for ensuring the security of deployed services that use TLS and DTLS. These recommendations are applicable to the majority of use cases. 
       RFC 7525, an earlier version of the TLS recommendations, was published when the industry was transitioning to TLS 1.2. Years later, this transition is largely complete, and TLS 1.3 is widely available. This document updates the guidance given the new environment and obsoletes RFC 7525. In addition, this document updates RFCs 5288 and 6066 in view of recent attacks. 
    " name="description">
<meta content="xml2rfc 3.15.2" name="generator">
<meta content="9325" name="rfc.number">
<!-- Generator version information:
  xml2rfc 3.15.2
    Python 3.9.14
    appdirs 1.4.4
    ConfigArgParse 1.5.3
    google-i18n-address 2.5.1
    html5lib 1.1
    intervaltree 3.1.0
    Jinja2 3.1.2
    lxml 4.9.0
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    PyYAML 6.0
    requests 2.28.0
    setuptools 44.1.1
    six 1.16.0
    wcwidth 0.2.5
    weasyprint 56.1
-->
<link href="rfc9325.xml" rel="alternate" type="application/rfc+xml">
<link href="#copyright" rel="license">
<style type="text/css">/*

  NOTE: Changes at the bottom of this file overrides some earlier settings.

  Once the style has stabilized and has been adopted as an official RFC style,
  this can be consolidated so that style settings occur only in one place, but
  for now the contents of this file consists first of the initial CSS work as
  provided to the RFC Formatter (xml2rfc) work, followed by itemized and
  commented changes found necessary during the development of the v3
  formatters.

*/

/* fonts */
@import url('https://fonts.googleapis.com/css?family=Noto+Sans'); /* Sans-serif */
@import url('https://fonts.googleapis.com/css?family=Noto+Serif'); /* Serif (print) */
@import url('https://fonts.googleapis.com/css?family=Roboto+Mono'); /* Monospace */

@viewport {
  zoom: 1.0;
  width: extend-to-zoom;
}
@-ms-viewport {
  width: extend-to-zoom;
  zoom: 1.0;
}
/* general and mobile first */
html {
}
body {
  max-width: 90%;
  margin: 1.5em auto;
  color: #222;
  background-color: #fff;
  font-size: 14px;
  font-family: 'Noto Sans', Arial, Helvetica, sans-serif;
  line-height: 1.6;
  scroll-behavior: smooth;
}
.ears {
  display: none;
}

/* headings */
#title, h1, h2, h3, h4, h5, h6 {
  margin: 1em 0 0.5em;
  font-weight: bold;
  line-height: 1.3;
}
#title {
  clear: both;
  border-bottom: 1px solid #ddd;
  margin: 0 0 0.5em 0;
  padding: 1em 0 0.5em;
}
.author {
  padding-bottom: 4px;
}
h1 {
  font-size: 26px;
  margin: 1em 0;
}
h2 {
  font-size: 22px;
  margin-top: -20px;  /* provide offset for in-page anchors */
  padding-top: 33px;
}
h3 {
  font-size: 18px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h4 {
  font-size: 16px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
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h5, h6 {
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}
#n-copyright-notice {
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  padding-bottom: 1em;
  margin-bottom: 1em;
}
/* general structure */
p {
  padding: 0;
  margin: 0 0 1em 0;
  text-align: left;
}
div, span {
  position: relative;
}
div {
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}
.alignRight.art-text {
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  margin-bottom: 1.5em;
}
.alignRight.art-text pre {
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}
.alignRight {
  margin: 1em 0;
}
.alignRight > *:first-child {
  border: none;
  margin: 0;
  float: right;
  clear: both;
}
.alignRight > *:nth-child(2) {
  clear: both;
  display: block;
  border: none;
}
svg {
  display: block;
}
.alignCenter.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignCenter.art-text pre {
  padding: 0;
}
.alignCenter {
  margin: 1em 0;
}
.alignCenter > *:first-child {
  display: table;
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  margin: 0 auto;
}

/* lists */
ol, ul {
  padding: 0;
  margin: 0 0 1em 2em;
}
ol ol, ul ul, ol ul, ul ol {
  margin-left: 1em;
}
li {
  margin: 0 0 0.25em 0;
}
.ulCompact li {
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}
ul.empty, .ulEmpty {
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}
ul.empty li, .ulEmpty li {
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}
ul.ulBare, li.ulBare {
  margin-left: 0em !important;
}
ul.compact, .ulCompact,
ol.compact, .olCompact {
  line-height: 100%;
  margin: 0 0 0 2em;
}

/* definition lists */
dl {
}
dl > dt {
  float: left;
  margin-right: 1em;
}
/* 
dl.nohang > dt {
  float: none;
}
*/
dl > dd {
  margin-bottom: .8em;
  min-height: 1.3em;
}
dl.compact > dd, .dlCompact > dd {
  margin-bottom: 0em;
}
dl > dd > dl {
  margin-top: 0.5em;
  margin-bottom: 0em;
}

/* links */
a {
  text-decoration: none;
}
a[href] {
  color: #22e; /* Arlen: WCAG 2019 */
}
a[href]:hover {
  background-color: #f2f2f2;
}
figcaption a[href],
a[href].selfRef {
  color: #222;
}
/* XXX probably not this:
a.selfRef:hover {
  background-color: transparent;
  cursor: default;
} */

/* Figures */
tt, code, pre {
  background-color: #f9f9f9;
  font-family: 'Roboto Mono', monospace;
}
pre {
  border: 1px solid #eee;
  margin: 0;
  padding: 1em;
}
img {
  max-width: 100%;
}
figure {
  margin: 0;
}
figure blockquote {
  margin: 0.8em 0.4em 0.4em;
}
figcaption {
  font-style: italic;
  margin: 0 0 1em 0;
}
@media screen {
  pre {
    overflow-x: auto;
    max-width: 100%;
    max-width: calc(100% - 22px);
  }
}

/* aside, blockquote */
aside, blockquote {
  margin-left: 0;
  padding: 1.2em 2em;
}
blockquote {
  background-color: #f9f9f9;
  color: #111; /* Arlen: WCAG 2019 */
  border: 1px solid #ddd;
  border-radius: 3px;
  margin: 1em 0;
}
cite {
  display: block;
  text-align: right;
  font-style: italic;
}

/* tables */
table {
  width: 100%;
  margin: 0 0 1em;
  border-collapse: collapse;
  border: 1px solid #eee;
}
th, td {
  text-align: left;
  vertical-align: top;
  padding: 0.5em 0.75em;
}
th {
  text-align: left;
  background-color: #e9e9e9;
}
tr:nth-child(2n+1) > td {
  background-color: #f5f5f5;
}
table caption {
  font-style: italic;
  margin: 0;
  padding: 0;
  text-align: left;
}
table p {
  /* XXX to avoid bottom margin on table row signifiers. If paragraphs should
     be allowed within tables more generally, it would be far better to select on a class. */
  margin: 0;
}

/* pilcrow */
a.pilcrow {
  color: #666; /* Arlen: AHDJ 2019 */
  text-decoration: none;
  visibility: hidden;
  user-select: none;
  -ms-user-select: none;
  -o-user-select:none;
  -moz-user-select: none;
  -khtml-user-select: none;
  -webkit-user-select: none;
  -webkit-touch-callout: none;
}
@media screen {
  aside:hover > a.pilcrow,
  p:hover > a.pilcrow,
  blockquote:hover > a.pilcrow,
  div:hover > a.pilcrow,
  li:hover > a.pilcrow,
  pre:hover > a.pilcrow {
    visibility: visible;
  }
  a.pilcrow:hover {
    background-color: transparent;
  }
}

/* misc */
hr {
  border: 0;
  border-top: 1px solid #eee;
}
.bcp14 {
  font-variant: small-caps;
}

.role {
  font-variant: all-small-caps;
}

/* info block */
#identifiers {
  margin: 0;
  font-size: 0.9em;
}
#identifiers dt {
  width: 3em;
  clear: left;
}
#identifiers dd {
  float: left;
  margin-bottom: 0;
}
/* Fix PDF info block run off issue */
@media print {
  #identifiers dd {
    float: none;
  }
}
#identifiers .authors .author {
  display: inline-block;
  margin-right: 1.5em;
}
#identifiers .authors .org {
  font-style: italic;
}

/* The prepared/rendered info at the very bottom of the page */
.docInfo {
  color: #666; /* Arlen: WCAG 2019 */
  font-size: 0.9em;
  font-style: italic;
  margin-top: 2em;
}
.docInfo .prepared {
  float: left;
}
.docInfo .prepared {
  float: right;
}

/* table of contents */
#toc  {
  padding: 0.75em 0 2em 0;
  margin-bottom: 1em;
}
nav.toc ul {
  margin: 0 0.5em 0 0;
  padding: 0;
  list-style: none;
}
nav.toc li {
  line-height: 1.3em;
  margin: 0.75em 0;
  padding-left: 1.2em;
  text-indent: -1.2em;
}
/* references */
.references dt {
  text-align: right;
  font-weight: bold;
  min-width: 7em;
}
.references dd {
  margin-left: 8em;
  overflow: auto;
}

.refInstance {
  margin-bottom: 1.25em;
}

.references .ascii {
  margin-bottom: 0.25em;
}

/* index */
.index ul {
  margin: 0 0 0 1em;
  padding: 0;
  list-style: none;
}
.index ul ul {
  margin: 0;
}
.index li {
  margin: 0;
  text-indent: -2em;
  padding-left: 2em;
  padding-bottom: 5px;
}
.indexIndex {
  margin: 0.5em 0 1em;
}
.index a {
  font-weight: 700;
}
/* make the index two-column on all but the smallest screens */
@media (min-width: 600px) {
  .index ul {
    -moz-column-count: 2;
    -moz-column-gap: 20px;
  }
  .index ul ul {
    -moz-column-count: 1;
    -moz-column-gap: 0;
  }
}

/* authors */
address.vcard {
  font-style: normal;
  margin: 1em 0;
}

address.vcard .nameRole {
  font-weight: 700;
  margin-left: 0;
}
address.vcard .label {
  font-family: "Noto Sans",Arial,Helvetica,sans-serif;
  margin: 0.5em 0;
}
address.vcard .type {
  display: none;
}
.alternative-contact {
  margin: 1.5em 0 1em;
}
hr.addr {
  border-top: 1px dashed;
  margin: 0;
  color: #ddd;
  max-width: calc(100% - 16px);
}

/* temporary notes */
.rfcEditorRemove::before {
  position: absolute;
  top: 0.2em;
  right: 0.2em;
  padding: 0.2em;
  content: "The RFC Editor will remove this note";
  color: #9e2a00; /* Arlen: WCAG 2019 */
  background-color: #ffd; /* Arlen: WCAG 2019 */
}
.rfcEditorRemove {
  position: relative;
  padding-top: 1.8em;
  background-color: #ffd; /* Arlen: WCAG 2019 */
  border-radius: 3px;
}
.cref {
  background-color: #ffd; /* Arlen: WCAG 2019 */
  padding: 2px 4px;
}
.crefSource {
  font-style: italic;
}
/* alternative layout for smaller screens */
@media screen and (max-width: 1023px) {
  body {
    padding-top: 2em;
  }
  #title {
    padding: 1em 0;
  }
  h1 {
    font-size: 24px;
  }
  h2 {
    font-size: 20px;
    margin-top: -18px;  /* provide offset for in-page anchors */
    padding-top: 38px;
  }
  #identifiers dd {
    max-width: 60%;
  }
  #toc {
    position: fixed;
    z-index: 2;
    top: 0;
    right: 0;
    padding: 0;
    margin: 0;
    background-color: inherit;
    border-bottom: 1px solid #ccc;
  }
  #toc h2 {
    margin: -1px 0 0 0;
    padding: 4px 0 4px 6px;
    padding-right: 1em;
    min-width: 190px;
    font-size: 1.1em;
    text-align: right;
    background-color: #444;
    color: white;
    cursor: pointer;
  }
  #toc h2::before { /* css hamburger */
    float: right;
    position: relative;
    width: 1em;
    height: 1px;
    left: -164px;
    margin: 6px 0 0 0;
    background: white none repeat scroll 0 0;
    box-shadow: 0 4px 0 0 white, 0 8px 0 0 white;
    content: "";
  }
  #toc nav {
    display: none;
    padding: 0.5em 1em 1em;
    overflow: auto;
    height: calc(100vh - 48px);
    border-left: 1px solid #ddd;
  }
}

/* alternative layout for wide screens */
@media screen and (min-width: 1024px) {
  body {
    max-width: 724px;
    margin: 42px auto;
    padding-left: 1.5em;
    padding-right: 29em;
  }
  #toc {
    position: fixed;
    top: 42px;
    right: 42px;
    width: 25%;
    margin: 0;
    padding: 0 1em;
    z-index: 1;
  }
  #toc h2 {
    border-top: none;
    border-bottom: 1px solid #ddd;
    font-size: 1em;
    font-weight: normal;
    margin: 0;
    padding: 0.25em 1em 1em 0;
  }
  #toc nav {
    display: block;
    height: calc(90vh - 84px);
    bottom: 0;
    padding: 0.5em 0 0;
    overflow: auto;
  }
  img { /* future proofing */
    max-width: 100%;
    height: auto;
  }
}

/* pagination */
@media print {
  body {

    width: 100%;
  }
  p {
    orphans: 3;
    widows: 3;
  }
  #n-copyright-notice {
    border-bottom: none;
  }
  #toc, #n-introduction {
    page-break-before: always;
  }
  #toc {
    border-top: none;
    padding-top: 0;
  }
  figure, pre {
    page-break-inside: avoid;
  }
  figure {
    overflow: scroll;
  }
  pre.breakable {
    break-inside: auto;
  }
  h1, h2, h3, h4, h5, h6 {
    page-break-after: avoid;
  }
  h2+*, h3+*, h4+*, h5+*, h6+* {
    page-break-before: avoid;
  }
  pre {
    white-space: pre-wrap;
    word-wrap: break-word;
    font-size: 10pt;
  }
  table {
    border: 1px solid #ddd;
  }
  td {
    border-top: 1px solid #ddd;
  }
}

/* This is commented out here, as the string-set: doesn't
   pass W3C validation currently */
/*
.ears thead .left {
  string-set: ears-top-left content();
}

.ears thead .center {
  string-set: ears-top-center content();
}

.ears thead .right {
  string-set: ears-top-right content();
}

.ears tfoot .left {
  string-set: ears-bottom-left content();
}

.ears tfoot .center {
  string-set: ears-bottom-center content();
}

.ears tfoot .right {
  string-set: ears-bottom-right content();
}
*/

@page :first {
  padding-top: 0;
  @top-left {
    content: normal;
    border: none;
  }
  @top-center {
    content: normal;
    border: none;
  }
  @top-right {
    content: normal;
    border: none;
  }
}

@page {
  size: A4;
  margin-bottom: 45mm;
  padding-top: 20px;
  /* The following is commented out here, but set appropriately by in code, as
     the content depends on the document */
  /*
  @top-left {
    content: 'Internet-Draft';
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-left {
    content: string(ears-top-left);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-center {
    content: string(ears-top-center);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-right {
    content: string(ears-top-right);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @bottom-left {
    content: string(ears-bottom-left);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-center {
    content: string(ears-bottom-center);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-right {
      content: '[Page ' counter(page) ']';
      vertical-align: top;
      border-top: solid 1px #ccc;
  }
  */

}

/* Changes introduced to fix issues found during implementation */
/* Make sure links are clickable even if overlapped by following H* */
a {
  z-index: 2;
}
/* Separate body from document info even without intervening H1 */
section {
  clear: both;
}


/* Top align author divs, to avoid names without organization dropping level with org names */
.author {
  vertical-align: top;
}

/* Leave room in document info to show Internet-Draft on one line */
#identifiers dt {
  width: 8em;
}

/* Don't waste quite as much whitespace between label and value in doc info */
#identifiers dd {
  margin-left: 1em;
}

/* Give floating toc a background color (needed when it's a div inside section */
#toc {
  background-color: white;
}

/* Make the collapsed ToC header render white on gray also when it's a link */
@media screen and (max-width: 1023px) {
  #toc h2 a,
  #toc h2 a:link,
  #toc h2 a:focus,
  #toc h2 a:hover,
  #toc a.toplink,
  #toc a.toplink:hover {
    color: white;
    background-color: #444;
    text-decoration: none;
  }
}

/* Give the bottom of the ToC some whitespace */
@media screen and (min-width: 1024px) {
  #toc {
    padding: 0 0 1em 1em;
  }
}

/* Style section numbers with more space between number and title */
.section-number {
  padding-right: 0.5em;
}

/* prevent monospace from becoming overly large */
tt, code, pre {
  font-size: 95%;
}

/* Fix the height/width aspect for ascii art*/
pre.sourcecode,
.art-text pre {
  line-height: 1.12;
}


/* Add styling for a link in the ToC that points to the top of the document */
a.toplink {
  float: right;
  margin-right: 0.5em;
}

/* Fix the dl styling to match the RFC 7992 attributes */
dl > dt,
dl.dlParallel > dt {
  float: left;
  margin-right: 1em;
}
dl.dlNewline > dt {
  float: none;
}

/* Provide styling for table cell text alignment */
table td.text-left,
table th.text-left {
  text-align: left;
}
table td.text-center,
table th.text-center {
  text-align: center;
}
table td.text-right,
table th.text-right {
  text-align: right;
}

/* Make the alternative author contact information look less like just another
   author, and group it closer with the primary author contact information */
.alternative-contact {
  margin: 0.5em 0 0.25em 0;
}
address .non-ascii {
  margin: 0 0 0 2em;
}

/* With it being possible to set tables with alignment
  left, center, and right, { width: 100%; } does not make sense */
table {
  width: auto;
}

/* Avoid reference text that sits in a block with very wide left margin,
   because of a long floating dt label.*/
.references dd {
  overflow: visible;
}

/* Control caption placement */
caption {
  caption-side: bottom;
}

/* Limit the width of the author address vcard, so names in right-to-left
   script don't end up on the other side of the page. */

address.vcard {
  max-width: 30em;
  margin-right: auto;
}

/* For address alignment dependent on LTR or RTL scripts */
address div.left {
  text-align: left;
}
address div.right {
  text-align: right;
}

/* Provide table alignment support.  We can't use the alignX classes above
   since they do unwanted things with caption and other styling. */
table.right {
 margin-left: auto;
 margin-right: 0;
}
table.center {
 margin-left: auto;
 margin-right: auto;
}
table.left {
 margin-left: 0;
 margin-right: auto;
}

/* Give the table caption label the same styling as the figcaption */
caption a[href] {
  color: #222;
}

@media print {
  .toplink {
    display: none;
  }

  /* avoid overwriting the top border line with the ToC header */
  #toc {
    padding-top: 1px;
  }

  /* Avoid page breaks inside dl and author address entries */
  .vcard {
    page-break-inside: avoid;
  }

}
/* Tweak the bcp14 keyword presentation */
.bcp14 {
  font-variant: small-caps;
  font-weight: bold;
  font-size: 0.9em;
}
/* Tweak the invisible space above H* in order not to overlay links in text above */
 h2 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 31px;
 }
 h3 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
 h4 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
/* Float artwork pilcrow to the right */
@media screen {
  .artwork a.pilcrow {
    display: block;
    line-height: 0.7;
    margin-top: 0.15em;
  }
}
/* Make pilcrows on dd visible */
@media screen {
  dd:hover > a.pilcrow {
    visibility: visible;
  }
}
/* Make the placement of figcaption match that of a table's caption
   by removing the figure's added bottom margin */
.alignLeft.art-text,
.alignCenter.art-text,
.alignRight.art-text {
   margin-bottom: 0;
}
.alignLeft,
.alignCenter,
.alignRight {
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<table class="ears">
<thead><tr>
<td class="left">RFC 9325</td>
<td class="center">TLS/DTLS Recommendations</td>
<td class="right">November 2022</td>
</tr></thead>
<tfoot><tr>
<td class="left">Sheffer, et al.</td>
<td class="center">Best Current Practice</td>
<td class="right">[Page]</td>
</tr></tfoot>
</table>
<div id="external-metadata" class="document-information"></div>
<div id="internal-metadata" class="document-information">
<dl id="identifiers">
<dt class="label-stream">Stream:</dt>
<dd class="stream">Internet Engineering Task Force (IETF)</dd>
<dt class="label-rfc">RFC:</dt>
<dd class="rfc"><a href="https://www.rfc-editor.org/rfc/rfc9325" class="eref">9325</a></dd>
<dt class="label-bcp">BCP:</dt>
<dd class="bcp">195</dd>
<dt class="label-obsoletes">Obsoletes:</dt>
<dd class="obsoletes">
<a href="https://www.rfc-editor.org/rfc/rfc7525" class="eref">7525</a> </dd>
<dt class="label-updates">Updates:</dt>
<dd class="updates">
<a href="https://www.rfc-editor.org/rfc/rfc5288" class="eref">5288</a>, <a href="https://www.rfc-editor.org/rfc/rfc6066" class="eref">6066</a> </dd>
<dt class="label-category">Category:</dt>
<dd class="category">Best Current Practice</dd>
<dt class="label-published">Published:</dt>
<dd class="published">
<time datetime="2022-11" class="published">November 2022</time>
    </dd>
<dt class="label-issn">ISSN:</dt>
<dd class="issn">2070-1721</dd>
<dt class="label-authors">Authors:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">Y. Sheffer</div>
<div class="org">Intuit</div>
</div>
<div class="author">
      <div class="author-name">P. Saint-Andre</div>
<div class="org">Independent</div>
</div>
<div class="author">
      <div class="author-name">T. Fossati</div>
<div class="org">ARM Limited</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 9325</h1>
<h1 id="title">Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are used to protect data exchanged over a wide range of application protocols and can also form the basis for secure transport protocols.  Over the years, the industry has witnessed several serious attacks on TLS and DTLS, including attacks on the most commonly used cipher suites and their modes of operation.  This document provides the latest recommendations for ensuring the security of deployed services that use TLS and DTLS. These recommendations are applicable to the majority of use cases.<a href="#section-abstract-1" class="pilcrow">¶</a></p>
<p id="section-abstract-2">RFC 7525, an earlier version of the TLS recommendations, was published when the industry was transitioning to TLS 1.2. Years later, this transition is largely complete, and TLS 1.3 is widely available. This document updates the guidance given the new environment and obsoletes RFC 7525. In addition, this document updates RFCs 5288 and 6066 in view of recent attacks.<a href="#section-abstract-2" class="pilcrow">¶</a></p>
</section>
<div id="status-of-memo">
<section id="section-boilerplate.1">
        <h2 id="name-status-of-this-memo">
<a href="#name-status-of-this-memo" class="section-name selfRef">Status of This Memo</a>
        </h2>
<p id="section-boilerplate.1-1">
            This memo documents an Internet Best Current Practice.<a href="#section-boilerplate.1-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-2">
            This document is a product of the Internet Engineering Task Force
            (IETF).  It represents the consensus of the IETF community.  It has
            received public review and has been approved for publication by
            the Internet Engineering Steering Group (IESG).  Further information
            on BCPs is available in Section 2 of RFC 7841.<a href="#section-boilerplate.1-2" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <span><a href="https://www.rfc-editor.org/info/rfc9325">https://www.rfc-editor.org/info/rfc9325</a></span>.<a href="#section-boilerplate.1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="copyright">
<section id="section-boilerplate.2">
        <h2 id="name-copyright-notice">
<a href="#name-copyright-notice" class="section-name selfRef">Copyright Notice</a>
        </h2>
<p id="section-boilerplate.2-1">
            Copyright (c) 2022 IETF Trust and the persons identified as the
            document authors. All rights reserved.<a href="#section-boilerplate.2-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<span><a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a></span>) in effect on the date of
            publication of this document. Please review these documents
            carefully, as they describe your rights and restrictions with
            respect to this document. Code Components extracted from this
            document must include Revised BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Revised BSD License.<a href="#section-boilerplate.2-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="toc">
<section id="section-toc.1">
        <a href="#" onclick="scroll(0,0)" class="toplink">▲</a><h2 id="name-table-of-contents">
<a href="#name-table-of-contents" class="section-name selfRef">Table of Contents</a>
        </h2>
<nav class="toc"><ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.1">
            <p id="section-toc.1-1.1.1" class="keepWithNext"><a href="#section-1" class="auto internal xref">1</a>.  <a href="#name-introduction" class="internal xref">Introduction</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.2">
            <p id="section-toc.1-1.2.1" class="keepWithNext"><a href="#section-2" class="auto internal xref">2</a>.  <a href="#name-terminology" class="internal xref">Terminology</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1"><a href="#section-3" class="auto internal xref">3</a>.  <a href="#name-general-recommendations" class="internal xref">General Recommendations</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.1">
                <p id="section-toc.1-1.3.2.1.1"><a href="#section-3.1" class="auto internal xref">3.1</a>.  <a href="#name-protocol-versions" class="internal xref">Protocol Versions</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.1.2.1">
                    <p id="section-toc.1-1.3.2.1.2.1.1" class="keepWithNext"><a href="#section-3.1.1" class="auto internal xref">3.1.1</a>.  <a href="#name-ssl-tls-protocol-versions" class="internal xref">SSL/TLS Protocol Versions</a></p>
</li>
                  <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.1.2.2">
                    <p id="section-toc.1-1.3.2.1.2.2.1"><a href="#section-3.1.2" class="auto internal xref">3.1.2</a>.  <a href="#name-dtls-protocol-versions" class="internal xref">DTLS Protocol Versions</a></p>
</li>
                  <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.1.2.3">
                    <p id="section-toc.1-1.3.2.1.2.3.1"><a href="#section-3.1.3" class="auto internal xref">3.1.3</a>.  <a href="#name-fallback-to-lower-versions" class="internal xref">Fallback to Lower Versions</a></p>
</li>
                </ul>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.2">
                <p id="section-toc.1-1.3.2.2.1"><a href="#section-3.2" class="auto internal xref">3.2</a>.  <a href="#name-strict-tls" class="internal xref">Strict TLS</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.3">
                <p id="section-toc.1-1.3.2.3.1"><a href="#section-3.3" class="auto internal xref">3.3</a>.  <a href="#name-compression" class="internal xref">Compression</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.3.2.1">
                    <p id="section-toc.1-1.3.2.3.2.1.1"><a href="#section-3.3.1" class="auto internal xref">3.3.1</a>.  <a href="#name-certificate-compression" class="internal xref">Certificate Compression</a></p>
</li>
                </ul>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.4">
                <p id="section-toc.1-1.3.2.4.1"><a href="#section-3.4" class="auto internal xref">3.4</a>.  <a href="#name-tls-session-resumption" class="internal xref">TLS Session Resumption</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.5">
                <p id="section-toc.1-1.3.2.5.1"><a href="#section-3.5" class="auto internal xref">3.5</a>.  <a href="#name-renegotiation-in-tls-12" class="internal xref">Renegotiation in TLS 1.2</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.6">
                <p id="section-toc.1-1.3.2.6.1"><a href="#section-3.6" class="auto internal xref">3.6</a>.  <a href="#name-post-handshake-authenticati" class="internal xref">Post-Handshake Authentication</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.7">
                <p id="section-toc.1-1.3.2.7.1"><a href="#section-3.7" class="auto internal xref">3.7</a>.  <a href="#name-server-name-indication-sni" class="internal xref">Server Name Indication (SNI)</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.8">
                <p id="section-toc.1-1.3.2.8.1"><a href="#section-3.8" class="auto internal xref">3.8</a>.  <a href="#name-application-layer-protocol-" class="internal xref">Application-Layer Protocol Negotiation (ALPN)</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.9">
                <p id="section-toc.1-1.3.2.9.1"><a href="#section-3.9" class="auto internal xref">3.9</a>.  <a href="#name-multi-server-deployment" class="internal xref">Multi-Server Deployment</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3.2.10">
                <p id="section-toc.1-1.3.2.10.1"><a href="#section-3.10" class="auto internal xref">3.10</a>. <a href="#name-zero-round-trip-time-0-rtt-" class="internal xref">Zero Round-Trip Time (0-RTT) Data in TLS 1.3</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.4">
            <p id="section-toc.1-1.4.1"><a href="#section-4" class="auto internal xref">4</a>.  <a href="#name-recommendations-cipher-suit" class="internal xref">Recommendations: Cipher Suites</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.4.2.1">
                <p id="section-toc.1-1.4.2.1.1"><a href="#section-4.1" class="auto internal xref">4.1</a>.  <a href="#name-general-guidelines" class="internal xref">General Guidelines</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.4.2.2">
                <p id="section-toc.1-1.4.2.2.1"><a href="#section-4.2" class="auto internal xref">4.2</a>.  <a href="#name-cipher-suites-for-tls-12" class="internal xref">Cipher Suites for TLS 1.2</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.4.2.2.2.1">
                    <p id="section-toc.1-1.4.2.2.2.1.1"><a href="#section-4.2.1" class="auto internal xref">4.2.1</a>.  <a href="#name-implementation-details" class="internal xref">Implementation Details</a></p>
</li>
                </ul>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.4.2.3">
                <p id="section-toc.1-1.4.2.3.1"><a href="#section-4.3" class="auto internal xref">4.3</a>.  <a href="#name-cipher-suites-for-tls-13" class="internal xref">Cipher Suites for TLS 1.3</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.4.2.4">
                <p id="section-toc.1-1.4.2.4.1"><a href="#section-4.4" class="auto internal xref">4.4</a>.  <a href="#name-limits-on-key-usage" class="internal xref">Limits on Key Usage</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.4.2.5">
                <p id="section-toc.1-1.4.2.5.1"><a href="#section-4.5" class="auto internal xref">4.5</a>.  <a href="#name-public-key-length" class="internal xref">Public Key Length</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.4.2.6">
                <p id="section-toc.1-1.4.2.6.1"><a href="#section-4.6" class="auto internal xref">4.6</a>.  <a href="#name-truncated-hmac" class="internal xref">Truncated HMAC</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.5">
            <p id="section-toc.1-1.5.1"><a href="#section-5" class="auto internal xref">5</a>.  <a href="#name-applicability-statement" class="internal xref">Applicability Statement</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.5.2.1">
                <p id="section-toc.1-1.5.2.1.1"><a href="#section-5.1" class="auto internal xref">5.1</a>.  <a href="#name-security-services" class="internal xref">Security Services</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.5.2.2">
                <p id="section-toc.1-1.5.2.2.1"><a href="#section-5.2" class="auto internal xref">5.2</a>.  <a href="#name-opportunistic-security" class="internal xref">Opportunistic Security</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.6">
            <p id="section-toc.1-1.6.1"><a href="#section-6" class="auto internal xref">6</a>.  <a href="#name-iana-considerations" class="internal xref">IANA Considerations</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-7" class="auto internal xref">7</a>.  <a href="#name-security-considerations" class="internal xref">Security Considerations</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.7.2.1">
                <p id="section-toc.1-1.7.2.1.1"><a href="#section-7.1" class="auto internal xref">7.1</a>.  <a href="#name-host-name-validation" class="internal xref">Host Name Validation</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.7.2.2">
                <p id="section-toc.1-1.7.2.2.1"><a href="#section-7.2" class="auto internal xref">7.2</a>.  <a href="#name-aes-gcm" class="internal xref">AES-GCM</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.7.2.2.2.1">
                    <p id="section-toc.1-1.7.2.2.2.1.1"><a href="#section-7.2.1" class="auto internal xref">7.2.1</a>.  <a href="#name-nonce-reuse-in-tls-12" class="internal xref">Nonce Reuse in TLS 1.2</a></p>
</li>
                </ul>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.7.2.3">
                <p id="section-toc.1-1.7.2.3.1"><a href="#section-7.3" class="auto internal xref">7.3</a>.  <a href="#name-forward-secrecy" class="internal xref">Forward Secrecy</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.7.2.4">
                <p id="section-toc.1-1.7.2.4.1"><a href="#section-7.4" class="auto internal xref">7.4</a>.  <a href="#name-diffie-hellman-exponent-reu" class="internal xref">Diffie-Hellman Exponent Reuse</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.7.2.5">
                <p id="section-toc.1-1.7.2.5.1"><a href="#section-7.5" class="auto internal xref">7.5</a>.  <a href="#name-certificate-revocation" class="internal xref">Certificate Revocation</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-8" class="auto internal xref">8</a>.  <a href="#name-references" class="internal xref">References</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.8.2.1">
                <p id="section-toc.1-1.8.2.1.1"><a href="#section-8.1" class="auto internal xref">8.1</a>.  <a href="#name-normative-references" class="internal xref">Normative References</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.8.2.2">
                <p id="section-toc.1-1.8.2.2.1"><a href="#section-8.2" class="auto internal xref">8.2</a>.  <a href="#name-informative-references" class="internal xref">Informative References</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.9">
            <p id="section-toc.1-1.9.1"><a href="#appendix-A" class="auto internal xref">Appendix A</a>.  <a href="#name-differences-from-rfc-7525" class="internal xref">Differences from RFC 7525</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.10">
            <p id="section-toc.1-1.10.1"><a href="#appendix-B" class="auto internal xref"></a><a href="#name-acknowledgments" class="internal xref">Acknowledgments</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.11">
            <p id="section-toc.1-1.11.1"><a href="#appendix-C" class="auto internal xref"></a><a href="#name-authors-addresses" class="internal xref">Authors' Addresses</a></p>
</li>
        </ul>
</nav>
</section>
</div>
<div id="introduction">
<section id="section-1">
      <h2 id="name-introduction">
<a href="#section-1" class="section-number selfRef">1. </a><a href="#name-introduction" class="section-name selfRef">Introduction</a>
      </h2>
<p id="section-1-1">Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are used to protect data exchanged over a wide variety of application protocols, including HTTP <span>[<a href="#RFC9112" class="cite xref">RFC9112</a>]</span> <span>[<a href="#RFC9113" class="cite xref">RFC9113</a>]</span>, IMAP <span>[<a href="#RFC9051" class="cite xref">RFC9051</a>]</span>, Post Office Protocol (POP) <span>[<a href="#STD53" class="cite xref">STD53</a>]</span>, SIP <span>[<a href="#RFC3261" class="cite xref">RFC3261</a>]</span>, SMTP <span>[<a href="#RFC5321" class="cite xref">RFC5321</a>]</span>, and the Extensible Messaging and Presence Protocol (XMPP) <span>[<a href="#RFC6120" class="cite xref">RFC6120</a>]</span>.  Such protocols use both the TLS or DTLS handshake protocol and the TLS or DTLS record layer.



      Although the TLS handshake protocol can also be used with different record layers to define secure transport protocols (the most prominent example is QUIC <span>[<a href="#RFC9000" class="cite xref">RFC9000</a>]</span>), such transport protocols are not directly in scope for this document; nevertheless, many of the recommendations here might apply insofar as such protocols use the TLS handshake protocol.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">Over the years leading to 2015, the industry had witnessed serious attacks on TLS and DTLS, including attacks on the most commonly used cipher suites and their modes of operation.  For instance, both the AES-CBC <span>[<a href="#RFC3602" class="cite xref">RFC3602</a>]</span> and RC4 <span>[<a href="#RFC7465" class="cite xref">RFC7465</a>]</span> encryption algorithms, which together were once the most widely deployed ciphers, were attacked in the context of TLS.  Detailed information about the attacks known prior to 2015 is provided in a companion document <span>[<a href="#RFC7457" class="cite xref">RFC7457</a>]</span> to the previous version of the TLS recommendations <span>[<a href="#RFC7525" class="cite xref">RFC7525</a>]</span>, which will help the reader understand the rationale behind the recommendations provided here. That document has not been updated in concert with this one; instead, newer attacks are described in this document, as are mitigations for those attacks.<a href="#section-1-2" class="pilcrow">¶</a></p>
<p id="section-1-3">The TLS community reacted to the attacks described in <span>[<a href="#RFC7457" class="cite xref">RFC7457</a>]</span> in several ways:<a href="#section-1-3" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-1-4.1">Detailed guidance was published on the use of TLS 1.2 <span>[<a href="#RFC5246" class="cite xref">RFC5246</a>]</span> and DTLS 1.2 <span>[<a href="#RFC6347" class="cite xref">RFC6347</a>]</span> along with earlier protocol versions. This guidance is included in the original <span>[<a href="#RFC7525" class="cite xref">RFC7525</a>]</span> and mostly retained in this revised version; note that this guidance was mostly adopted by the industry since the publication of RFC 7525 in 2015.<a href="#section-1-4.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-1-4.2">Versions of TLS earlier than 1.2 were deprecated <span>[<a href="#RFC8996" class="cite xref">RFC8996</a>]</span>.<a href="#section-1-4.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-1-4.3">Version 1.3 of TLS <span>[<a href="#RFC8446" class="cite xref">RFC8446</a>]</span> was released, followed by version 1.3 of DTLS <span>[<a href="#RFC9147" class="cite xref">RFC9147</a>]</span>; these versions largely mitigate or resolve the described attacks.<a href="#section-1-4.3" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-1-5">Those who implement and deploy TLS and TLS-based protocols need guidance on how they can be used securely.  This document provides guidance for deployed services as well as for software implementations, assuming the implementer expects their code to be deployed in the environments defined in <a href="#applicability" class="auto internal xref">Section 5</a>. Concerning deployment, this document targets a wide audience, namely all deployers who wish to add authentication (be it one-way only or mutual), confidentiality, and data integrity protection to their communications.<a href="#section-1-5" class="pilcrow">¶</a></p>
<p id="section-1-6">The recommendations herein take into consideration the security of various mechanisms, their technical maturity and interoperability, and their prevalence in implementations at the time of writing.  Unless it is explicitly called out that a recommendation applies to TLS alone or to DTLS alone, each recommendation applies to both TLS and DTLS.<a href="#section-1-6" class="pilcrow">¶</a></p>
<p id="section-1-7">This document attempts to minimize new guidance to TLS 1.2 implementations, and the overall approach is to encourage systems to move to TLS 1.3. However, this is not always practical. Newly discovered attacks, as well as ecosystem changes, necessitated some new requirements that apply to TLS 1.2 environments. Those are summarized in <a href="#diff-rfc" class="auto internal xref">Appendix A</a>.<a href="#section-1-7" class="pilcrow">¶</a></p>
<p id="section-1-8">Naturally, future attacks are likely, and this document cannot address them.  Those who implement and deploy TLS/DTLS and protocols based on TLS/DTLS are strongly advised to pay attention to future developments.  In particular, although it is known that the creation of quantum computers will have a significant impact on the security of cryptographic primitives and the technologies that use them, currently post-quantum cryptography is a work in progress and it is too early to make recommendations; once the relevant specifications are standardized in the IETF or elsewhere, this document should be updated to reflect best practices at that time.<a href="#section-1-8" class="pilcrow">¶</a></p>
<p id="section-1-9">As noted, the TLS 1.3 specification resolves many of the vulnerabilities listed in this document. A system that deploys TLS 1.3 should have fewer vulnerabilities than TLS 1.2 or below. Therefore, this document replaces <span>[<a href="#RFC7525" class="cite xref">RFC7525</a>]</span>, with an explicit goal to encourage migration of most uses of TLS 1.2 to TLS 1.3.<a href="#section-1-9" class="pilcrow">¶</a></p>
<p id="section-1-10">These are minimum recommendations for the use of TLS in the vast majority of implementation and deployment scenarios, with the exception of unauthenticated TLS (see <a href="#applicability" class="auto internal xref">Section 5</a>). Other specifications that reference this document can have stricter requirements related to one or more aspects of the protocol, based on their particular circumstances (e.g., for use with a specific application protocol); when that is the case, implementers are advised to adhere to those stricter requirements. Furthermore, this document provides a floor, not a ceiling: where feasible, administrators of services are encouraged to go beyond the minimum support available in implementations to provide the strongest security possible. For example, based on knowledge about the deployed base for an existing application protocol and a cost-benefit analysis regarding security strength vs. interoperability, a given service provider might decide to disable TLS 1.2 entirely and offer only TLS 1.3.<a href="#section-1-10" class="pilcrow">¶</a></p>
<p id="section-1-11">Community knowledge about the strength of various algorithms and feasible attacks can change quickly, and experience shows that a Best Current Practice (BCP) document about security is a point-in-time statement.  Readers are advised to seek out any errata or updates that apply to this document.<a href="#section-1-11" class="pilcrow">¶</a></p>
<p id="section-1-12">This document updates <span>[<a href="#RFC5288" class="cite xref">RFC5288</a>]</span> in view of the <span>[<a href="#Boeck2016" class="cite xref">Boeck2016</a>]</span> attack. See <a href="#nonce-reuse" class="auto internal xref">Section 7.2.1</a> for the details.<a href="#section-1-12" class="pilcrow">¶</a></p>
<p id="section-1-13">This document updates <span>[<a href="#RFC6066" class="cite xref">RFC6066</a>]</span> in view of the <span>[<a href="#ALPACA" class="cite xref">ALPACA</a>]</span> attack.  See <a href="#sni" class="auto internal xref">Section 3.7</a> for the details.<a href="#section-1-13" class="pilcrow">¶</a></p>
</section>
</div>
<div id="terminology">
<section id="section-2">
      <h2 id="name-terminology">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-terminology" class="section-name selfRef">Terminology</a>
      </h2>
<p id="section-2-1">A number of security-related terms in this document are used in the sense defined in <span>[<a href="#RFC4949" class="cite xref">RFC4949</a>]</span>,
including "attack", "authentication", "certificate", "cipher", "compromise", "confidentiality", 
"credential", "data integrity", "encryption", "forward secrecy", "key", "key length", "self-signed certificate", 
"strength", and "strong".<a href="#section-2-1" class="pilcrow">¶</a></p>
<p id="section-2-2">The key words "<span class="bcp14">MUST</span>", "<span class="bcp14">MUST NOT</span>",
"<span class="bcp14">REQUIRED</span>", "<span class="bcp14">SHALL</span>", "<span class="bcp14">SHALL NOT</span>",
"<span class="bcp14">SHOULD</span>", "<span class="bcp14">SHOULD NOT</span>",
"<span class="bcp14">RECOMMENDED</span>", "<span class="bcp14">NOT RECOMMENDED</span>",
"<span class="bcp14">MAY</span>", and "<span class="bcp14">OPTIONAL</span>" in this document are to be
interpreted as described in BCP 14 <span>[<a href="#RFC2119" class="cite xref">RFC2119</a>]</span> <span>[<a href="#RFC8174" class="cite xref">RFC8174</a>]</span> when, and only when, they appear in all capitals, as shown
here.<a href="#section-2-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="rec">
<section id="section-3">
      <h2 id="name-general-recommendations">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-general-recommendations" class="section-name selfRef">General Recommendations</a>
      </h2>
<p id="section-3-1">This section provides general recommendations on the secure use of TLS. Recommendations related to cipher suites are discussed in the following section.<a href="#section-3-1" class="pilcrow">¶</a></p>
<div id="protocol-versions">
<section id="section-3.1">
        <h3 id="name-protocol-versions">
<a href="#section-3.1" class="section-number selfRef">3.1. </a><a href="#name-protocol-versions" class="section-name selfRef">Protocol Versions</a>
        </h3>
<div id="rec-versions">
<section id="section-3.1.1">
          <h4 id="name-ssl-tls-protocol-versions">
<a href="#section-3.1.1" class="section-number selfRef">3.1.1. </a><a href="#name-ssl-tls-protocol-versions" class="section-name selfRef">SSL/TLS Protocol Versions</a>
          </h4>
<p id="section-3.1.1-1">It is important both to stop using old, less secure versions of SSL/TLS and to start using modern, more secure versions; therefore, the following are the recommendations concerning TLS/SSL protocol versions:<a href="#section-3.1.1-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-3.1.1-2.1">
              <p id="section-3.1.1-2.1.1">Implementations <span class="bcp14">MUST NOT</span> negotiate SSL version 2.<a href="#section-3.1.1-2.1.1" class="pilcrow">¶</a></p>
<p id="section-3.1.1-2.1.2">
Rationale: Today, SSLv2 is considered insecure <span>[<a href="#RFC6176" class="cite xref">RFC6176</a>]</span>.<a href="#section-3.1.1-2.1.2" class="pilcrow">¶</a></p>
</li>
            <li class="normal" id="section-3.1.1-2.2">
              <p id="section-3.1.1-2.2.1">Implementations <span class="bcp14">MUST NOT</span> negotiate SSL version 3.<a href="#section-3.1.1-2.2.1" class="pilcrow">¶</a></p>
<p id="section-3.1.1-2.2.2">
Rationale: SSLv3 <span>[<a href="#RFC6101" class="cite xref">RFC6101</a>]</span> was an improvement over SSLv2 and plugged some significant security holes but did not support strong cipher suites. SSLv3 does not support TLS extensions, some of which (e.g., renegotiation_info <span>[<a href="#RFC5746" class="cite xref">RFC5746</a>]</span>) are security critical.  In addition, with the emergence of the Padding Oracle On Downgraded Legacy Encryption (POODLE) attack <span>[<a href="#POODLE" class="cite xref">POODLE</a>]</span>, SSLv3 is now widely recognized as fundamentally insecure.  See <span>[<a href="#RFC7568" class="cite xref">RFC7568</a>]</span> for further details.<a href="#section-3.1.1-2.2.2" class="pilcrow">¶</a></p>
</li>
            <li class="normal" id="section-3.1.1-2.3">
              <p id="section-3.1.1-2.3.1">Implementations <span class="bcp14">MUST NOT</span> negotiate TLS version 1.0 <span>[<a href="#RFC2246" class="cite xref">RFC2246</a>]</span>.<a href="#section-3.1.1-2.3.1" class="pilcrow">¶</a></p>
<p id="section-3.1.1-2.3.2">
Rationale: TLS 1.0 (published in 1999) does not support many modern, strong cipher suites. In addition, TLS 1.0 lacks a per-record Initialization Vector (IV) for cipher suites based on cipher block chaining (CBC) and does not warn against common padding errors. This and other recommendations in this section are in line with <span>[<a href="#RFC8996" class="cite xref">RFC8996</a>]</span>.<a href="#section-3.1.1-2.3.2" class="pilcrow">¶</a></p>
</li>
            <li class="normal" id="section-3.1.1-2.4">
              <p id="section-3.1.1-2.4.1">Implementations <span class="bcp14">MUST NOT</span> negotiate TLS version 1.1 <span>[<a href="#RFC4346" class="cite xref">RFC4346</a>]</span>.<a href="#section-3.1.1-2.4.1" class="pilcrow">¶</a></p>
<p id="section-3.1.1-2.4.2">
Rationale: TLS 1.1 (published in 2006) is a security improvement over TLS 1.0 but still does not support certain stronger cipher suites that were introduced with the standardization of TLS 1.2 in 2008, including the cipher suites recommended for TLS 1.2 by this document (see <a href="#rec-cipher" class="auto internal xref">Section 4.2</a> below).<a href="#section-3.1.1-2.4.2" class="pilcrow">¶</a></p>
</li>
            <li class="normal" id="section-3.1.1-2.5">
              <p id="section-3.1.1-2.5.1">Implementations <span class="bcp14">MUST</span> support TLS 1.2 <span>[<a href="#RFC5246" class="cite xref">RFC5246</a>]</span>.<a href="#section-3.1.1-2.5.1" class="pilcrow">¶</a></p>
<p id="section-3.1.1-2.5.2">
Rationale: TLS 1.2 is implemented and deployed more widely than TLS 1.3 at this time, and when the recommendations in this document are followed to mitigate known attacks, the use of TLS 1.2 is as safe as the use of TLS 1.3.  In most application protocols that reuse TLS and DTLS, there is no immediate need to migrate solely to TLS 1.3. Indeed, because many application clients are dependent on TLS libraries or operating systems that do not yet support TLS 1.3, proactively deprecating TLS 1.2 would introduce significant interoperability issues, thus harming security more than helping it.  Nevertheless, it is expected that a future version of this BCP will deprecate the use of TLS 1.2 when it is appropriate to do so.<a href="#section-3.1.1-2.5.2" class="pilcrow">¶</a></p>
</li>
            <li class="normal" id="section-3.1.1-2.6">
              <p id="section-3.1.1-2.6.1">Implementations <span class="bcp14">SHOULD</span> support TLS 1.3 <span>[<a href="#RFC8446" class="cite xref">RFC8446</a>]</span> and, if implemented, <span class="bcp14">MUST</span> prefer to negotiate TLS 1.3 over earlier versions of TLS.<a href="#section-3.1.1-2.6.1" class="pilcrow">¶</a></p>
<p id="section-3.1.1-2.6.2">
Rationale: TLS 1.3 is a major overhaul to the protocol and resolves many of the security issues with TLS 1.2. To the extent that an implementation supports TLS 1.2 (even if it defaults to TLS 1.3), it <span class="bcp14">MUST</span> follow the recommendations regarding TLS 1.2 specified in this document.<a href="#section-3.1.1-2.6.2" class="pilcrow">¶</a></p>
</li>
            <li class="normal" id="section-3.1.1-2.7">
              <p id="section-3.1.1-2.7.1">New transport protocols that integrate the TLS/DTLS handshake protocol and/or record layer <span class="bcp14">MUST</span> use only TLS/DTLS 1.3 (for instance, QUIC <span>[<a href="#RFC9001" class="cite xref">RFC9001</a>]</span> took this approach). New application protocols that employ TLS/DTLS for channel or session encryption <span class="bcp14">MUST</span> integrate with both TLS/DTLS versions 1.2 and 1.3; nevertheless, in rare cases where broad interoperability is not a concern, application protocol designers <span class="bcp14">MAY</span> choose to forego TLS 1.2.<a href="#section-3.1.1-2.7.1" class="pilcrow">¶</a></p>
<p id="section-3.1.1-2.7.2">
Rationale: Secure deployment of TLS 1.3 is significantly easier and less error prone than secure deployment of TLS 1.2. When designing a new secure transport protocol such as QUIC, there is no reason to support TLS 1.2. By contrast, new application protocols that reuse TLS need to support both TLS 1.3 and TLS 1.2 in order to take advantage of underlying library or operating system support for both versions.<a href="#section-3.1.1-2.7.2" class="pilcrow">¶</a></p>
</li>
          </ul>
<p id="section-3.1.1-3">This BCP applies to TLS 1.3, TLS 1.2, and earlier versions. It is not safe for readers to assume that the recommendations in this BCP apply to any future version of TLS.<a href="#section-3.1.1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="dtls-protocol-versions">
<section id="section-3.1.2">
          <h4 id="name-dtls-protocol-versions">
<a href="#section-3.1.2" class="section-number selfRef">3.1.2. </a><a href="#name-dtls-protocol-versions" class="section-name selfRef">DTLS Protocol Versions</a>
          </h4>
<p id="section-3.1.2-1">DTLS, an adaptation of TLS for UDP datagrams, was introduced when TLS 1.1 was published.  The following are the recommendations with respect to DTLS:<a href="#section-3.1.2-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-3.1.2-2.1">
              <p id="section-3.1.2-2.1.1">Implementations <span class="bcp14">MUST NOT</span> negotiate DTLS version 1.0 <span>[<a href="#RFC4347" class="cite xref">RFC4347</a>]</span>.<a href="#section-3.1.2-2.1.1" class="pilcrow">¶</a></p>
<p id="section-3.1.2-2.1.2">
Version 1.0 of DTLS correlates to version 1.1 of TLS (see above).<a href="#section-3.1.2-2.1.2" class="pilcrow">¶</a></p>
</li>
            <li class="normal" id="section-3.1.2-2.2">
              <p id="section-3.1.2-2.2.1">Implementations <span class="bcp14">MUST</span> support DTLS 1.2 <span>[<a href="#RFC6347" class="cite xref">RFC6347</a>]</span>.<a href="#section-3.1.2-2.2.1" class="pilcrow">¶</a></p>
<p id="section-3.1.2-2.2.2">
Version 1.2 of DTLS correlates to version 1.2 of TLS (see above).
(There is no version 1.1 of DTLS.)<a href="#section-3.1.2-2.2.2" class="pilcrow">¶</a></p>
</li>
            <li class="normal" id="section-3.1.2-2.3">
              <p id="section-3.1.2-2.3.1">Implementations <span class="bcp14">SHOULD</span> support DTLS 1.3 <span>[<a href="#RFC9147" class="cite xref">RFC9147</a>]</span> and, if implemented, <span class="bcp14">MUST</span> prefer to negotiate DTLS version 1.3 over earlier versions of DTLS.<a href="#section-3.1.2-2.3.1" class="pilcrow">¶</a></p>
<p id="section-3.1.2-2.3.2">
Version 1.3 of DTLS correlates to version 1.3 of TLS (see above).<a href="#section-3.1.2-2.3.2" class="pilcrow">¶</a></p>
</li>
          </ul>
</section>
</div>
<div id="rec-fallback">
<section id="section-3.1.3">
          <h4 id="name-fallback-to-lower-versions">
<a href="#section-3.1.3" class="section-number selfRef">3.1.3. </a><a href="#name-fallback-to-lower-versions" class="section-name selfRef">Fallback to Lower Versions</a>
          </h4>
<p id="section-3.1.3-1">TLS/DTLS 1.2 clients <span class="bcp14">MUST NOT</span> fall back to earlier TLS versions, since those versions have been deprecated <span>[<a href="#RFC8996" class="cite xref">RFC8996</a>]</span>. As a result, the downgrade-protection Signaling Cipher Suite Value (SCSV) mechanism <span>[<a href="#RFC7507" class="cite xref">RFC7507</a>]</span> is no longer needed for clients. In addition, TLS 1.3 implements a new version-negotiation mechanism.<a href="#section-3.1.3-1" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="strict-tls">
<section id="section-3.2">
        <h3 id="name-strict-tls">
<a href="#section-3.2" class="section-number selfRef">3.2. </a><a href="#name-strict-tls" class="section-name selfRef">Strict TLS</a>
        </h3>
<p id="section-3.2-1">The following recommendations are provided to help prevent "SSL Stripping" and STARTTLS command injection (attacks that are summarized in <span>[<a href="#RFC7457" class="cite xref">RFC7457</a>]</span>):<a href="#section-3.2-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-3.2-2.1">Many existing application protocols were designed before the use of TLS became common. These protocols typically support TLS in one of two ways: either via a separate port for TLS-only communication (e.g., port 443 for HTTPS) or via a method for dynamically upgrading a channel from unencrypted to TLS protected (e.g., STARTTLS, which is used in protocols such as IMAP and XMPP). Regardless of the mechanism for protecting the communication channel (TLS-only port or dynamic upgrade), what matters is the end state of the channel. When a protocol defines both a dynamic upgrade method and a separate TLS-only method, then the separate TLS-only method <span class="bcp14">MUST</span> be supported by implementations and <span class="bcp14">MUST</span> be configured by administrators to be used in preference to the dynamic upgrade method.  When a protocol supports only a dynamic upgrade method, implementations <span class="bcp14">MUST</span> provide a way for administrators to set a strict local policy that forbids use of plaintext in the absence of a negotiated TLS channel, and administrators <span class="bcp14">MUST</span> use this policy.<a href="#section-3.2-2.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-3.2-2.2">HTTP client and server implementations intended for use in the World Wide Web (see 
<a href="#applicability" class="auto internal xref">Section 5</a>) <span class="bcp14">MUST</span> support the HTTP Strict Transport Security (HSTS) header 
field <span>[<a href="#RFC6797" class="cite xref">RFC6797</a>]</span> so that web servers can advertise that they are willing to 
accept TLS-only clients. Web servers <span class="bcp14">SHOULD</span> use HSTS to indicate that they are 
willing to accept TLS-only clients, unless they are deployed in such a way that 
using HSTS would in fact weaken overall security (e.g., it can be problematic to 
use HSTS with self-signed certificates, as described in <span><a href="https://www.rfc-editor.org/rfc/rfc6797#section-11.3" class="relref">Section 11.3</a> of [<a href="#RFC6797" class="cite xref">RFC6797</a>]</span>).
Similar technologies exist for non-HTTP application protocols, such as Mail Transfer Agent Strict Transport Security (MTA-STS) for 
mail transfer agents <span>[<a href="#RFC8461" class="cite xref">RFC8461</a>]</span> and methods based on DNS-Based Authentication of 
Named Entities (DANE) <span>[<a href="#RFC6698" class="cite xref">RFC6698</a>]</span> for SMTP <span>[<a href="#RFC7672" class="cite xref">RFC7672</a>]</span> and XMPP <span>[<a href="#RFC7712" class="cite xref">RFC7712</a>]</span>.<a href="#section-3.2-2.2" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-3.2-3">Rationale: Combining unprotected and TLS-protected communication opens the way to SSL Stripping and similar attacks, since an initial part of the communication is not integrity protected and therefore can be manipulated by an attacker whose goal is to keep the communication in the clear.<a href="#section-3.2-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="compression">
<section id="section-3.3">
        <h3 id="name-compression">
<a href="#section-3.3" class="section-number selfRef">3.3. </a><a href="#name-compression" class="section-name selfRef">Compression</a>
        </h3>
<div id="rec-compress">
<p id="section-3.3-1">In order to help prevent compression-related attacks (summarized in <span><a href="https://www.rfc-editor.org/rfc/rfc7457#section-2.6" class="relref">Section 2.6</a> of [<a href="#RFC7457" class="cite xref">RFC7457</a>]</span>) when using TLS 1.2, implementations and deployments <span class="bcp14">SHOULD NOT</span> support
TLS-level compression (<span><a href="https://www.rfc-editor.org/rfc/rfc5246#section-6.2.2" class="relref">Section 6.2.2</a> of [<a href="#RFC5246" class="cite xref">RFC5246</a>]</span>); the only exception is when
the application protocol in question has been proven not to be open to such attacks.
However, even in this case, extreme caution is warranted because of the potential for
 future attacks related to TLS compression. More specifically, the HTTP protocol is known to be vulnerable to compression-related attacks. (This recommendation applies to TLS 1.2 only, because compression has been removed from TLS 1.3.)<a href="#section-3.3-1" class="pilcrow">¶</a></p>
</div>
<p id="section-3.3-2">Rationale: TLS compression has been subject to security attacks such as the Compression Ratio Info-leak Made Easy (CRIME) attack.<a href="#section-3.3-2" class="pilcrow">¶</a></p>
<p id="section-3.3-3">Implementers should note that compression at higher protocol levels can allow an active attacker to extract cleartext information from the connection. The Browser Reconnaissance and Exfiltration via Adaptive Compression of Hypertext (BREACH) attack is one such case. These issues can only be mitigated outside of TLS and are thus outside the scope of this document. See <span><a href="https://www.rfc-editor.org/rfc/rfc7457#section-2.6" class="relref">Section 2.6</a> of [<a href="#RFC7457" class="cite xref">RFC7457</a>]</span> for further details.<a href="#section-3.3-3" class="pilcrow">¶</a></p>
<div id="certificate-compression">
<section id="section-3.3.1">
          <h4 id="name-certificate-compression">
<a href="#section-3.3.1" class="section-number selfRef">3.3.1. </a><a href="#name-certificate-compression" class="section-name selfRef">Certificate Compression</a>
          </h4>
<p id="section-3.3.1-1">Certificate chains often take up most of the bytes transmitted during
the handshake.  In order to manage their size, some or all of the following
methods can be employed (see also <span><a href="https://www.rfc-editor.org/rfc/rfc9191#section-4" class="relref">Section 4</a> of [<a href="#RFC9191" class="cite xref">RFC9191</a>]</span> for further suggestions):<a href="#section-3.3.1-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-3.3.1-2.1">Limit the number of names or extensions.<a href="#section-3.3.1-2.1" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-3.3.1-2.2">Use keys with small public key representations, like the Elliptic Curve Digital Signature Algorithm (ECDSA).<a href="#section-3.3.1-2.2" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-3.3.1-2.3">Use certificate compression.<a href="#section-3.3.1-2.3" class="pilcrow">¶</a>
</li>
          </ul>
<p id="section-3.3.1-3">To achieve the latter, TLS 1.3 defines the <code>compress_certificate</code> extension in
<span>[<a href="#RFC8879" class="cite xref">RFC8879</a>]</span>.  See also <span><a href="https://www.rfc-editor.org/rfc/rfc8879#section-5" class="relref">Section 5</a> of [<a href="#RFC8879" class="cite xref">RFC8879</a>]</span> for security and privacy
considerations associated with its use.  For the avoidance of doubt, CRIME-style attacks on TLS
compression do not apply to certificate compression.<a href="#section-3.3.1-3" class="pilcrow">¶</a></p>
<p id="section-3.3.1-4">Due to the strong likelihood of middlebox interference,
compression in the style of <span>[<a href="#RFC8879" class="cite xref">RFC8879</a>]</span> has not been made available in
TLS 1.2.  In theory, the <code>cached_info</code> extension defined in <span>[<a href="#RFC7924" class="cite xref">RFC7924</a>]</span> could
be used, but it is not supported widely enough to be considered a practical
alternative.<a href="#section-3.3.1-4" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="rec-resume">
<section id="section-3.4">
        <h3 id="name-tls-session-resumption">
<a href="#section-3.4" class="section-number selfRef">3.4. </a><a href="#name-tls-session-resumption" class="section-name selfRef">TLS Session Resumption</a>
        </h3>
<p id="section-3.4-1">Session resumption drastically reduces the number of full TLS handshakes and thus is an essential
performance feature for most deployments.<a href="#section-3.4-1" class="pilcrow">¶</a></p>
<p id="section-3.4-2">Stateless session resumption with session tickets is a popular strategy. For TLS 1.2, it is specified in
<span>[<a href="#RFC5077" class="cite xref">RFC5077</a>]</span>.  For TLS 1.3, a more secure mechanism based on the use of a pre-shared key (PSK) is described in
<span><a href="https://www.rfc-editor.org/rfc/rfc8446#section-4.6.1" class="relref">Section 4.6.1</a> of [<a href="#RFC8446" class="cite xref">RFC8446</a>]</span>. See <span>[<a href="#Springall16" class="cite xref">Springall16</a>]</span> for a quantitative study of the risks induced by TLS cryptographic "shortcuts", including session resumption.<a href="#section-3.4-2" class="pilcrow">¶</a></p>
<p id="section-3.4-3">When it is used, the resumption information <span class="bcp14">MUST</span>
be authenticated and encrypted to prevent modification or eavesdropping by an attacker.
Further recommendations apply to session tickets:<a href="#section-3.4-3" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-3.4-4.1">A strong cipher <span class="bcp14">MUST</span> be used when encrypting the ticket (at least as strong as the main TLS cipher suite).<a href="#section-3.4-4.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-3.4-4.2">Ticket-encryption keys <span class="bcp14">MUST</span> be changed regularly, e.g., once every week, so as not to negate the benefits of forward secrecy (see <a href="#sec-pfs" class="auto internal xref">Section 7.3</a> for details on forward secrecy). Old ticket-encryption keys <span class="bcp14">MUST</span> be destroyed at the end of the validity period.<a href="#section-3.4-4.2" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-3.4-4.3">For similar reasons, session ticket validity <span class="bcp14">MUST</span> be limited to a reasonable duration (e.g., half as long as ticket-encryption key validity).<a href="#section-3.4-4.3" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-3.4-4.4">TLS 1.2 does not roll the session key forward within a single session. Thus, to prevent an attack where the server's ticket-encryption key is stolen and used to decrypt the entire content of a session (negating the concept of forward secrecy), a TLS 1.2 server <span class="bcp14">SHOULD NOT</span> resume sessions that are too old, e.g., sessions that have been open longer than two ticket-encryption key rotation periods.<a href="#section-3.4-4.4" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-3.4-5">Rationale: Session resumption is another kind of TLS handshake and therefore must be as secure as the initial handshake. This document (<a href="#detail" class="auto internal xref">Section 4</a>) recommends the use of cipher suites that provide forward secrecy, i.e., that prevent an attacker who gains momentary access to the TLS endpoint (either client or server) and its secrets from reading either past or future communication. The tickets must be managed so as not to negate this security property.<a href="#section-3.4-5" class="pilcrow">¶</a></p>
<p id="section-3.4-6">TLS 1.3 provides the powerful option of forward secrecy even within a long-lived connection
that is periodically resumed. <span><a href="https://www.rfc-editor.org/rfc/rfc8446#section-2.2" class="relref">Section 2.2</a> of [<a href="#RFC8446" class="cite xref">RFC8446</a>]</span> recommends that clients <span class="bcp14">SHOULD</span>
send a "key_share" when initiating session resumption.
In order to gain forward secrecy, this document recommends that server implementations <span class="bcp14">SHOULD</span>
select the "psk_dhe_ke" PSK key exchange mode and 
respond with a "key_share" to complete an Ephemeral Elliptic Curve Diffie-Hellman (ECDHE) exchange on each session resumption.
As a more performant alternative, server implementations <span class="bcp14">MAY</span> refrain from responding with a 
"key_share" until a certain amount of time (e.g., measured in hours) has passed since the last 
ECDHE exchange; this implies that the "key_share" operation would not occur for the presumed
majority of session resumption requests (which would occur within a few hours) while still ensuring 
forward secrecy for longer-lived sessions.<a href="#section-3.4-6" class="pilcrow">¶</a></p>
<p id="section-3.4-7">TLS session resumption introduces potential privacy issues where the server is able
to track the client, in some cases indefinitely. See <span>[<a href="#Sy2018" class="cite xref">Sy2018</a>]</span> for more details.<a href="#section-3.4-7" class="pilcrow">¶</a></p>
</section>
</div>
<div id="renegotiation-in-tls-12">
<section id="section-3.5">
        <h3 id="name-renegotiation-in-tls-12">
<a href="#section-3.5" class="section-number selfRef">3.5. </a><a href="#name-renegotiation-in-tls-12" class="section-name selfRef">Renegotiation in TLS 1.2</a>
        </h3>
<p id="section-3.5-1">The recommendations in this section apply to TLS 1.2 only, because renegotiation has been removed from TLS 1.3.<a href="#section-3.5-1" class="pilcrow">¶</a></p>
<p id="section-3.5-2">Renegotiation in TLS 1.2 is a handshake that establishes new cryptographic parameters for an existing session. The mechanism existed in TLS 1.2 and in earlier protocol versions and was improved following several major attacks including a plaintext injection attack, CVE-2009-3555 <span>[<a href="#CVE" class="cite xref">CVE</a>]</span>.<a href="#section-3.5-2" class="pilcrow">¶</a></p>
<p id="section-3.5-3">TLS 1.2 clients and servers <span class="bcp14">MUST</span> implement the <code>renegotiation_info</code> extension, as defined in <span>[<a href="#RFC5746" class="cite xref">RFC5746</a>]</span>.<a href="#section-3.5-3" class="pilcrow">¶</a></p>
<p id="section-3.5-4">TLS 1.2 clients <span class="bcp14">MUST</span> send <code>renegotiation_info</code> in the Client Hello.  If the server does not acknowledge the extension, the client <span class="bcp14">MUST</span> generate a fatal <code>handshake_failure</code> alert prior to terminating the connection.<a href="#section-3.5-4" class="pilcrow">¶</a></p>
<p id="section-3.5-5">Rationale: It is not safe for a client to connect to a TLS 1.2 server that does not support <code>renegotiation_info</code> regardless of whether either endpoint actually implements renegotiation.  See also <span><a href="https://www.rfc-editor.org/rfc/rfc5746#section-4.1" class="relref">Section 4.1</a> of [<a href="#RFC5746" class="cite xref">RFC5746</a>]</span>.<a href="#section-3.5-5" class="pilcrow">¶</a></p>
<p id="section-3.5-6">A related attack resulting from TLS session parameters not being properly authenticated is a Triple Handshake <span>[<a href="#Triple-Handshake" class="cite xref">Triple-Handshake</a>]</span>. To address this attack, TLS 1.2 implementations <span class="bcp14">MUST</span> support the <code>extended_master_secret</code> extension defined in <span>[<a href="#RFC7627" class="cite xref">RFC7627</a>]</span>.<a href="#section-3.5-6" class="pilcrow">¶</a></p>
</section>
</div>
<div id="post-handshake-authentication">
<section id="section-3.6">
        <h3 id="name-post-handshake-authenticati">
<a href="#section-3.6" class="section-number selfRef">3.6. </a><a href="#name-post-handshake-authenticati" class="section-name selfRef">Post-Handshake Authentication</a>
        </h3>
<p id="section-3.6-1">Renegotiation in TLS 1.2 was (partially) replaced in TLS 1.3 by separate post-handshake authentication and key update mechanisms.  In the context of protocols that multiplex requests over a single connection (such as HTTP/2 <span>[<a href="#RFC9113" class="cite xref">RFC9113</a>]</span>), post-handshake authentication has the same problems as TLS 1.2 renegotiation. Multiplexed protocols <span class="bcp14">SHOULD</span> follow the advice provided for HTTP/2 in <span><a href="https://www.rfc-editor.org/rfc/rfc9113#section-9.2.3" class="relref">Section 9.2.3</a> of [<a href="#RFC9113" class="cite xref">RFC9113</a>]</span>.<a href="#section-3.6-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="sni">
<section id="section-3.7">
        <h3 id="name-server-name-indication-sni">
<a href="#section-3.7" class="section-number selfRef">3.7. </a><a href="#name-server-name-indication-sni" class="section-name selfRef">Server Name Indication (SNI)</a>
        </h3>
<p id="section-3.7-1">TLS implementations <span class="bcp14">MUST</span> support the Server Name Indication (SNI) extension defined in <span><a href="https://www.rfc-editor.org/rfc/rfc6066#section-3" class="relref">Section 3</a> of [<a href="#RFC6066" class="cite xref">RFC6066</a>]</span> for those higher-level protocols that would benefit from it, including HTTPS. However, the actual use of SNI in particular circumstances is a matter of local policy.  At the time of writing, a technology for encrypting the SNI (called Encrypted Client Hello) is being worked on in the TLS Working Group <span>[<a href="#I-D.ietf-tls-esni" class="cite xref">TLS-ECH</a>]</span>.  Once that method has been standardized and widely implemented, it will likely be appropriate to recommend its usage in a future version of this BCP.<a href="#section-3.7-1" class="pilcrow">¶</a></p>
<p id="section-3.7-2">Rationale: SNI supports deployment of multiple TLS-protected virtual servers on a single
      address, and therefore enables fine-grained security for these virtual servers,
      by allowing each one to have its own certificate. However, SNI also leaks the 
      target domain for a given connection; this information leak will be closed by 
      use of TLS Encrypted Client Hello once that method has been standardized.<a href="#section-3.7-2" class="pilcrow">¶</a></p>
<p id="section-3.7-3">In order to prevent the attacks described in <span>[<a href="#ALPACA" class="cite xref">ALPACA</a>]</span>, a server that does not
recognize the presented server name <span class="bcp14">SHOULD NOT</span> continue the handshake and
instead <span class="bcp14">SHOULD</span> fail with a fatal-level <code>unrecognized_name(112)</code> alert.  Note that this
recommendation updates <span><a href="https://www.rfc-editor.org/rfc/rfc6066#section-3" class="relref">Section 3</a> of [<a href="#RFC6066" class="cite xref">RFC6066</a>]</span>, which stated:<a href="#section-3.7-3" class="pilcrow">¶</a></p>
<blockquote id="section-3.7-4">If the server understood the
ClientHello extension but does not recognize the server name, the server <span class="bcp14">SHOULD</span>
take one of two actions: either abort the handshake by sending a fatal-level
<code>unrecognized_name(112)</code> alert or continue the handshake.<a href="#section-3.7-4" class="pilcrow">¶</a>
</blockquote>
<p id="section-3.7-5"> 
Clients <span class="bcp14">SHOULD</span> abort the handshake if the server acknowledges the SNI extension but presents a certificate with a different hostname than the one sent by the client.<a href="#section-3.7-5" class="pilcrow">¶</a></p>
</section>
</div>
<div id="rec-alpn">
<section id="section-3.8">
        <h3 id="name-application-layer-protocol-">
<a href="#section-3.8" class="section-number selfRef">3.8. </a><a href="#name-application-layer-protocol-" class="section-name selfRef">Application-Layer Protocol Negotiation (ALPN)</a>
        </h3>
<p id="section-3.8-1">TLS implementations (both client- and server-side) <span class="bcp14">MUST</span> support the
Application-Layer Protocol Negotiation (ALPN) extension <span>[<a href="#RFC7301" class="cite xref">RFC7301</a>]</span>.<a href="#section-3.8-1" class="pilcrow">¶</a></p>
<p id="section-3.8-2">In order to prevent "cross-protocol" attacks resulting from failure to ensure
that a message intended for use in one protocol cannot be mistaken for a
message for use in another protocol, servers are advised to strictly enforce the
behavior prescribed in <span><a href="https://www.rfc-editor.org/rfc/rfc7301#section-3.2" class="relref">Section 3.2</a> of [<a href="#RFC7301" class="cite xref">RFC7301</a>]</span>:<a href="#section-3.8-2" class="pilcrow">¶</a></p>
<blockquote id="section-3.8-3"> In the event that the
server supports no protocols that the client advertises, then the server <span class="bcp14">SHALL</span>
respond with a fatal '<code>no_application_protocol</code>' alert.<a href="#section-3.8-3" class="pilcrow">¶</a>
</blockquote>
<p id="section-3.8-4">
Clients <span class="bcp14">SHOULD</span>
abort the handshake if the server acknowledges the ALPN extension
but does not select a protocol from the client list.  Failure to do so can
result in attacks such those described in <span>[<a href="#ALPACA" class="cite xref">ALPACA</a>]</span>.<a href="#section-3.8-4" class="pilcrow">¶</a></p>
<p id="section-3.8-5">Protocol developers are strongly encouraged to register an ALPN identifier 
for their protocols. This applies both to new protocols and to well-established 
protocols; however, because the latter might have a large deployed base,
strict enforcement of ALPN usage may not be feasible when an ALPN 
identifier is registered for a well-established protocol.<a href="#section-3.8-5" class="pilcrow">¶</a></p>
</section>
</div>
<div id="multi-server-deployment">
<section id="section-3.9">
        <h3 id="name-multi-server-deployment">
<a href="#section-3.9" class="section-number selfRef">3.9. </a><a href="#name-multi-server-deployment" class="section-name selfRef">Multi-Server Deployment</a>
        </h3>
<p id="section-3.9-1">Deployments that involve multiple servers or services can increase the size of the attack surface for TLS. Two scenarios are of interest:<a href="#section-3.9-1" class="pilcrow">¶</a></p>
<ol start="1" type="1" class="normal type-1" id="section-3.9-2">
<li id="section-3.9-2.1">Deployments in which multiple services handle the same domain name via different 
protocols (e.g., HTTP and IMAP). In this case, an attacker might be able to direct 
a connecting endpoint to the service offering a different protocol and mount a 
cross-protocol attack. In a cross-protocol attack, the client and server believe 
they are using different protocols, which the attacker might exploit if messages 
sent in one protocol are interpreted as messages in the other protocol with 
undesirable effects (see <span>[<a href="#ALPACA" class="cite xref">ALPACA</a>]</span> for more detailed information about this class 
of attacks). To mitigate this threat, service providers <span class="bcp14">SHOULD</span> deploy ALPN (see
<a href="#rec-alpn" class="auto internal xref">Section 3.8</a>). In addition, to the extent possible, they <span class="bcp14">SHOULD</span> ensure that multiple 
services handling the same domain name provide equivalent levels of security that are consistent with the recommendations in this document; such measures <span class="bcp14">SHOULD</span> include the handling of configurations across multiple TLS servers and protections against compromise of credentials held by those servers.<a href="#section-3.9-2.1" class="pilcrow">¶</a>
</li>
          <li id="section-3.9-2.2">Deployments in which multiple servers providing the same service have different
TLS configurations. In this case, an attacker might be able to direct a connecting 
endpoint to a server with a TLS configuration that is more easily exploitable (see 
<span>[<a href="#DROWN" class="cite xref">DROWN</a>]</span> for more detailed information about this class of attacks). To mitigate 
this threat, service providers <span class="bcp14">SHOULD</span> ensure that all servers providing the same 
service provide equivalent levels of security that are consistent with the 
recommendations in this document.<a href="#section-3.9-2.2" class="pilcrow">¶</a>
</li>
        </ol>
</section>
</div>
<div id="zero-round-trip-time-0-rtt-data-in-tls-13">
<section id="section-3.10">
        <h3 id="name-zero-round-trip-time-0-rtt-">
<a href="#section-3.10" class="section-number selfRef">3.10. </a><a href="#name-zero-round-trip-time-0-rtt-" class="section-name selfRef">Zero Round-Trip Time (0-RTT) Data in TLS 1.3</a>
        </h3>
<p id="section-3.10-1">The 0-RTT early data feature is new in TLS 1.3. It provides reduced latency
when TLS connections are resumed, at the potential cost of certain security properties.
As a result, it requires special attention from implementers on both
the server and the client side. Typically, this extends to the
TLS library as well as protocol layers above it.<a href="#section-3.10-1" class="pilcrow">¶</a></p>
<p id="section-3.10-2">For HTTP over TLS, refer to <span>[<a href="#RFC8470" class="cite xref">RFC8470</a>]</span> for guidance.<a href="#section-3.10-2" class="pilcrow">¶</a></p>
<p id="section-3.10-3">For QUIC on TLS, refer to <span><a href="https://www.rfc-editor.org/rfc/rfc9001#section-9.2" class="relref">Section 9.2</a> of [<a href="#RFC9001" class="cite xref">RFC9001</a>]</span>.<a href="#section-3.10-3" class="pilcrow">¶</a></p>
<p id="section-3.10-4">For other protocols, generic guidance is given in Section <a href="https://www.rfc-editor.org/rfc/rfc8446#section-8" class="relref">8</a> and Appendix <a href="https://www.rfc-editor.org/rfc/rfc8446#appendix-E.5" class="relref">E.5</a> of <span>[<a href="#RFC8446" class="cite xref">RFC8446</a>]</span>.
To paraphrase Appendix <a href="https://www.rfc-editor.org/rfc/rfc8446#appendix-E.5" class="relref">E.5</a>, applications <span class="bcp14">MUST</span> avoid this feature unless
an explicit specification exists for the application protocol in question to clarify
when 0-RTT is appropriate and secure. This can take the form of an IETF RFC,
a non-IETF standard, or documentation associated with a non-standard protocol.<a href="#section-3.10-4" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="detail">
<section id="section-4">
      <h2 id="name-recommendations-cipher-suit">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-recommendations-cipher-suit" class="section-name selfRef">Recommendations: Cipher Suites</a>
      </h2>
<p id="section-4-1">TLS 1.2 provided considerable flexibility in the selection of cipher suites. Unfortunately, the security of some of these cipher suites has degraded over time to the point where some are known to be insecure (this is one reason why TLS 1.3 restricted such flexibility). Incorrectly configuring a server leads to no or reduced security.  This section includes recommendations on the selection and negotiation of cipher suites.<a href="#section-4-1" class="pilcrow">¶</a></p>
<div id="rec-cipher-guidelines">
<section id="section-4.1">
        <h3 id="name-general-guidelines">
<a href="#section-4.1" class="section-number selfRef">4.1. </a><a href="#name-general-guidelines" class="section-name selfRef">General Guidelines</a>
        </h3>
<p id="section-4.1-1">Cryptographic algorithms weaken over time as cryptanalysis improves: algorithms that were once considered strong become weak. Consequently, cipher suites using weak algorithms need to be phased out and replaced with more secure cipher suites. This helps to ensure that the desired security properties still hold. SSL/TLS has been in existence for well over 20 years and many of the cipher suites that have been recommended in various versions of SSL/TLS are now considered weak or at least not as strong as desired. Therefore, this section modernizes the recommendations concerning cipher suite selection.<a href="#section-4.1-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4.1-2.1">
            <p id="section-4.1-2.1.1">Implementations <span class="bcp14">MUST NOT</span> negotiate the cipher suites with NULL encryption.<a href="#section-4.1-2.1.1" class="pilcrow">¶</a></p>
<p id="section-4.1-2.1.2">
Rationale: The NULL cipher suites do not encrypt traffic and 
             so provide no confidentiality services. Any entity in the 
             network with access to the connection can view the plaintext 
             of contents being exchanged by the client and server. Nevertheless, this document does not discourage software from
             implementing NULL cipher suites, since they can be useful for 
             testing and debugging.<a href="#section-4.1-2.1.2" class="pilcrow">¶</a></p>
</li>
          <li class="normal" id="section-4.1-2.2">
            <p id="section-4.1-2.2.1">Implementations <span class="bcp14">MUST NOT</span> negotiate RC4 cipher suites.<a href="#section-4.1-2.2.1" class="pilcrow">¶</a></p>
<p id="section-4.1-2.2.2">
Rationale: The RC4 stream cipher has a variety of cryptographic 
             weaknesses, as documented in <span>[<a href="#RFC7465" class="cite xref">RFC7465</a>]</span>.
     Note that DTLS specifically forbids the use of RC4 already.<a href="#section-4.1-2.2.2" class="pilcrow">¶</a></p>
</li>
          <li class="normal" id="section-4.1-2.3">
            <p id="section-4.1-2.3.1">Implementations <span class="bcp14">MUST NOT</span> negotiate cipher suites offering less 
             than 112 bits of security, including so-called "export-level" 
             encryption (which provides 40 or 56 bits of security).<a href="#section-4.1-2.3.1" class="pilcrow">¶</a></p>
<p id="section-4.1-2.3.2">
Rationale: Based on <span>[<a href="#RFC3766" class="cite xref">RFC3766</a>]</span>, at least 112 bits 
             of security is needed.  40-bit and 56-bit security (found in 
             so-called "export ciphers") are considered 
             insecure today.<a href="#section-4.1-2.3.2" class="pilcrow">¶</a></p>
</li>
          <li class="normal" id="section-4.1-2.4">
            <p id="section-4.1-2.4.1">Implementations <span class="bcp14">SHOULD NOT</span> negotiate cipher suites that use 
             algorithms offering less than 128 bits of security.<a href="#section-4.1-2.4.1" class="pilcrow">¶</a></p>
<p id="section-4.1-2.4.2">
Rationale: Cipher suites that offer 112 or more bits but less than 128 bits
             of security are not considered weak at this time; however, it is 
             expected that their useful lifespan is short enough to justify 
             supporting stronger cipher suites at this time.  128-bit ciphers 
             are expected to remain secure for at least several years and 
             256-bit ciphers until the next fundamental technology 
             breakthrough.  Note that, because of so-called 
             "meet-in-the-middle" attacks <span>[<a href="#Multiple-Encryption" class="cite xref">Multiple-Encryption</a>]</span>,
             some legacy cipher suites (e.g., 168-bit Triple DES (3DES)) have an effective 
             key length that is smaller than their nominal key length (112 
             bits in the case of 3DES).  Such cipher suites should be 
             evaluated according to their effective key length.<a href="#section-4.1-2.4.2" class="pilcrow">¶</a></p>
</li>
          <li class="normal" id="section-4.1-2.5">
            <p id="section-4.1-2.5.1">Implementations <span class="bcp14">SHOULD NOT</span> negotiate cipher suites based on 
             RSA key transport, a.k.a. "static RSA".<a href="#section-4.1-2.5.1" class="pilcrow">¶</a></p>
<p id="section-4.1-2.5.2">
Rationale: These cipher suites, which have assigned values starting 
             with the string "TLS_RSA_WITH_*", have several drawbacks, especially
             the fact that they do not support forward secrecy.<a href="#section-4.1-2.5.2" class="pilcrow">¶</a></p>
</li>
          <li class="normal" id="section-4.1-2.6">
            <p id="section-4.1-2.6.1">Implementations <span class="bcp14">SHOULD NOT</span> negotiate cipher suites based on
             non-ephemeral (static) finite-field Diffie-Hellman (DH) key agreement. Similarly, implementations <span class="bcp14">SHOULD NOT</span> negotiate non-ephemeral Elliptic Curve DH key agreement.<a href="#section-4.1-2.6.1" class="pilcrow">¶</a></p>
<p id="section-4.1-2.6.2">
Rationale: The former cipher suites, which have assigned values prefixed by "TLS_DH_*", have several drawbacks, especially
             the fact that they do not support forward secrecy. The latter ("TLS_ECDH_*") also lack forward secrecy and are subject to invalid curve attacks <span>[<a href="#Jager2015" class="cite xref">Jager2015</a>]</span>.<a href="#section-4.1-2.6.2" class="pilcrow">¶</a></p>
</li>
          <li class="normal" id="section-4.1-2.7">
            <p id="section-4.1-2.7.1">Implementations <span class="bcp14">MUST</span> support and prefer to negotiate cipher suites 
             offering forward secrecy.  However, TLS 1.2 implementations <span class="bcp14">SHOULD NOT</span> negotiate
             cipher suites based on ephemeral finite-field Diffie-Hellman key
             agreement (i.e., "TLS_DHE_*" suites).  This is justified by the known fragility
             of the construction (see <span>[<a href="#RACCOON" class="cite xref">RACCOON</a>]</span>) and the limitation around
             negotiation, including using <span>[<a href="#RFC7919" class="cite xref">RFC7919</a>]</span>, which has seen very
             limited uptake.<a href="#section-4.1-2.7.1" class="pilcrow">¶</a></p>
<p id="section-4.1-2.7.2">
Rationale: Forward secrecy (sometimes called "perfect forward 
             secrecy") prevents the recovery of information that was encrypted 
             with older session keys, thus limiting how far back in time data
             can be decrypted when an attack is successful.  See Sections <a href="#sec-pfs" class="auto internal xref">7.3</a>
             and <a href="#sec-dhe" class="auto internal xref">7.4</a> for a detailed discussion.<a href="#section-4.1-2.7.2" class="pilcrow">¶</a></p>
</li>
        </ul>
</section>
</div>
<div id="rec-cipher">
<section id="section-4.2">
        <h3 id="name-cipher-suites-for-tls-12">
<a href="#section-4.2" class="section-number selfRef">4.2. </a><a href="#name-cipher-suites-for-tls-12" class="section-name selfRef">Cipher Suites for TLS 1.2</a>
        </h3>
<p id="section-4.2-1">Given the foregoing considerations, implementation and deployment of the following cipher suites is <span class="bcp14">RECOMMENDED</span>:<a href="#section-4.2-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4.2-2.1">TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256<a href="#section-4.2-2.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.2-2.2">TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384<a href="#section-4.2-2.2" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.2-2.3">TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256<a href="#section-4.2-2.3" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.2-2.4">TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384<a href="#section-4.2-2.4" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-4.2-3">As these are Authenticated Encryption with Associated Data (AEAD) algorithms <span>[<a href="#RFC5116" class="cite xref">RFC5116</a>]</span>, these cipher suites are supported only in TLS 1.2 and not in earlier protocol versions.<a href="#section-4.2-3" class="pilcrow">¶</a></p>
<p id="section-4.2-4">Typically, to prefer these suites, the order of suites needs to be explicitly configured in server software.  It would be ideal if server software implementations were to prefer these suites by default.<a href="#section-4.2-4" class="pilcrow">¶</a></p>
<p id="section-4.2-5">Some devices have hardware support for AES Counter Mode with CBC-MAC (AES-CCM) but not AES Galois/Counter Mode (AES-GCM), so they are unable to follow the foregoing recommendations regarding cipher suites.  There are even devices that do not support public key cryptography at all, but these are out of scope entirely.<a href="#section-4.2-5" class="pilcrow">¶</a></p>
<p id="section-4.2-6">A cipher suite that operates in CBC (cipher block chaining) mode (e.g.,
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) <span class="bcp14">SHOULD NOT</span> be used unless the
<code>encrypt_then_mac</code> extension <span>[<a href="#RFC7366" class="cite xref">RFC7366</a>]</span> is also successfully negotiated.
This requirement applies to both client and server implementations.<a href="#section-4.2-6" class="pilcrow">¶</a></p>
<p id="section-4.2-7">When using ECDSA signatures for authentication of TLS peers, it is <span class="bcp14">RECOMMENDED</span> that implementations use the NIST curve P-256. In addition, to avoid predictable or repeated nonces (which could reveal the long-term signing key), it is <span class="bcp14">RECOMMENDED</span> that implementations implement "deterministic ECDSA" as specified in <span>[<a href="#RFC6979" class="cite xref">RFC6979</a>]</span> and in line with the recommendations in <span>[<a href="#RFC8446" class="cite xref">RFC8446</a>]</span>.<a href="#section-4.2-7" class="pilcrow">¶</a></p>
<p id="section-4.2-8">Note that implementations of "deterministic ECDSA" may be vulnerable to certain
side-channel and fault injection attacks precisely because of their
determinism.  While most fault injection attacks described in the literature assume
physical access to the device (and therefore are more relevant in Internet of Things (IoT)
deployments with poor or non-existent physical security), some can be carried
out remotely <span>[<a href="#Poddebniak2017" class="cite xref">Poddebniak2017</a>]</span>, e.g., as Rowhammer <span>[<a href="#Kim2014" class="cite xref">Kim2014</a>]</span> variants.  In
deployments where side-channel attacks and fault injection attacks are a
concern, implementation strategies combining both randomness and determinism
(for example, as described in <span>[<a href="#I-D.mattsson-cfrg-det-sigs-with-noise" class="cite xref">CFRG-DET-SIGS</a>]</span>) can
be used to avoid the risk of successful extraction of the signing key.<a href="#section-4.2-8" class="pilcrow">¶</a></p>
<div id="detail-neg">
<section id="section-4.2.1">
          <h4 id="name-implementation-details">
<a href="#section-4.2.1" class="section-number selfRef">4.2.1. </a><a href="#name-implementation-details" class="section-name selfRef">Implementation Details</a>
          </h4>
<p id="section-4.2.1-1">Clients <span class="bcp14">SHOULD</span> include TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 as the first proposal to any server.  Servers <span class="bcp14">MUST</span> prefer this cipher suite over weaker cipher suites whenever it is proposed, even if it is not the first proposal.  Clients are of course free to offer stronger cipher suites, e.g., using AES-256; when they do, the server <span class="bcp14">SHOULD</span> prefer the stronger cipher suite unless there are compelling reasons (e.g., seriously degraded performance) to choose otherwise.<a href="#section-4.2.1-1" class="pilcrow">¶</a></p>
<p id="section-4.2.1-2">The previous version of the TLS recommendations <span>[<a href="#RFC7525" class="cite xref">RFC7525</a>]</span> implicitly allowed the old RFC 5246 mandatory-to-implement cipher suite, TLS_RSA_WITH_AES_128_CBC_SHA. At the time of writing, this cipher suite does not provide additional interoperability, except with very old clients. As with other cipher suites that do not provide forward secrecy, implementations <span class="bcp14">SHOULD NOT</span> support this cipher suite. Other application protocols specify other cipher suites as mandatory to implement (MTI).<a href="#section-4.2.1-2" class="pilcrow">¶</a></p>
<p id="section-4.2.1-3"><span>[<a href="#RFC8422" class="cite xref">RFC8422</a>]</span> allows clients and servers to negotiate ECDH parameters (curves). Both clients and servers <span class="bcp14">SHOULD</span> include the "Supported Elliptic Curves Extension" <span>[<a href="#RFC8422" class="cite xref">RFC8422</a>]</span>.  Clients and servers <span class="bcp14">SHOULD</span> support the NIST P‑256 (secp256r1) <span>[<a href="#RFC8422" class="cite xref">RFC8422</a>]</span> and X25519 (x25519) <span>[<a href="#RFC7748" class="cite xref">RFC7748</a>]</span> curves.  Note that <span>[<a href="#RFC8422" class="cite xref">RFC8422</a>]</span> deprecates all but the uncompressed point format.  Therefore, if the client sends an <code>ec_point_formats</code> extension, the ECPointFormatList <span class="bcp14">MUST</span> contain a single element, "uncompressed".<a href="#section-4.2.1-3" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="cipher-suites-for-tls-13">
<section id="section-4.3">
        <h3 id="name-cipher-suites-for-tls-13">
<a href="#section-4.3" class="section-number selfRef">4.3. </a><a href="#name-cipher-suites-for-tls-13" class="section-name selfRef">Cipher Suites for TLS 1.3</a>
        </h3>
<p id="section-4.3-1">This document does not specify any cipher suites for TLS 1.3. Readers
are referred to <span><a href="https://www.rfc-editor.org/rfc/rfc8446#section-9.1" class="relref">Section 9.1</a> of [<a href="#RFC8446" class="cite xref">RFC8446</a>]</span> for cipher suite recommendations.<a href="#section-4.3-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="limits-on-key-usage">
<section id="section-4.4">
        <h3 id="name-limits-on-key-usage">
<a href="#section-4.4" class="section-number selfRef">4.4. </a><a href="#name-limits-on-key-usage" class="section-name selfRef">Limits on Key Usage</a>
        </h3>
<p id="section-4.4-1">All ciphers have an upper limit on the amount of traffic that can be securely
protected with any given key. In the case of AEAD cipher suites, two separate
limits are maintained for each key:<a href="#section-4.4-1" class="pilcrow">¶</a></p>
<ol start="1" type="1" class="normal type-1" id="section-4.4-2">
<li id="section-4.4-2.1">Confidentiality limit (CL), i.e., the number of records that can be
encrypted.<a href="#section-4.4-2.1" class="pilcrow">¶</a>
</li>
          <li id="section-4.4-2.2">Integrity limit (IL), i.e., the number of records that are allowed to fail
authentication.<a href="#section-4.4-2.2" class="pilcrow">¶</a>
</li>
        </ol>
<p id="section-4.4-3">The latter applies to DTLS (and also to QUIC) but not to TLS itself, since TLS connections are torn down on the
first decryption failure.<a href="#section-4.4-3" class="pilcrow">¶</a></p>
<p id="section-4.4-4">When a sender is approaching CL, the implementation <span class="bcp14">SHOULD</span> initiate a new handshake (in TLS 1.3, this can be achieved by sending a KeyUpdate message on the established session) to rotate the session key. When a receiver has reached IL, the implementation <span class="bcp14">SHOULD</span> close the connection. Although these recommendations are a best practice, implementers need to be aware that it is not always easy to accomplish them in protocols that are built on top of TLS/DTLS without introducing coordination across layer boundaries.  See <span><a href="https://www.rfc-editor.org/rfc/rfc9001#section-6" class="relref">Section 6</a> of [<a href="#RFC9001" class="cite xref">RFC9001</a>]</span> for an example of the cooperation that was necessary in QUIC between the crypto and transport layers to support key updates.  Note that in general, application protocols might not be able to emulate that method given their more constrained interaction with TLS/DTLS. As a result of these complexities, these recommendations are not mandatory.<a href="#section-4.4-4" class="pilcrow">¶</a></p>
<p id="section-4.4-5">For all TLS 1.3 cipher suites, readers are referred to <span><a href="https://www.rfc-editor.org/rfc/rfc8446#section-5.5" class="relref">Section 5.5</a> of [<a href="#RFC8446" class="cite xref">RFC8446</a>]</span> for the values of CL and IL. For all DTLS 1.3 cipher suites, readers are referred to <span><a href="https://www.rfc-editor.org/rfc/rfc9147#section-4.5.3" class="relref">Section 4.5.3</a> of [<a href="#RFC9147" class="cite xref">RFC9147</a>]</span>.<a href="#section-4.4-5" class="pilcrow">¶</a></p>
<p id="section-4.4-6">For all AES-GCM cipher suites recommended for TLS 1.2 and DTLS 1.2 in this
document, CL can be derived by plugging the corresponding parameters into the
inequalities in <span><a href="https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-aead-limits-05#section-6.1" class="relref">Section 6.1</a> of [<a href="#I-D.irtf-cfrg-aead-limits" class="cite xref">AEAD-LIMITS</a>]</span> that apply to
random, partially implicit nonces, i.e., the nonce construction used in TLS
1.2.  Although the obtained figures are slightly higher than those for TLS 1.3,
it is <span class="bcp14">RECOMMENDED</span> that the same limit of 2<sup>24.5</sup> records is used for
both versions.<a href="#section-4.4-6" class="pilcrow">¶</a></p>
<p id="section-4.4-7">For all AES-GCM cipher suites recommended for DTLS 1.2, IL (obtained from the
same inequalities referenced above) is 2<sup>28</sup>.<a href="#section-4.4-7" class="pilcrow">¶</a></p>
</section>
</div>
<div id="rec-keylength">
<section id="section-4.5">
        <h3 id="name-public-key-length">
<a href="#section-4.5" class="section-number selfRef">4.5. </a><a href="#name-public-key-length" class="section-name selfRef">Public Key Length</a>
        </h3>
<p id="section-4.5-1">When using the cipher suites recommended in this document, two public keys are 
      normally used in the TLS handshake: one for the Diffie-Hellman key agreement
      and one for server authentication. Where a client certificate is used, a third 
      public key is added.<a href="#section-4.5-1" class="pilcrow">¶</a></p>
<p id="section-4.5-2">With a key exchange based on modular exponential (MODP) Diffie-Hellman groups ("DHE" cipher suites), DH key lengths of at least 2048 bits are <span class="bcp14">REQUIRED</span>.<a href="#section-4.5-2" class="pilcrow">¶</a></p>
<p id="section-4.5-3">Rationale: For various reasons, in practice, DH keys are typically generated in lengths
 that are powers of two (e.g., 2<sup>10</sup> = 1024 bits, 2<sup>11</sup> = 2048 bits, 2<sup>12</sup> = 4096 bits).
 Because a DH key of 1228 bits would be roughly equivalent to only an 80-bit symmetric key
<span>[<a href="#RFC3766" class="cite xref">RFC3766</a>]</span>, it is better to use keys longer than that for the "DHE" family of cipher suites.
A DH key of 1926 bits would be roughly equivalent to a 100-bit symmetric key <span>[<a href="#RFC3766" class="cite xref">RFC3766</a>]</span>.
A DH key of 2048 bits (equivalent to a 112-bit symmetric key) 
is the minimum allowed by the latest revision of <span>[<a href="#NIST.SP.800-56A" class="cite xref">NIST.SP.800-56A</a>]</span> as of this writing
(see in particular  Appendix D of that document).<a href="#section-4.5-3" class="pilcrow">¶</a></p>
<p id="section-4.5-4">As noted in <span>[<a href="#RFC3766" class="cite xref">RFC3766</a>]</span>, correcting for the emergence of The Weizmann Institute Relation Locator (TWIRL) machine <span>[<a href="#TWIRL" class="cite xref">TWIRL</a>]</span> would imply that 1024-bit DH keys yield about 61 bits of equivalent strength and that a 2048-bit DH key would yield about 92 bits of equivalent strength.
The Logjam attack <span>[<a href="#Logjam" class="cite xref">Logjam</a>]</span> further demonstrates that 1024-bit Diffie-Hellman parameters
should be avoided.<a href="#section-4.5-4" class="pilcrow">¶</a></p>
<p id="section-4.5-5">With regard to ECDH keys, implementers are referred to the IANA "TLS Supported Groups" registry (formerly known as the "EC Named Curve
Registry") within the
   "Transport Layer Security (TLS) Parameters" registry <span>[<a href="#IANA_TLS" class="cite xref">IANA_TLS</a>]</span> and in particular to the "recommended"
   groups.  Curves of less than 224 bits <span class="bcp14">MUST NOT</span> be used. This recommendation is in line with the latest
revision of <span>[<a href="#NIST.SP.800-56A" class="cite xref">NIST.SP.800-56A</a>]</span>.<a href="#section-4.5-5" class="pilcrow">¶</a></p>
<p id="section-4.5-6">When using RSA, servers <span class="bcp14">MUST</span> authenticate using certificates with at least a 2048-bit modulus for the public key. In addition, the use of the SHA-256 hash algorithm is <span class="bcp14">RECOMMENDED</span> and SHA-1 or MD5 <span class="bcp14">MUST NOT</span> be used <span>[<a href="#RFC9155" class="cite xref">RFC9155</a>]</span> (for more details, see also <span>[<a href="#CAB-Baseline" class="cite xref">CAB-Baseline</a>]</span>, for which the current version at the time of writing is 1.8.4). Clients <span class="bcp14">MUST</span> indicate to servers that they request SHA-256 by using the "Signature Algorithms" extension defined in TLS 1.2. For TLS 1.3, the same requirement is already specified by <span>[<a href="#RFC8446" class="cite xref">RFC8446</a>]</span>.<a href="#section-4.5-6" class="pilcrow">¶</a></p>
<p id="section-4.5-7"></p>
</section>
</div>
<div id="truncated-hmac">
<section id="section-4.6">
        <h3 id="name-truncated-hmac">
<a href="#section-4.6" class="section-number selfRef">4.6. </a><a href="#name-truncated-hmac" class="section-name selfRef">Truncated HMAC</a>
        </h3>
<p id="section-4.6-1">Implementations <span class="bcp14">MUST NOT</span> use the Truncated HMAC Extension, defined in <span><a href="https://www.rfc-editor.org/rfc/rfc6066#section-7" class="relref">Section 7</a> of [<a href="#RFC6066" class="cite xref">RFC6066</a>]</span>.<a href="#section-4.6-1" class="pilcrow">¶</a></p>
<p id="section-4.6-2">Rationale: The extension does not apply to the AEAD
      cipher suites recommended above. However, it does apply to most other TLS cipher suites. Its use
      has been shown to be insecure in <span>[<a href="#PatersonRS11" class="cite xref">PatersonRS11</a>]</span>.<a href="#section-4.6-2" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="applicability">
<section id="section-5">
      <h2 id="name-applicability-statement">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-applicability-statement" class="section-name selfRef">Applicability Statement</a>
      </h2>
<p id="section-5-1">The recommendations of this document primarily apply to the implementation and deployment of application protocols that are most commonly used with TLS and DTLS on the Internet today.  Examples include, but are not limited to:<a href="#section-5-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-5-2.1">Web software and services that wish to protect HTTP traffic with TLS.<a href="#section-5-2.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-2.2">Email software and services that wish to protect IMAP, Post Office Protocol version 3 (POP3), or SMTP traffic with TLS.<a href="#section-5-2.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-2.3">Instant-messaging software and services that wish to protect Extensible Messaging and Presence Protocol (XMPP) or Internet Relay Chat (IRC) traffic with TLS.<a href="#section-5-2.3" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-2.4">Realtime media software and services that wish to protect Secure Realtime Transport Protocol (SRTP) traffic with DTLS.<a href="#section-5-2.4" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-5-3">This document does not modify the implementation and deployment recommendations (e.g., mandatory-to-implement cipher suites) prescribed by existing application protocols that employ TLS or DTLS. If the community that uses such an application protocol wishes to modernize its usage of TLS or DTLS to be consistent with the best practices recommended here, it needs to explicitly update the existing application protocol definition (one example is <span>[<a href="#RFC7590" class="cite xref">RFC7590</a>]</span>, which updates <span>[<a href="#RFC6120" class="cite xref">RFC6120</a>]</span>).<a href="#section-5-3" class="pilcrow">¶</a></p>
<p id="section-5-4">Designers of new application protocols developed through the Internet
  Standards Process <span>[<a href="#RFC2026" class="cite xref">RFC2026</a>]</span> are expected at minimum to conform to the best
  practices recommended here, unless they provide documentation of
  compelling reasons that would prevent such conformance (e.g.,
  widespread deployment on constrained devices that lack support for
  the necessary algorithms).<a href="#section-5-4" class="pilcrow">¶</a></p>
<p id="section-5-5">Although many of the recommendations provided here might also apply to QUIC insofar 
that it uses the TLS 1.3 handshake protocol, QUIC and other such secure transport protocols 
are out of scope of this document. For QUIC specifically, readers are 
referred to <span><a href="https://www.rfc-editor.org/rfc/rfc9001#section-9.2" class="relref">Section 9.2</a> of [<a href="#RFC9001" class="cite xref">RFC9001</a>]</span>.<a href="#section-5-5" class="pilcrow">¶</a></p>
<p id="section-5-6">This document does not address the use of TLS in constrained-node networks
<span>[<a href="#RFC7228" class="cite xref">RFC7228</a>]</span>.  For recommendations regarding the profiling of TLS and DTLS for
small devices with severe constraints on power, memory, and processing
resources, the reader is referred to <span>[<a href="#RFC7925" class="cite xref">RFC7925</a>]</span> and
<span>[<a href="#I-D.ietf-uta-tls13-iot-profile" class="cite xref">IOT-PROFILE</a>]</span>.<a href="#section-5-6" class="pilcrow">¶</a></p>
<div id="security-services">
<section id="section-5.1">
        <h3 id="name-security-services">
<a href="#section-5.1" class="section-number selfRef">5.1. </a><a href="#name-security-services" class="section-name selfRef">Security Services</a>
        </h3>
<p id="section-5.1-1">This document provides recommendations for an audience that wishes to secure their communication with TLS to achieve the following:<a href="#section-5.1-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-5.1-2">
          <dt id="section-5.1-2.1">Confidentiality:
</dt>
          <dd style="margin-left: 1.5em" id="section-5.1-2.2">all application-layer communication is encrypted with the goal   
that no party should be able to decrypt it except the intended receiver.<a href="#section-5.1-2.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-5.1-2.3">Data integrity:
</dt>
          <dd style="margin-left: 1.5em" id="section-5.1-2.4">any changes made to the communication in transit are detectable   
by the receiver.<a href="#section-5.1-2.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-5.1-2.5">Authentication:
</dt>
          <dd style="margin-left: 1.5em" id="section-5.1-2.6">an endpoint of the TLS communication is authenticated as the      
intended entity to communicate with.<a href="#section-5.1-2.6" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-5.1-3">With regard to authentication, TLS enables authentication of one or both endpoints in the communication.  In the context of opportunistic security <span>[<a href="#RFC7435" class="cite xref">RFC7435</a>]</span>, TLS is sometimes used without authentication. As discussed in <a href="#oppsec" class="auto internal xref">Section 5.2</a>, considerations for opportunistic security are not in scope for this document.<a href="#section-5.1-3" class="pilcrow">¶</a></p>
<p id="section-5.1-4">If deployers deviate from the recommendations given in this document, they need to be aware that they might lose access to one of the foregoing security services.<a href="#section-5.1-4" class="pilcrow">¶</a></p>
<p id="section-5.1-5">This document applies only to environments where confidentiality is required. It requires algorithms and configuration options that enforce secrecy of the data in transit.<a href="#section-5.1-5" class="pilcrow">¶</a></p>
<p id="section-5.1-6">This document also assumes that data integrity protection is always one of the goals of a deployment. In cases where integrity is not required, it does not make sense to employ TLS in the first place. There are attacks against confidentiality-only protection that utilize the lack of integrity to also break confidentiality (see, for instance, <span>[<a href="#DegabrieleP07" class="cite xref">DegabrieleP07</a>]</span> in the context of IPsec).<a href="#section-5.1-6" class="pilcrow">¶</a></p>
<p id="section-5.1-7">This document addresses itself to application protocols that are most commonly used on the Internet with TLS and DTLS. Typically, all communication between TLS clients and TLS servers requires all three of the above security services. This is particularly true where TLS clients are user agents like web browsers or email clients.<a href="#section-5.1-7" class="pilcrow">¶</a></p>
<p id="section-5.1-8">This document does not address the rarer deployment scenarios where one of the above three properties is not desired, such as the use case described in <a href="#oppsec" class="auto internal xref">Section 5.2</a>.  As another scenario where confidentiality is not needed, consider a monitored network where the authorities in charge of the respective traffic domain require full access to unencrypted (plaintext) traffic and where users collaborate and send their traffic in the clear.<a href="#section-5.1-8" class="pilcrow">¶</a></p>
</section>
</div>
<div id="oppsec">
<section id="section-5.2">
        <h3 id="name-opportunistic-security">
<a href="#section-5.2" class="section-number selfRef">5.2. </a><a href="#name-opportunistic-security" class="section-name selfRef">Opportunistic Security</a>
        </h3>
<p id="section-5.2-1">There are several important scenarios in which the use of TLS is optional, i.e., the client decides dynamically ("opportunistically") whether to use TLS with a particular server or to connect in the clear.  This practice, often called "opportunistic security", is described at length in <span>[<a href="#RFC7435" class="cite xref">RFC7435</a>]</span> and is often motivated by a desire for backward compatibility with legacy deployments.<a href="#section-5.2-1" class="pilcrow">¶</a></p>
<p id="section-5.2-2">In these scenarios, some of the recommendations in this document might be too strict, since adhering to them could cause fallback to cleartext, a worse outcome than using TLS with an outdated protocol version or cipher suite.<a href="#section-5.2-2" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="iana-considerations">
<section id="section-6">
      <h2 id="name-iana-considerations">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<p id="section-6-1">This document has no IANA actions.<a href="#section-6-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="sec">
<section id="section-7">
      <h2 id="name-security-considerations">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<p id="section-7-1">This entire document discusses the security practices directly affecting applications
    using the TLS protocol. This section contains broader security considerations related
    to technologies used in conjunction with or by TLS.
    The reader is referred to the Security Considerations sections of TLS 1.3
    <span>[<a href="#RFC8446" class="cite xref">RFC8446</a>]</span>, DTLS 1.3 <span>[<a href="#RFC9147" class="cite xref">RFC9147</a>]</span>, TLS 1.2 <span>[<a href="#RFC5246" class="cite xref">RFC5246</a>]</span>, and DTLS 1.2 <span>[<a href="#RFC6347" class="cite xref">RFC6347</a>]</span>
    for further context.<a href="#section-7-1" class="pilcrow">¶</a></p>
<div id="host-name-validation">
<section id="section-7.1">
        <h3 id="name-host-name-validation">
<a href="#section-7.1" class="section-number selfRef">7.1. </a><a href="#name-host-name-validation" class="section-name selfRef">Host Name Validation</a>
        </h3>
<p id="section-7.1-1">Application authors should take note that some TLS implementations
  do not validate host names.  If the TLS implementation they are
  using does not validate host names, authors might need to write their
  own validation code or consider using a different TLS implementation.<a href="#section-7.1-1" class="pilcrow">¶</a></p>
<p id="section-7.1-2">It is noted that the requirements regarding host name validation (and, in general, binding between the TLS layer and the protocol that runs above it) vary between different protocols. For HTTPS, these requirements are defined by Sections



  <a href="https://www.rfc-editor.org/rfc/rfc9110#section-4.3.3" class="relref">4.3.3</a>, <a href="https://www.rfc-editor.org/rfc/rfc9110#section-4.3.4" class="relref">4.3.4</a>, and <a href="https://www.rfc-editor.org/rfc/rfc9110#section-4.3.5" class="relref">4.3.5</a> of <span>[<a href="#RFC9110" class="cite xref">RFC9110</a>]</span>.<a href="#section-7.1-2" class="pilcrow">¶</a></p>
<p id="section-7.1-3">Host name validation is security-critical for all common TLS use cases. Without it, TLS ensures that the certificate is valid and guarantees possession of the private key but does not ensure that the connection terminates at the desired endpoint. Readers are referred to <span>[<a href="#RFC6125" class="cite xref">RFC6125</a>]</span> for further details regarding generic host name validation in the TLS context. In addition, that RFC contains a long list of application protocols, some of which implement a policy very different from HTTPS.<a href="#section-7.1-3" class="pilcrow">¶</a></p>
<p id="section-7.1-4">If the host name is discovered indirectly and insecurely (e.g., by a cleartext DNS query for an SRV or Mail Exchange (MX) record), it <span class="bcp14">SHOULD NOT</span> be used as a reference identifier <span>[<a href="#RFC6125" class="cite xref">RFC6125</a>]</span> even when it matches the presented certificate.  This proviso does not apply if the host name is discovered securely (for further discussion, see <span>[<a href="#RFC7673" class="cite xref">RFC7673</a>]</span> and <span>[<a href="#RFC7672" class="cite xref">RFC7672</a>]</span>).<a href="#section-7.1-4" class="pilcrow">¶</a></p>
<p id="section-7.1-5">Host name validation typically applies only to the leaf "end entity" certificate. Naturally, in order to ensure proper authentication in the context of the PKI, application clients need to verify the entire certification path in accordance with <span>[<a href="#RFC5280" class="cite xref">RFC5280</a>]</span>.<a href="#section-7.1-5" class="pilcrow">¶</a></p>
</section>
</div>
<div id="sec-aes">
<section id="section-7.2">
        <h3 id="name-aes-gcm">
<a href="#section-7.2" class="section-number selfRef">7.2. </a><a href="#name-aes-gcm" class="section-name selfRef">AES-GCM</a>
        </h3>
<p id="section-7.2-1"><a href="#rec-cipher" class="auto internal xref">Section 4.2</a> recommends the use of the AES-GCM authenticated encryption algorithm. Please refer to <span><a href="https://www.rfc-editor.org/rfc/rfc5288#section-6" class="relref">Section 6</a> of [<a href="#RFC5288" class="cite xref">RFC5288</a>]</span> for security considerations that apply specifically to AES-GCM when used with TLS.<a href="#section-7.2-1" class="pilcrow">¶</a></p>
<div id="nonce-reuse">
<section id="section-7.2.1">
          <h4 id="name-nonce-reuse-in-tls-12">
<a href="#section-7.2.1" class="section-number selfRef">7.2.1. </a><a href="#name-nonce-reuse-in-tls-12" class="section-name selfRef">Nonce Reuse in TLS 1.2</a>
          </h4>
<p id="section-7.2.1-1">The existence of deployed TLS stacks that mistakenly reuse the AES-GCM nonce is
documented in <span>[<a href="#Boeck2016" class="cite xref">Boeck2016</a>]</span>, showing there is an actual risk of AES-GCM getting
implemented insecurely and thus making TLS sessions that use an
AES-GCM cipher suite vulnerable to attacks such as <span>[<a href="#Joux2006" class="cite xref">Joux2006</a>]</span>.  (See <span>[<a href="#CVE" class="cite xref">CVE</a>]</span>
records: CVE-2016-0270, CVE-2016-10213, CVE-2016-10212, and CVE-2017-5933.)<a href="#section-7.2.1-1" class="pilcrow">¶</a></p>
<p id="section-7.2.1-2">While this problem has been fixed in TLS 1.3, which enforces a deterministic
method to generate nonces from record sequence numbers and shared secrets for
all its AEAD cipher suites (including AES-GCM), TLS 1.2 implementations
could still choose their own (potentially insecure) nonce generation methods.<a href="#section-7.2.1-2" class="pilcrow">¶</a></p>
<p id="section-7.2.1-3">It is therefore <span class="bcp14">RECOMMENDED</span> that TLS 1.2 implementations use the 64-bit
sequence number to populate the <code>nonce_explicit</code> part of the GCM nonce, as
described in the first two paragraphs of <span><a href="https://www.rfc-editor.org/rfc/rfc8446#section-5.3" class="relref">Section 5.3</a> of [<a href="#RFC8446" class="cite xref">RFC8446</a>]</span>. This stronger recommendation updates <span><a href="https://www.rfc-editor.org/rfc/rfc5288#section-3" class="relref">Section 3</a> of [<a href="#RFC5288" class="cite xref">RFC5288</a>]</span>, which specifies that the use of 64-bit sequence numbers to populate the <code>nonce_explicit</code> field is optional.<a href="#section-7.2.1-3" class="pilcrow">¶</a></p>
<p id="section-7.2.1-4">We note that at the time of writing, there are no cipher suites defined for nonce-reuse-resistant algorithms such as AES-GCM-SIV <span>[<a href="#RFC8452" class="cite xref">RFC8452</a>]</span>.<a href="#section-7.2.1-4" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="sec-pfs">
<section id="section-7.3">
        <h3 id="name-forward-secrecy">
<a href="#section-7.3" class="section-number selfRef">7.3. </a><a href="#name-forward-secrecy" class="section-name selfRef">Forward Secrecy</a>
        </h3>
<p id="section-7.3-1">Forward secrecy (also called "perfect forward secrecy" or "PFS" and defined in <span>[<a href="#RFC4949" class="cite xref">RFC4949</a>]</span>) is a defense against an attacker who records encrypted conversations where the session keys are only encrypted with the communicating parties' long-term keys.<a href="#section-7.3-1" class="pilcrow">¶</a></p>
<p id="section-7.3-2">Should the attacker be able to obtain these long-term keys at some point later in time, the session keys and thus the entire conversation could be decrypted.<a href="#section-7.3-2" class="pilcrow">¶</a></p>
<p id="section-7.3-3">In the context of TLS and DTLS, such compromise of long-term keys is not entirely implausible. It can happen, for example, due to:<a href="#section-7.3-3" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-7.3-4.1">A client or server being attacked by some other attack vector, and the private key retrieved.<a href="#section-7.3-4.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.3-4.2">A long-term key retrieved from a device that has been sold or otherwise decommissioned without prior wiping.<a href="#section-7.3-4.2" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.3-4.3">A long-term key used on a device as a default key <span>[<a href="#Heninger2012" class="cite xref">Heninger2012</a>]</span>.<a href="#section-7.3-4.3" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.3-4.4">A key generated by a trusted third party like a CA and later retrieved from it by either extortion or compromise <span>[<a href="#Soghoian2011" class="cite xref">Soghoian2011</a>]</span>.<a href="#section-7.3-4.4" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.3-4.5">A cryptographic breakthrough or the use of asymmetric keys with insufficient length <span>[<a href="#Kleinjung2010" class="cite xref">Kleinjung2010</a>]</span>.<a href="#section-7.3-4.5" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.3-4.6">Social engineering attacks against system administrators.<a href="#section-7.3-4.6" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.3-4.7">Collection of private keys from inadequately protected backups.<a href="#section-7.3-4.7" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-7.3-5">Forward secrecy ensures in such cases that it is not feasible for an attacker to determine the session keys even if the attacker has obtained the long-term keys some time after the conversation. It also protects against an attacker who is in possession of the long-term keys but remains passive during the conversation.<a href="#section-7.3-5" class="pilcrow">¶</a></p>
<p id="section-7.3-6">Forward secrecy is generally achieved by using the Diffie-Hellman scheme to derive session keys. The Diffie-Hellman scheme has both parties maintain private secrets and send parameters over the network as modular powers over certain cyclic groups. The properties of the so-called Discrete Logarithm Problem (DLP) allow the parties to derive the session keys without an eavesdropper being able to do so. There is currently no known attack against DLP if sufficiently large parameters are chosen. A variant of the Diffie-Hellman scheme uses elliptic curves instead of the originally proposed modular arithmetic. Given the current state of the art, Elliptic Curve Diffie-Hellman appears to be more efficient, permits shorter key lengths, and allows less freedom for implementation errors than finite-field Diffie-Hellman.<a href="#section-7.3-6" class="pilcrow">¶</a></p>
<p id="section-7.3-7">Unfortunately, many TLS/DTLS cipher suites were defined that do not feature forward secrecy, e.g., TLS_RSA_WITH_AES_256_CBC_SHA256.  This document therefore advocates strict use of forward-secrecy-only ciphers.<a href="#section-7.3-7" class="pilcrow">¶</a></p>
</section>
</div>
<div id="sec-dhe">
<section id="section-7.4">
        <h3 id="name-diffie-hellman-exponent-reu">
<a href="#section-7.4" class="section-number selfRef">7.4. </a><a href="#name-diffie-hellman-exponent-reu" class="section-name selfRef">Diffie-Hellman Exponent Reuse</a>
        </h3>
<p id="section-7.4-1">For performance reasons, it is not uncommon for TLS implementations to reuse Diffie-Hellman and Elliptic Curve Diffie-Hellman exponents across multiple connections. Such reuse can result in major security issues:<a href="#section-7.4-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-7.4-2.1">If exponents are reused for too long (in some cases, even as little as a few hours), an attacker who gains access to the host can decrypt previous connections. In other words, exponent reuse negates the effects of forward secrecy.<a href="#section-7.4-2.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.4-2.2">TLS implementations that reuse exponents should test the DH public key they receive for group membership, in order to avoid some known attacks. These tests are not standardized in TLS at the time of writing, although general guidance in this area is provided by <span>[<a href="#NIST.SP.800-56A" class="cite xref">NIST.SP.800-56A</a>]</span> and available in many protocol implementations.<a href="#section-7.4-2.2" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.4-2.3">Under certain conditions, the use of static finite-field DH keys, or of ephemeral finite-field DH keys that are reused across multiple connections, can lead to timing attacks (such as those described in <span>[<a href="#RACCOON" class="cite xref">RACCOON</a>]</span>) on the shared secrets used in Diffie-Hellman key exchange.<a href="#section-7.4-2.3" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.4-2.4">An "invalid curve" attack can be mounted against Elliptic Curve DH if the victim does not verify that the received point lies on the correct curve.  If the victim is reusing the DH secrets, the attacker can repeat the probe varying the points to recover the full secret (see <span>[<a href="#Antipa2003" class="cite xref">Antipa2003</a>]</span> and <span>[<a href="#Jager2015" class="cite xref">Jager2015</a>]</span>).<a href="#section-7.4-2.4" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-7.4-3">To address these concerns:<a href="#section-7.4-3" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-7.4-4.1">TLS implementations <span class="bcp14">SHOULD NOT</span> use static finite-field DH keys and <span class="bcp14">SHOULD NOT</span> reuse ephemeral finite-field DH keys across multiple connections.<a href="#section-7.4-4.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.4-4.2">Server implementations that want to reuse Elliptic Curve DH keys <span class="bcp14">SHOULD</span> either use a "safe curve" <span>[<a href="#SAFECURVES" class="cite xref">SAFECURVES</a>]</span> (e.g., X25519) or perform the checks described in <span>[<a href="#NIST.SP.800-56A" class="cite xref">NIST.SP.800-56A</a>]</span> on the received points.<a href="#section-7.4-4.2" class="pilcrow">¶</a>
</li>
        </ul>
</section>
</div>
<div id="certificate-revocation">
<section id="section-7.5">
        <h3 id="name-certificate-revocation">
<a href="#section-7.5" class="section-number selfRef">7.5. </a><a href="#name-certificate-revocation" class="section-name selfRef">Certificate Revocation</a>
        </h3>
<p id="section-7.5-1">The following considerations and recommendations represent the current state of the art regarding certificate revocation, even though no complete and efficient solution exists for the problem of checking the revocation status of common public key certificates <span>[<a href="#RFC5280" class="cite xref">RFC5280</a>]</span>:<a href="#section-7.5-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-7.5-2.1">Certificate revocation is an important tool when recovering from attacks on the TLS implementation as well as cases of misissued certificates. TLS implementations <span class="bcp14">MUST</span> implement a strategy to distrust revoked certificates.<a href="#section-7.5-2.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.5-2.2">Although Certificate Revocation Lists (CRLs) are the most widely supported mechanism for distributing revocation information, they have known scaling challenges that limit their usefulness, despite workarounds such as partitioned CRLs and delta CRLs. The more modern <span>[<a href="#CRLite" class="cite xref">CRLite</a>]</span> and the follow-on Let's Revoke <span>[<a href="#LetsRevoke" class="cite xref">LetsRevoke</a>]</span> build on the availability of Certificate Transparency <span>[<a href="#RFC9162" class="cite xref">RFC9162</a>]</span> logs and aggressive compression to allow practical use of the CRL infrastructure, but at the time of writing, neither solution is deployed for client-side revocation processing at scale.<a href="#section-7.5-2.2" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.5-2.3">Proprietary mechanisms that embed revocation lists in the web browser's configuration database cannot scale beyond the few most heavily used web servers.<a href="#section-7.5-2.3" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.5-2.4">The Online Certification Status Protocol (OCSP) <span>[<a href="#RFC6960" class="cite xref">RFC6960</a>]</span> in its basic form presents both scaling and privacy issues. In addition, clients typically "soft-fail", meaning that they do not abort the TLS connection if the OCSP server does not respond. (However, this might be a workaround to avoid denial-of-service attacks if an OCSP responder is taken offline.) For a recent survey of the status of OCSP deployment in the web PKI, see <span>[<a href="#Chung18" class="cite xref">Chung18</a>]</span>.<a href="#section-7.5-2.4" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.5-2.5">The TLS Certificate Status Request extension (<span><a href="https://www.rfc-editor.org/rfc/rfc6066#section-8" class="relref">Section 8</a> of [<a href="#RFC6066" class="cite xref">RFC6066</a>]</span>), commonly called "OCSP stapling", resolves the operational issues with OCSP. However, it is still ineffective in the presence of an active on-path attacker because the attacker can simply ignore the client's request for a stapled OCSP response.<a href="#section-7.5-2.5" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.5-2.6">
            <span>[<a href="#RFC7633" class="cite xref">RFC7633</a>]</span> defines a certificate extension that indicates that clients must expect stapled OCSP responses for the certificate and must abort the handshake ("hard-fail") if such a response is not available.<a href="#section-7.5-2.6" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.5-2.7">OCSP stapling as used in TLS 1.2 does not extend to intermediate certificates within a certificate chain. The Multiple Certificate Status extension <span>[<a href="#RFC6961" class="cite xref">RFC6961</a>]</span> addresses this shortcoming, but it has seen little deployment and had been deprecated by <span>[<a href="#RFC8446" class="cite xref">RFC8446</a>]</span>. As a result, although this extension was recommended for TLS 1.2 in <span>[<a href="#RFC7525" class="cite xref">RFC7525</a>]</span>, it is no longer recommended by this document.<a href="#section-7.5-2.7" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.5-2.8">TLS 1.3 (<span><a href="https://www.rfc-editor.org/rfc/rfc8446#section-4.4.2.1" class="relref">Section 4.4.2.1</a> of [<a href="#RFC8446" class="cite xref">RFC8446</a>]</span>) allows the association of OCSP information with intermediate certificates by using an extension to the CertificateEntry structure. However, using this facility remains impractical because many certification authorities (CAs) either do not publish OCSP for CA certificates or publish OCSP reports with a lifetime that is too long to be useful.<a href="#section-7.5-2.8" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-7.5-2.9">Both CRLs and OCSP depend on relatively reliable connectivity to the Internet, which might not be available to certain kinds of nodes. A common example is newly provisioned devices that need to establish a secure connection in order to boot up for the first time.<a href="#section-7.5-2.9" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-7.5-3">For the common use cases of public key certificates in TLS, servers <span class="bcp14">SHOULD</span> support the following as a best practice given the current state of the art and as a foundation for a possible future solution: OCSP <span>[<a href="#RFC6960" class="cite xref">RFC6960</a>]</span> and OCSP stapling using the <code>status_request</code> extension defined in <span>[<a href="#RFC6066" class="cite xref">RFC6066</a>]</span>. Note that the exact mechanism for embedding the <code>status_request</code> extension differs between TLS 1.2 and 1.3. As a matter of local policy, server operators <span class="bcp14">MAY</span> request that CAs issue must-staple <span>[<a href="#RFC7633" class="cite xref">RFC7633</a>]</span> certificates for the server and/or for client authentication, but we recommend reviewing the operational conditions before deciding on this approach.<a href="#section-7.5-3" class="pilcrow">¶</a></p>
<p id="section-7.5-4">The considerations in this section do not apply to scenarios where the DNS-Based
              Authentication of Named Entities (DANE) TLSA resource record <span>[<a href="#RFC6698" class="cite xref">RFC6698</a>]</span> is used to signal to a client which certificate a server considers valid and good to use for TLS connections.<a href="#section-7.5-4" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<section id="section-8">
      <h2 id="name-references">
<a href="#section-8" class="section-number selfRef">8. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-8.1">
        <h3 id="name-normative-references">
<a href="#section-8.1" class="section-number selfRef">8.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<dt id="RFC2119">[RFC2119]</dt>
        <dd>
<span class="refAuthor">Bradner, S.</span>, <span class="refTitle">"Key words for use in RFCs to Indicate Requirement Levels"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 2119</span>, <span class="seriesInfo">DOI 10.17487/RFC2119</span>, <time datetime="1997-03" class="refDate">March 1997</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2119">https://www.rfc-editor.org/info/rfc2119</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3766">[RFC3766]</dt>
        <dd>
<span class="refAuthor">Orman, H.</span> and <span class="refAuthor">P. Hoffman</span>, <span class="refTitle">"Determining Strengths For Public Keys Used For Exchanging Symmetric Keys"</span>, <span class="seriesInfo">BCP 86</span>, <span class="seriesInfo">RFC 3766</span>, <span class="seriesInfo">DOI 10.17487/RFC3766</span>, <time datetime="2004-04" class="refDate">April 2004</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3766">https://www.rfc-editor.org/info/rfc3766</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5246">[RFC5246]</dt>
        <dd>
<span class="refAuthor">Dierks, T.</span> and <span class="refAuthor">E. Rescorla</span>, <span class="refTitle">"The Transport Layer Security (TLS) Protocol Version 1.2"</span>, <span class="seriesInfo">RFC 5246</span>, <span class="seriesInfo">DOI 10.17487/RFC5246</span>, <time datetime="2008-08" class="refDate">August 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5246">https://www.rfc-editor.org/info/rfc5246</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5288">[RFC5288]</dt>
        <dd>
<span class="refAuthor">Salowey, J.</span>, <span class="refAuthor">Choudhury, A.</span>, and <span class="refAuthor">D. McGrew</span>, <span class="refTitle">"AES Galois Counter Mode (GCM) Cipher Suites for TLS"</span>, <span class="seriesInfo">RFC 5288</span>, <span class="seriesInfo">DOI 10.17487/RFC5288</span>, <time datetime="2008-08" class="refDate">August 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5288">https://www.rfc-editor.org/info/rfc5288</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5746">[RFC5746]</dt>
        <dd>
<span class="refAuthor">Rescorla, E.</span>, <span class="refAuthor">Ray, M.</span>, <span class="refAuthor">Dispensa, S.</span>, and <span class="refAuthor">N. Oskov</span>, <span class="refTitle">"Transport Layer Security (TLS) Renegotiation Indication Extension"</span>, <span class="seriesInfo">RFC 5746</span>, <span class="seriesInfo">DOI 10.17487/RFC5746</span>, <time datetime="2010-02" class="refDate">February 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5746">https://www.rfc-editor.org/info/rfc5746</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6066">[RFC6066]</dt>
        <dd>
<span class="refAuthor">Eastlake 3rd, D.</span>, <span class="refTitle">"Transport Layer Security (TLS) Extensions: Extension Definitions"</span>, <span class="seriesInfo">RFC 6066</span>, <span class="seriesInfo">DOI 10.17487/RFC6066</span>, <time datetime="2011-01" class="refDate">January 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6066">https://www.rfc-editor.org/info/rfc6066</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6125">[RFC6125]</dt>
        <dd>
<span class="refAuthor">Saint-Andre, P.</span> and <span class="refAuthor">J. Hodges</span>, <span class="refTitle">"Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)"</span>, <span class="seriesInfo">RFC 6125</span>, <span class="seriesInfo">DOI 10.17487/RFC6125</span>, <time datetime="2011-03" class="refDate">March 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6125">https://www.rfc-editor.org/info/rfc6125</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6176">[RFC6176]</dt>
        <dd>
<span class="refAuthor">Turner, S.</span> and <span class="refAuthor">T. Polk</span>, <span class="refTitle">"Prohibiting Secure Sockets Layer (SSL) Version 2.0"</span>, <span class="seriesInfo">RFC 6176</span>, <span class="seriesInfo">DOI 10.17487/RFC6176</span>, <time datetime="2011-03" class="refDate">March 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6176">https://www.rfc-editor.org/info/rfc6176</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6347">[RFC6347]</dt>
        <dd>
<span class="refAuthor">Rescorla, E.</span> and <span class="refAuthor">N. Modadugu</span>, <span class="refTitle">"Datagram Transport Layer Security Version 1.2"</span>, <span class="seriesInfo">RFC 6347</span>, <span class="seriesInfo">DOI 10.17487/RFC6347</span>, <time datetime="2012-01" class="refDate">January 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6347">https://www.rfc-editor.org/info/rfc6347</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6979">[RFC6979]</dt>
        <dd>
<span class="refAuthor">Pornin, T.</span>, <span class="refTitle">"Deterministic Usage of the Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA)"</span>, <span class="seriesInfo">RFC 6979</span>, <span class="seriesInfo">DOI 10.17487/RFC6979</span>, <time datetime="2013-08" class="refDate">August 2013</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6979">https://www.rfc-editor.org/info/rfc6979</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7301">[RFC7301]</dt>
        <dd>
<span class="refAuthor">Friedl, S.</span>, <span class="refAuthor">Popov, A.</span>, <span class="refAuthor">Langley, A.</span>, and <span class="refAuthor">E. Stephan</span>, <span class="refTitle">"Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension"</span>, <span class="seriesInfo">RFC 7301</span>, <span class="seriesInfo">DOI 10.17487/RFC7301</span>, <time datetime="2014-07" class="refDate">July 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7301">https://www.rfc-editor.org/info/rfc7301</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7366">[RFC7366]</dt>
        <dd>
<span class="refAuthor">Gutmann, P.</span>, <span class="refTitle">"Encrypt-then-MAC for Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)"</span>, <span class="seriesInfo">RFC 7366</span>, <span class="seriesInfo">DOI 10.17487/RFC7366</span>, <time datetime="2014-09" class="refDate">September 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7366">https://www.rfc-editor.org/info/rfc7366</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7465">[RFC7465]</dt>
        <dd>
<span class="refAuthor">Popov, A.</span>, <span class="refTitle">"Prohibiting RC4 Cipher Suites"</span>, <span class="seriesInfo">RFC 7465</span>, <span class="seriesInfo">DOI 10.17487/RFC7465</span>, <time datetime="2015-02" class="refDate">February 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7465">https://www.rfc-editor.org/info/rfc7465</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7627">[RFC7627]</dt>
        <dd>
<span class="refAuthor">Bhargavan, K., Ed.</span>, <span class="refAuthor">Delignat-Lavaud, A.</span>, <span class="refAuthor">Pironti, A.</span>, <span class="refAuthor">Langley, A.</span>, and <span class="refAuthor">M. Ray</span>, <span class="refTitle">"Transport Layer Security (TLS) Session Hash and Extended Master Secret Extension"</span>, <span class="seriesInfo">RFC 7627</span>, <span class="seriesInfo">DOI 10.17487/RFC7627</span>, <time datetime="2015-09" class="refDate">September 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7627">https://www.rfc-editor.org/info/rfc7627</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7748">[RFC7748]</dt>
        <dd>
<span class="refAuthor">Langley, A.</span>, <span class="refAuthor">Hamburg, M.</span>, and <span class="refAuthor">S. Turner</span>, <span class="refTitle">"Elliptic Curves for Security"</span>, <span class="seriesInfo">RFC 7748</span>, <span class="seriesInfo">DOI 10.17487/RFC7748</span>, <time datetime="2016-01" class="refDate">January 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7748">https://www.rfc-editor.org/info/rfc7748</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8174">[RFC8174]</dt>
        <dd>
<span class="refAuthor">Leiba, B.</span>, <span class="refTitle">"Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 8174</span>, <span class="seriesInfo">DOI 10.17487/RFC8174</span>, <time datetime="2017-05" class="refDate">May 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8174">https://www.rfc-editor.org/info/rfc8174</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8422">[RFC8422]</dt>
        <dd>
<span class="refAuthor">Nir, Y.</span>, <span class="refAuthor">Josefsson, S.</span>, and <span class="refAuthor">M. Pegourie-Gonnard</span>, <span class="refTitle">"Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS) Versions 1.2 and Earlier"</span>, <span class="seriesInfo">RFC 8422</span>, <span class="seriesInfo">DOI 10.17487/RFC8422</span>, <time datetime="2018-08" class="refDate">August 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8422">https://www.rfc-editor.org/info/rfc8422</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8446">[RFC8446]</dt>
        <dd>
<span class="refAuthor">Rescorla, E.</span>, <span class="refTitle">"The Transport Layer Security (TLS) Protocol Version 1.3"</span>, <span class="seriesInfo">RFC 8446</span>, <span class="seriesInfo">DOI 10.17487/RFC8446</span>, <time datetime="2018-08" class="refDate">August 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8446">https://www.rfc-editor.org/info/rfc8446</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8996">[RFC8996]</dt>
        <dd>
<span class="refAuthor">Moriarty, K.</span> and <span class="refAuthor">S. Farrell</span>, <span class="refTitle">"Deprecating TLS 1.0 and TLS 1.1"</span>, <span class="seriesInfo">BCP 195</span>, <span class="seriesInfo">RFC 8996</span>, <span class="seriesInfo">DOI 10.17487/RFC8996</span>, <time datetime="2021-03" class="refDate">March 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8996">https://www.rfc-editor.org/info/rfc8996</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9147">[RFC9147]</dt>
        <dd>
<span class="refAuthor">Rescorla, E.</span>, <span class="refAuthor">Tschofenig, H.</span>, and <span class="refAuthor">N. Modadugu</span>, <span class="refTitle">"The Datagram Transport Layer Security (DTLS) Protocol Version 1.3"</span>, <span class="seriesInfo">RFC 9147</span>, <span class="seriesInfo">DOI 10.17487/RFC9147</span>, <time datetime="2022-04" class="refDate">April 2022</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc9147">https://www.rfc-editor.org/info/rfc9147</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9155">[RFC9155]</dt>
      <dd>
<span class="refAuthor">Velvindron, L.</span>, <span class="refAuthor">Moriarty, K.</span>, and <span class="refAuthor">A. Ghedini</span>, <span class="refTitle">"Deprecating MD5 and SHA-1 Signature Hashes in TLS 1.2 and DTLS 1.2"</span>, <span class="seriesInfo">RFC 9155</span>, <span class="seriesInfo">DOI 10.17487/RFC9155</span>, <time datetime="2021-12" class="refDate">December 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc9155">https://www.rfc-editor.org/info/rfc9155</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
<section id="section-8.2">
        <h3 id="name-informative-references">
<a href="#section-8.2" class="section-number selfRef">8.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="I-D.irtf-cfrg-aead-limits">[AEAD-LIMITS]</dt>
        <dd>
<span class="refAuthor">Günther, F.</span>, <span class="refAuthor">Thomson, M.</span>, and <span class="refAuthor">C. A. Wood</span>, <span class="refTitle">"Usage Limits on AEAD Algorithms"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-irtf-cfrg-aead-limits-05</span>, <time datetime="2022-07-11" class="refDate">11 July 2022</time>, <span>&lt;<a href="https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-aead-limits-05">https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-aead-limits-05</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="ALPACA">[ALPACA]</dt>
        <dd>
<span class="refAuthor">Brinkmann, M.</span>, <span class="refAuthor">Dresen, C.</span>, <span class="refAuthor">Merget, R.</span>, <span class="refAuthor">Poddebniak, D.</span>, <span class="refAuthor">Müller, J.</span>, <span class="refAuthor">Somorovsky, J.</span>, <span class="refAuthor">Schwenk, J.</span>, and <span class="refAuthor">S. Schinzel</span>, <span class="refTitle">"ALPACA: Application Layer Protocol Confusion - Analyzing and Mitigating Cracks in TLS Authentication"</span>, <span class="refContent">30th USENIX Security Symposium (USENIX Security 21)</span>, <time datetime="2021-08" class="refDate">August 2021</time>, <span>&lt;<a href="https://www.usenix.org/conference/usenixsecurity21/presentation/brinkmann">https://www.usenix.org/conference/usenixsecurity21/presentation/brinkmann</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Antipa2003">[Antipa2003]</dt>
        <dd>
<span class="refAuthor">Antipa, A.</span>, <span class="refAuthor">Brown, D. R. L.</span>, <span class="refAuthor">Menezes, A.</span>, <span class="refAuthor">Struik, R.</span>, and <span class="refAuthor">S. Vanstone</span>, <span class="refTitle">"Validation of Elliptic Curve Public Keys"</span>, <span class="refContent">Public Key Cryptography - PKC 2003</span>, <time datetime="2003-12" class="refDate">December 2003</time>, <span>&lt;<a href="https://doi.org/10.1007/3-540-36288-6_16">https://doi.org/10.1007/3-540-36288-6_16</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Boeck2016">[Boeck2016]</dt>
        <dd>
<span class="refAuthor">Böck, H.</span>, <span class="refAuthor">Zauner, A.</span>, <span class="refAuthor">Devlin, S.</span>, <span class="refAuthor">Somorovsky, J.</span>, and <span class="refAuthor">P. Jovanovic</span>, <span class="refTitle">"Nonce-Disrespecting Adversaries: Practical Forgery Attacks on GCM in TLS"</span>, <time datetime="2016-05" class="refDate">May 2016</time>, <span>&lt;<a href="https://eprint.iacr.org/2016/475.pdf">https://eprint.iacr.org/2016/475.pdf</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="CAB-Baseline">[CAB-Baseline]</dt>
        <dd>
<span class="refAuthor">CA/Browser Forum</span>, <span class="refTitle">"Baseline Requirements for the Issuance and Management of Publicly-Trusted Certificates"</span>, <span class="seriesInfo">Version 1.8.4</span>, <time datetime="2022-04" class="refDate">April 2022</time>, <span>&lt;<a href="https://cabforum.org/documents/">https://cabforum.org/documents/</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="I-D.mattsson-cfrg-det-sigs-with-noise">[CFRG-DET-SIGS]</dt>
        <dd>
<span class="refAuthor">Preuß Mattsson, J.</span>, <span class="refAuthor">Thormarker, E.</span>, and <span class="refAuthor">S. Ruohomaa</span>, <span class="refTitle">"Deterministic ECDSA and EdDSA Signatures with Additional Randomness"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-irtf-cfrg-det-sigs-with-noise-00</span>, <time datetime="2022-08-08" class="refDate">8 August 2022</time>, <span>&lt;<a href="https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-det-sigs-with-noise-00">https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-det-sigs-with-noise-00</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Chung18">[Chung18]</dt>
        <dd>
<span class="refAuthor">Chung, T.</span>, <span class="refAuthor">Lok, J.</span>, <span class="refAuthor">Chandrasekaran, B.</span>, <span class="refAuthor">Choffnes, D.</span>, <span class="refAuthor">Levin, D.</span>, <span class="refAuthor">Maggs, B.</span>, <span class="refAuthor">Mislove, A.</span>, <span class="refAuthor">Rula, J.</span>, <span class="refAuthor">Sullivan, N.</span>, and <span class="refAuthor">C. Wilson</span>, <span class="refTitle">"Is the Web Ready for OCSP Must-Staple?"</span>, <span class="refContent">Proceedings of the Internet Measurement Conference 2018</span>, <span class="seriesInfo">DOI 10.1145/3278532.3278543</span>, <time datetime="2018-10" class="refDate">October 2018</time>, <span>&lt;<a href="https://doi.org/10.1145/3278532.3278543">https://doi.org/10.1145/3278532.3278543</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="CRLite">[CRLite]</dt>
        <dd>
<span class="refAuthor">Larisch, J.</span>, <span class="refAuthor">Choffnes, D.</span>, <span class="refAuthor">Levin, D.</span>, <span class="refAuthor">Maggs, B.</span>, <span class="refAuthor">Mislove, A.</span>, and <span class="refAuthor">C. Wilson</span>, <span class="refTitle">"CRLite: A Scalable System for Pushing All TLS Revocations to All Browsers"</span>, <span class="refContent">2017 IEEE Symposium on Security and Privacy (SP)</span>, <span class="seriesInfo">DOI 10.1109/sp.2017.17</span>, <time datetime="2017-05" class="refDate">May 2017</time>, <span>&lt;<a href="https://doi.org/10.1109/sp.2017.17">https://doi.org/10.1109/sp.2017.17</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="CVE">[CVE]</dt>
        <dd>
<span class="refAuthor">MITRE</span>, <span class="refTitle">"Common Vulnerabilities and Exposures"</span>, <span>&lt;<a href="https://cve.mitre.org">https://cve.mitre.org</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="DegabrieleP07">[DegabrieleP07]</dt>
        <dd>
<span class="refAuthor">Degabriele, J.</span> and <span class="refAuthor">K. Paterson</span>, <span class="refTitle">"Attacking the IPsec Standards in Encryption-only Configurations"</span>, <span class="refContent">2007 IEEE Symposium on Security and Privacy (SP '07)</span>, <span class="seriesInfo">DOI 10.1109/sp.2007.8</span>, <time datetime="2007-05" class="refDate">May 2007</time>, <span>&lt;<a href="https://doi.org/10.1109/sp.2007.8">https://doi.org/10.1109/sp.2007.8</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="DROWN">[DROWN]</dt>
        <dd>
<span class="refAuthor">Aviram, N.</span>, <span class="refAuthor">Schinzel, S.</span>, <span class="refAuthor">Somorovsky, J.</span>, <span class="refAuthor">Heninger, N.</span>, <span class="refAuthor">Dankel, M.</span>, <span class="refAuthor">Steube, J.</span>, <span class="refAuthor">Valenta, L.</span>, <span class="refAuthor">Adrian, D.</span>, <span class="refAuthor">Halderman, J.</span>, <span class="refAuthor">Dukhovni, V.</span>, <span class="refAuthor">Käsper, E.</span>, <span class="refAuthor">Cohney, S.</span>, <span class="refAuthor">Engels, S.</span>, <span class="refAuthor">Paar, C.</span>, and <span class="refAuthor">Y. Shavitt</span>, <span class="refTitle">"DROWN: Breaking TLS using SSLv2"</span>, <span class="refContent">25th USENIX Security Symposium (USENIX Security 16)</span>, <time datetime="2016-08" class="refDate">August 2016</time>, <span>&lt;<a href="https://www.usenix.org/conference/usenixsecurity16/technical-sessions/presentation/aviram">https://www.usenix.org/conference/usenixsecurity16/technical-sessions/presentation/aviram</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Heninger2012">[Heninger2012]</dt>
        <dd>
<span class="refAuthor">Heninger, N.</span>, <span class="refAuthor">Durumeric, Z.</span>, <span class="refAuthor">Wustrow, E.</span>, and <span class="refAuthor">J. A. Halderman</span>, <span class="refTitle">"Mining Your Ps and Qs: Detection of Widespread Weak Keys in Network Devices"</span>, <span class="refContent">21st Usenix Security Symposium</span>, <time datetime="2012-08" class="refDate">August 2012</time>. </dd>
<dd class="break"></dd>
<dt id="IANA_TLS">[IANA_TLS]</dt>
        <dd>
<span class="refAuthor">IANA</span>, <span class="refTitle">"Transport Layer Security (TLS) Parameters"</span>, <span>&lt;<a href="https://www.iana.org/assignments/tls-parameters">https://www.iana.org/assignments/tls-parameters</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="I-D.ietf-uta-tls13-iot-profile">[IOT-PROFILE]</dt>
        <dd>
<span class="refAuthor">Tschofenig, H.</span> and <span class="refAuthor">T. Fossati</span>, <span class="refTitle">"TLS/DTLS 1.3 Profiles for the Internet of Things"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-ietf-uta-tls13-iot-profile-05</span>, <time datetime="2022-07-06" class="refDate">6 July 2022</time>, <span>&lt;<a href="https://datatracker.ietf.org/doc/html/draft-ietf-uta-tls13-iot-profile-05">https://datatracker.ietf.org/doc/html/draft-ietf-uta-tls13-iot-profile-05</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Jager2015">[Jager2015]</dt>
        <dd>
<span class="refAuthor">Jager, T.</span>, <span class="refAuthor">Schwenk, J.</span>, and <span class="refAuthor">J. Somorovsky</span>, <span class="refTitle">"Practical Invalid Curve Attacks on TLS-ECDH"</span>, <span class="refContent">Computer Security -- ESORICS 2015, pp. 407-425</span>, <span class="seriesInfo">DOI 10.1007/978-3-319-24174-6_21</span>, <time datetime="2015" class="refDate">2015</time>, <span>&lt;<a href="https://doi.org/10.1007/978-3-319-24174-6_21">https://doi.org/10.1007/978-3-319-24174-6_21</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Joux2006">[Joux2006]</dt>
        <dd>
<span class="refAuthor">Joux, A.</span>, <span class="refTitle">"Authentication Failures in NIST version of GCM"</span>, <time datetime="2006" class="refDate">2006</time>, <span>&lt;<a href="https://csrc.nist.gov/csrc/media/projects/block-cipher-techniques/documents/bcm/comments/800-38-series-drafts/gcm/joux_comments.pdf">https://csrc.nist.gov/csrc/media/projects/block-cipher-techniques/documents/bcm/comments/800-38-series-drafts/gcm/joux_comments.pdf</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Kim2014">[Kim2014]</dt>
        <dd>
<span class="refAuthor">Kim, Y.</span>, <span class="refAuthor">Daly, R.</span>, <span class="refAuthor">Kim, J.</span>, <span class="refAuthor">Fallin, C.</span>, <span class="refAuthor">Lee, J. H.</span>, <span class="refAuthor">Lee, D.</span>, <span class="refAuthor">Wilkerson, C.</span>, <span class="refAuthor">Lai, K.</span>, and <span class="refAuthor">O. Mutlu</span>, <span class="refTitle">"Flipping Bits in Memory Without Accessing Them: An Experimental Study of DRAM Disturbance Errors"</span>, <span class="seriesInfo">DOI 10.1109/ISCA.2014.6853210</span>, <time datetime="2014-07" class="refDate">July 2014</time>, <span>&lt;<a href="https://users.ece.cmu.edu/~yoonguk/papers/kim-isca14.pdf">https://users.ece.cmu.edu/~yoonguk/papers/kim-isca14.pdf</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Kleinjung2010">[Kleinjung2010]</dt>
        <dd>
<span class="refAuthor">Kleinjung, T.</span>, <span class="refAuthor">Aoki, K.</span>, <span class="refAuthor">Franke, J.</span>, <span class="refAuthor">Lenstra, A.</span>, <span class="refAuthor">Thomé, E.</span>, <span class="refAuthor">Bos, J.</span>, <span class="refAuthor">Gaudry, P.</span>, <span class="refAuthor">Kruppa, A.</span>, <span class="refAuthor">Montgomery, P.</span>, <span class="refAuthor">Osvik, D.</span>, <span class="refAuthor">te Riele, H.</span>, <span class="refAuthor">Timofeev, A.</span>, and <span class="refAuthor">P. Zimmermann</span>, <span class="refTitle">"Factorization of a 768-Bit RSA Modulus"</span>, <span class="refContent">Advances in Cryptology - CRYPTO 2010, pp. 333-350</span>, <span class="seriesInfo">DOI 10.1007/978-3-642-14623-7_18</span>, <time datetime="2010" class="refDate">2010</time>, <span>&lt;<a href="https://doi.org/10.1007/978-3-642-14623-7_18">https://doi.org/10.1007/978-3-642-14623-7_18</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="LetsRevoke">[LetsRevoke]</dt>
        <dd>
<span class="refAuthor">Smith, T.</span>, <span class="refAuthor">Dickinson, L.</span>, and <span class="refAuthor">K. Seamons</span>, <span class="refTitle">"Let's Revoke: Scalable Global Certificate Revocation"</span>, <span class="refContent">Proceedings 2020 Network and Distributed System Security Symposium</span>, <span class="seriesInfo">DOI 10.14722/ndss.2020.24084</span>, <time datetime="2020-02" class="refDate">February 2020</time>, <span>&lt;<a href="https://doi.org/10.14722/ndss.2020.24084">https://doi.org/10.14722/ndss.2020.24084</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Logjam">[Logjam]</dt>
        <dd>
<span class="refAuthor">Adrian, D.</span>, <span class="refAuthor">Bhargavan, K.</span>, <span class="refAuthor">Durumeric, Z.</span>, <span class="refAuthor">Gaudry, P.</span>, <span class="refAuthor">Green, M.</span>, <span class="refAuthor">Halderman, J.</span>, <span class="refAuthor">Heninger, N.</span>, <span class="refAuthor">Springall, D.</span>, <span class="refAuthor">Thomé, E.</span>, <span class="refAuthor">Valenta, L.</span>, <span class="refAuthor">VanderSloot, B.</span>, <span class="refAuthor">Wustrow, E.</span>, <span class="refAuthor">Zanella-Béguelin, S.</span>, and <span class="refAuthor">P. Zimmermann</span>, <span class="refTitle">"Imperfect Forward Secrecy: How Diffie-Hellman Fails in Practice"</span>, <span class="refContent">Proceedings of the 22nd ACM SIGSAC Conference on Computer and Communications Security, pp. 5-17</span>, <span class="seriesInfo">DOI 10.1145/2810103.2813707</span>, <time datetime="2015-10" class="refDate">October 2015</time>, <span>&lt;<a href="https://doi.org/10.1145/2810103.2813707">https://doi.org/10.1145/2810103.2813707</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Multiple-Encryption">[Multiple-Encryption]</dt>
        <dd>
<span class="refAuthor">Merkle, R.</span> and <span class="refAuthor">M. Hellman</span>, <span class="refTitle">"On the security of multiple encryption"</span>, <span class="refContent">Communications of the ACM, Vol. 24, Issue 7, pp. 465-467</span>, <span class="seriesInfo">DOI 10.1145/358699.358718</span>, <time datetime="1981-07" class="refDate">July 1981</time>, <span>&lt;<a href="https://doi.org/10.1145/358699.358718">https://doi.org/10.1145/358699.358718</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="NIST.SP.800-56A">[NIST.SP.800-56A]</dt>
        <dd>
<span class="refAuthor">National Institute of Standards and Technology</span>, <span class="refTitle">"Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography"</span>, <span class="refContent">Revision 3</span>, <span class="seriesInfo">NIST Special Publication 800-56A</span>, <span class="seriesInfo">DOI 10.6028/NIST.SP.800-56Ar3</span>, <time datetime="2018-04" class="refDate">April 2018</time>, <span>&lt;<a href="https://doi.org/10.6028/NIST.SP.800-56Ar3">https://doi.org/10.6028/NIST.SP.800-56Ar3</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="PatersonRS11">[PatersonRS11]</dt>
        <dd>
<span class="refAuthor">Paterson, K.</span>, <span class="refAuthor">Ristenpart, T.</span>, and <span class="refAuthor">T. Shrimpton</span>, <span class="refTitle">"Tag Size Does Matter: Attacks and Proofs for the TLS Record Protocol"</span>, <span class="refContent">Proceedings of the 17th International conference on The Theory and Application of Cryptology and Information Security, pp. 372-389</span>, <span class="seriesInfo">DOI 10.1007/978-3-642-25385-0_20</span>, <time datetime="2011-12" class="refDate">December 2011</time>, <span>&lt;<a href="https://doi.org/10.1007/978-3-642-25385-0_20">https://doi.org/10.1007/978-3-642-25385-0_20</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Poddebniak2017">[Poddebniak2017]</dt>
        <dd>
<span class="refAuthor">Poddebniak, D.</span>, <span class="refAuthor">Somorovsky, J.</span>, <span class="refAuthor">Schinzel, S.</span>, <span class="refAuthor">Lochter, M.</span>, and <span class="refAuthor">P. Rösler</span>, <span class="refTitle">"Attacking Deterministic Signature Schemes using Fault Attacks"</span>, <span class="refContent">Conference: 2018 IEEE European Symposium on Security and Privacy</span>, <span class="seriesInfo">DOI 10.1109/EuroSP.2018.00031</span>, <time datetime="2018-04" class="refDate">April 2018</time>, <span>&lt;<a href="https://eprint.iacr.org/2017/1014.pdf">https://eprint.iacr.org/2017/1014.pdf</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="POODLE">[POODLE]</dt>
        <dd>
<span class="refAuthor">US-CERT</span>, <span class="refTitle">"SSL 3.0 Protocol Vulnerability and POODLE Attack"</span>, <time datetime="2014-10" class="refDate">October 2014</time>, <span>&lt;<a href="https://www.us-cert.gov/ncas/alerts/TA14-290A">https://www.us-cert.gov/ncas/alerts/TA14-290A</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RACCOON">[RACCOON]</dt>
        <dd>
<span class="refAuthor">Merget, R.</span>, <span class="refAuthor">Brinkmann, M.</span>, <span class="refAuthor">Aviram, N.</span>, <span class="refAuthor">Somorovsky, J.</span>, <span class="refAuthor">Mittmann, J.</span>, and <span class="refAuthor">J. Schwenk</span>, <span class="refTitle">"Raccoon Attack: Finding and Exploiting Most-Significant-Bit-Oracles in TLS-DH(E)"</span>, <span class="refContent">30th USENIX Security Symposium (USENIX Security 21)</span>, <time datetime="2021" class="refDate">2021</time>, <span>&lt;<a href="https://www.usenix.org/conference/usenixsecurity21/presentation/merget">https://www.usenix.org/conference/usenixsecurity21/presentation/merget</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2026">[RFC2026]</dt>
        <dd>
<span class="refAuthor">Bradner, S.</span>, <span class="refTitle">"The Internet Standards Process -- Revision 3"</span>, <span class="seriesInfo">BCP 9</span>, <span class="seriesInfo">RFC 2026</span>, <span class="seriesInfo">DOI 10.17487/RFC2026</span>, <time datetime="1996-10" class="refDate">October 1996</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2026">https://www.rfc-editor.org/info/rfc2026</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2246">[RFC2246]</dt>
        <dd>
<span class="refAuthor">Dierks, T.</span> and <span class="refAuthor">C. Allen</span>, <span class="refTitle">"The TLS Protocol Version 1.0"</span>, <span class="seriesInfo">RFC 2246</span>, <span class="seriesInfo">DOI 10.17487/RFC2246</span>, <time datetime="1999-01" class="refDate">January 1999</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2246">https://www.rfc-editor.org/info/rfc2246</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3261">[RFC3261]</dt>
        <dd>
<span class="refAuthor">Rosenberg, J.</span>, <span class="refAuthor">Schulzrinne, H.</span>, <span class="refAuthor">Camarillo, G.</span>, <span class="refAuthor">Johnston, A.</span>, <span class="refAuthor">Peterson, J.</span>, <span class="refAuthor">Sparks, R.</span>, <span class="refAuthor">Handley, M.</span>, and <span class="refAuthor">E. Schooler</span>, <span class="refTitle">"SIP: Session Initiation Protocol"</span>, <span class="seriesInfo">RFC 3261</span>, <span class="seriesInfo">DOI 10.17487/RFC3261</span>, <time datetime="2002-06" class="refDate">June 2002</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3261">https://www.rfc-editor.org/info/rfc3261</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3602">[RFC3602]</dt>
        <dd>
<span class="refAuthor">Frankel, S.</span>, <span class="refAuthor">Glenn, R.</span>, and <span class="refAuthor">S. Kelly</span>, <span class="refTitle">"The AES-CBC Cipher Algorithm and Its Use with IPsec"</span>, <span class="seriesInfo">RFC 3602</span>, <span class="seriesInfo">DOI 10.17487/RFC3602</span>, <time datetime="2003-09" class="refDate">September 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3602">https://www.rfc-editor.org/info/rfc3602</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4346">[RFC4346]</dt>
        <dd>
<span class="refAuthor">Dierks, T.</span> and <span class="refAuthor">E. Rescorla</span>, <span class="refTitle">"The Transport Layer Security (TLS) Protocol Version 1.1"</span>, <span class="seriesInfo">RFC 4346</span>, <span class="seriesInfo">DOI 10.17487/RFC4346</span>, <time datetime="2006-04" class="refDate">April 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4346">https://www.rfc-editor.org/info/rfc4346</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4347">[RFC4347]</dt>
        <dd>
<span class="refAuthor">Rescorla, E.</span> and <span class="refAuthor">N. Modadugu</span>, <span class="refTitle">"Datagram Transport Layer Security"</span>, <span class="seriesInfo">RFC 4347</span>, <span class="seriesInfo">DOI 10.17487/RFC4347</span>, <time datetime="2006-04" class="refDate">April 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4347">https://www.rfc-editor.org/info/rfc4347</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4949">[RFC4949]</dt>
        <dd>
<span class="refAuthor">Shirey, R.</span>, <span class="refTitle">"Internet Security Glossary, Version 2"</span>, <span class="seriesInfo">FYI 36</span>, <span class="seriesInfo">RFC 4949</span>, <span class="seriesInfo">DOI 10.17487/RFC4949</span>, <time datetime="2007-08" class="refDate">August 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4949">https://www.rfc-editor.org/info/rfc4949</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5077">[RFC5077]</dt>
        <dd>
<span class="refAuthor">Salowey, J.</span>, <span class="refAuthor">Zhou, H.</span>, <span class="refAuthor">Eronen, P.</span>, and <span class="refAuthor">H. Tschofenig</span>, <span class="refTitle">"Transport Layer Security (TLS) Session Resumption without Server-Side State"</span>, <span class="seriesInfo">RFC 5077</span>, <span class="seriesInfo">DOI 10.17487/RFC5077</span>, <time datetime="2008-01" class="refDate">January 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5077">https://www.rfc-editor.org/info/rfc5077</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5116">[RFC5116]</dt>
        <dd>
<span class="refAuthor">McGrew, D.</span>, <span class="refTitle">"An Interface and Algorithms for Authenticated Encryption"</span>, <span class="seriesInfo">RFC 5116</span>, <span class="seriesInfo">DOI 10.17487/RFC5116</span>, <time datetime="2008-01" class="refDate">January 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5116">https://www.rfc-editor.org/info/rfc5116</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5280">[RFC5280]</dt>
        <dd>
<span class="refAuthor">Cooper, D.</span>, <span class="refAuthor">Santesson, S.</span>, <span class="refAuthor">Farrell, S.</span>, <span class="refAuthor">Boeyen, S.</span>, <span class="refAuthor">Housley, R.</span>, and <span class="refAuthor">W. Polk</span>, <span class="refTitle">"Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile"</span>, <span class="seriesInfo">RFC 5280</span>, <span class="seriesInfo">DOI 10.17487/RFC5280</span>, <time datetime="2008-05" class="refDate">May 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5280">https://www.rfc-editor.org/info/rfc5280</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5321">[RFC5321]</dt>
        <dd>
<span class="refAuthor">Klensin, J.</span>, <span class="refTitle">"Simple Mail Transfer Protocol"</span>, <span class="seriesInfo">RFC 5321</span>, <span class="seriesInfo">DOI 10.17487/RFC5321</span>, <time datetime="2008-10" class="refDate">October 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5321">https://www.rfc-editor.org/info/rfc5321</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6101">[RFC6101]</dt>
        <dd>
<span class="refAuthor">Freier, A.</span>, <span class="refAuthor">Karlton, P.</span>, and <span class="refAuthor">P. Kocher</span>, <span class="refTitle">"The Secure Sockets Layer (SSL) Protocol Version 3.0"</span>, <span class="seriesInfo">RFC 6101</span>, <span class="seriesInfo">DOI 10.17487/RFC6101</span>, <time datetime="2011-08" class="refDate">August 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6101">https://www.rfc-editor.org/info/rfc6101</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6120">[RFC6120]</dt>
        <dd>
<span class="refAuthor">Saint-Andre, P.</span>, <span class="refTitle">"Extensible Messaging and Presence Protocol (XMPP): Core"</span>, <span class="seriesInfo">RFC 6120</span>, <span class="seriesInfo">DOI 10.17487/RFC6120</span>, <time datetime="2011-03" class="refDate">March 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6120">https://www.rfc-editor.org/info/rfc6120</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6698">[RFC6698]</dt>
        <dd>
<span class="refAuthor">Hoffman, P.</span> and <span class="refAuthor">J. Schlyter</span>, <span class="refTitle">"The DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS) Protocol: TLSA"</span>, <span class="seriesInfo">RFC 6698</span>, <span class="seriesInfo">DOI 10.17487/RFC6698</span>, <time datetime="2012-08" class="refDate">August 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6698">https://www.rfc-editor.org/info/rfc6698</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6797">[RFC6797]</dt>
        <dd>
<span class="refAuthor">Hodges, J.</span>, <span class="refAuthor">Jackson, C.</span>, and <span class="refAuthor">A. Barth</span>, <span class="refTitle">"HTTP Strict Transport Security (HSTS)"</span>, <span class="seriesInfo">RFC 6797</span>, <span class="seriesInfo">DOI 10.17487/RFC6797</span>, <time datetime="2012-11" class="refDate">November 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6797">https://www.rfc-editor.org/info/rfc6797</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6960">[RFC6960]</dt>
        <dd>
<span class="refAuthor">Santesson, S.</span>, <span class="refAuthor">Myers, M.</span>, <span class="refAuthor">Ankney, R.</span>, <span class="refAuthor">Malpani, A.</span>, <span class="refAuthor">Galperin, S.</span>, and <span class="refAuthor">C. Adams</span>, <span class="refTitle">"X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP"</span>, <span class="seriesInfo">RFC 6960</span>, <span class="seriesInfo">DOI 10.17487/RFC6960</span>, <time datetime="2013-06" class="refDate">June 2013</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6960">https://www.rfc-editor.org/info/rfc6960</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6961">[RFC6961]</dt>
        <dd>
<span class="refAuthor">Pettersen, Y.</span>, <span class="refTitle">"The Transport Layer Security (TLS) Multiple Certificate Status Request Extension"</span>, <span class="seriesInfo">RFC 6961</span>, <span class="seriesInfo">DOI 10.17487/RFC6961</span>, <time datetime="2013-06" class="refDate">June 2013</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6961">https://www.rfc-editor.org/info/rfc6961</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7228">[RFC7228]</dt>
        <dd>
<span class="refAuthor">Bormann, C.</span>, <span class="refAuthor">Ersue, M.</span>, and <span class="refAuthor">A. Keranen</span>, <span class="refTitle">"Terminology for Constrained-Node Networks"</span>, <span class="seriesInfo">RFC 7228</span>, <span class="seriesInfo">DOI 10.17487/RFC7228</span>, <time datetime="2014-05" class="refDate">May 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7228">https://www.rfc-editor.org/info/rfc7228</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7435">[RFC7435]</dt>
        <dd>
<span class="refAuthor">Dukhovni, V.</span>, <span class="refTitle">"Opportunistic Security: Some Protection Most of the Time"</span>, <span class="seriesInfo">RFC 7435</span>, <span class="seriesInfo">DOI 10.17487/RFC7435</span>, <time datetime="2014-12" class="refDate">December 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7435">https://www.rfc-editor.org/info/rfc7435</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7457">[RFC7457]</dt>
        <dd>
<span class="refAuthor">Sheffer, Y.</span>, <span class="refAuthor">Holz, R.</span>, and <span class="refAuthor">P. Saint-Andre</span>, <span class="refTitle">"Summarizing Known Attacks on Transport Layer Security (TLS) and Datagram TLS (DTLS)"</span>, <span class="seriesInfo">RFC 7457</span>, <span class="seriesInfo">DOI 10.17487/RFC7457</span>, <time datetime="2015-02" class="refDate">February 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7457">https://www.rfc-editor.org/info/rfc7457</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7507">[RFC7507]</dt>
        <dd>
<span class="refAuthor">Moeller, B.</span> and <span class="refAuthor">A. Langley</span>, <span class="refTitle">"TLS Fallback Signaling Cipher Suite Value (SCSV) for Preventing Protocol Downgrade Attacks"</span>, <span class="seriesInfo">RFC 7507</span>, <span class="seriesInfo">DOI 10.17487/RFC7507</span>, <time datetime="2015-04" class="refDate">April 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7507">https://www.rfc-editor.org/info/rfc7507</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7525">[RFC7525]</dt>
        <dd>
<span class="refAuthor">Sheffer, Y.</span>, <span class="refAuthor">Holz, R.</span>, and <span class="refAuthor">P. Saint-Andre</span>, <span class="refTitle">"Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)"</span>, <span class="seriesInfo">BCP 195</span>, <span class="seriesInfo">RFC 7525</span>, <span class="seriesInfo">DOI 10.17487/RFC7525</span>, <time datetime="2015-05" class="refDate">May 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7525">https://www.rfc-editor.org/info/rfc7525</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7568">[RFC7568]</dt>
        <dd>
<span class="refAuthor">Barnes, R.</span>, <span class="refAuthor">Thomson, M.</span>, <span class="refAuthor">Pironti, A.</span>, and <span class="refAuthor">A. Langley</span>, <span class="refTitle">"Deprecating Secure Sockets Layer Version 3.0"</span>, <span class="seriesInfo">RFC 7568</span>, <span class="seriesInfo">DOI 10.17487/RFC7568</span>, <time datetime="2015-06" class="refDate">June 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7568">https://www.rfc-editor.org/info/rfc7568</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7590">[RFC7590]</dt>
        <dd>
<span class="refAuthor">Saint-Andre, P.</span> and <span class="refAuthor">T. Alkemade</span>, <span class="refTitle">"Use of Transport Layer Security (TLS) in the Extensible Messaging and Presence Protocol (XMPP)"</span>, <span class="seriesInfo">RFC 7590</span>, <span class="seriesInfo">DOI 10.17487/RFC7590</span>, <time datetime="2015-06" class="refDate">June 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7590">https://www.rfc-editor.org/info/rfc7590</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7633">[RFC7633]</dt>
        <dd>
<span class="refAuthor">Hallam-Baker, P.</span>, <span class="refTitle">"X.509v3 Transport Layer Security (TLS) Feature Extension"</span>, <span class="seriesInfo">RFC 7633</span>, <span class="seriesInfo">DOI 10.17487/RFC7633</span>, <time datetime="2015-10" class="refDate">October 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7633">https://www.rfc-editor.org/info/rfc7633</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7672">[RFC7672]</dt>
        <dd>
<span class="refAuthor">Dukhovni, V.</span> and <span class="refAuthor">W. Hardaker</span>, <span class="refTitle">"SMTP Security via Opportunistic DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS)"</span>, <span class="seriesInfo">RFC 7672</span>, <span class="seriesInfo">DOI 10.17487/RFC7672</span>, <time datetime="2015-10" class="refDate">October 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7672">https://www.rfc-editor.org/info/rfc7672</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7673">[RFC7673]</dt>
        <dd>
<span class="refAuthor">Finch, T.</span>, <span class="refAuthor">Miller, M.</span>, and <span class="refAuthor">P. Saint-Andre</span>, <span class="refTitle">"Using DNS-Based Authentication of Named Entities (DANE) TLSA Records with SRV Records"</span>, <span class="seriesInfo">RFC 7673</span>, <span class="seriesInfo">DOI 10.17487/RFC7673</span>, <time datetime="2015-10" class="refDate">October 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7673">https://www.rfc-editor.org/info/rfc7673</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7712">[RFC7712]</dt>
        <dd>
<span class="refAuthor">Saint-Andre, P.</span>, <span class="refAuthor">Miller, M.</span>, and <span class="refAuthor">P. Hancke</span>, <span class="refTitle">"Domain Name Associations (DNA) in the Extensible Messaging and Presence Protocol (XMPP)"</span>, <span class="seriesInfo">RFC 7712</span>, <span class="seriesInfo">DOI 10.17487/RFC7712</span>, <time datetime="2015-11" class="refDate">November 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7712">https://www.rfc-editor.org/info/rfc7712</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7919">[RFC7919]</dt>
        <dd>
<span class="refAuthor">Gillmor, D.</span>, <span class="refTitle">"Negotiated Finite Field Diffie-Hellman Ephemeral Parameters for Transport Layer Security (TLS)"</span>, <span class="seriesInfo">RFC 7919</span>, <span class="seriesInfo">DOI 10.17487/RFC7919</span>, <time datetime="2016-08" class="refDate">August 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7919">https://www.rfc-editor.org/info/rfc7919</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7924">[RFC7924]</dt>
        <dd>
<span class="refAuthor">Santesson, S.</span> and <span class="refAuthor">H. Tschofenig</span>, <span class="refTitle">"Transport Layer Security (TLS) Cached Information Extension"</span>, <span class="seriesInfo">RFC 7924</span>, <span class="seriesInfo">DOI 10.17487/RFC7924</span>, <time datetime="2016-07" class="refDate">July 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7924">https://www.rfc-editor.org/info/rfc7924</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7925">[RFC7925]</dt>
        <dd>
<span class="refAuthor">Tschofenig, H., Ed.</span> and <span class="refAuthor">T. Fossati</span>, <span class="refTitle">"Transport Layer Security (TLS) / Datagram Transport Layer Security (DTLS) Profiles for the Internet of Things"</span>, <span class="seriesInfo">RFC 7925</span>, <span class="seriesInfo">DOI 10.17487/RFC7925</span>, <time datetime="2016-07" class="refDate">July 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7925">https://www.rfc-editor.org/info/rfc7925</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8452">[RFC8452]</dt>
        <dd>
<span class="refAuthor">Gueron, S.</span>, <span class="refAuthor">Langley, A.</span>, and <span class="refAuthor">Y. Lindell</span>, <span class="refTitle">"AES-GCM-SIV: Nonce Misuse-Resistant Authenticated Encryption"</span>, <span class="seriesInfo">RFC 8452</span>, <span class="seriesInfo">DOI 10.17487/RFC8452</span>, <time datetime="2019-04" class="refDate">April 2019</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8452">https://www.rfc-editor.org/info/rfc8452</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8461">[RFC8461]</dt>
        <dd>
<span class="refAuthor">Margolis, D.</span>, <span class="refAuthor">Risher, M.</span>, <span class="refAuthor">Ramakrishnan, B.</span>, <span class="refAuthor">Brotman, A.</span>, and <span class="refAuthor">J. Jones</span>, <span class="refTitle">"SMTP MTA Strict Transport Security (MTA-STS)"</span>, <span class="seriesInfo">RFC 8461</span>, <span class="seriesInfo">DOI 10.17487/RFC8461</span>, <time datetime="2018-09" class="refDate">September 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8461">https://www.rfc-editor.org/info/rfc8461</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8470">[RFC8470]</dt>
        <dd>
<span class="refAuthor">Thomson, M.</span>, <span class="refAuthor">Nottingham, M.</span>, and <span class="refAuthor">W. Tarreau</span>, <span class="refTitle">"Using Early Data in HTTP"</span>, <span class="seriesInfo">RFC 8470</span>, <span class="seriesInfo">DOI 10.17487/RFC8470</span>, <time datetime="2018-09" class="refDate">September 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8470">https://www.rfc-editor.org/info/rfc8470</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8879">[RFC8879]</dt>
        <dd>
<span class="refAuthor">Ghedini, A.</span> and <span class="refAuthor">V. Vasiliev</span>, <span class="refTitle">"TLS Certificate Compression"</span>, <span class="seriesInfo">RFC 8879</span>, <span class="seriesInfo">DOI 10.17487/RFC8879</span>, <time datetime="2020-12" class="refDate">December 2020</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8879">https://www.rfc-editor.org/info/rfc8879</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9000">[RFC9000]</dt>
        <dd>
<span class="refAuthor">Iyengar, J., Ed.</span> and <span class="refAuthor">M. Thomson, Ed.</span>, <span class="refTitle">"QUIC: A UDP-Based Multiplexed and Secure Transport"</span>, <span class="seriesInfo">RFC 9000</span>, <span class="seriesInfo">DOI 10.17487/RFC9000</span>, <time datetime="2021-05" class="refDate">May 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc9000">https://www.rfc-editor.org/info/rfc9000</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9001">[RFC9001]</dt>
        <dd>
<span class="refAuthor">Thomson, M., Ed.</span> and <span class="refAuthor">S. Turner, Ed.</span>, <span class="refTitle">"Using TLS to Secure QUIC"</span>, <span class="seriesInfo">RFC 9001</span>, <span class="seriesInfo">DOI 10.17487/RFC9001</span>, <time datetime="2021-05" class="refDate">May 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc9001">https://www.rfc-editor.org/info/rfc9001</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9051">[RFC9051]</dt>
        <dd>
<span class="refAuthor">Melnikov, A., Ed.</span> and <span class="refAuthor">B. Leiba, Ed.</span>, <span class="refTitle">"Internet Message Access Protocol (IMAP) - Version 4rev2"</span>, <span class="seriesInfo">RFC 9051</span>, <span class="seriesInfo">DOI 10.17487/RFC9051</span>, <time datetime="2021-08" class="refDate">August 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc9051">https://www.rfc-editor.org/info/rfc9051</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9110">[RFC9110]</dt>
        <dd>
<span class="refAuthor">Fielding, R., Ed.</span>, <span class="refAuthor">Nottingham, M., Ed.</span>, and <span class="refAuthor">J. Reschke, Ed.</span>, <span class="refTitle">"HTTP Semantics"</span>, <span class="seriesInfo">STD 97</span>, <span class="seriesInfo">RFC 9110</span>, <span class="seriesInfo">DOI 10.17487/RFC9110</span>, <time datetime="2022-06" class="refDate">June 2022</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc9110">https://www.rfc-editor.org/info/rfc9110</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9112">[RFC9112]</dt>
        <dd>
<span class="refAuthor">Fielding, R., Ed.</span>, <span class="refAuthor">Nottingham, M., Ed.</span>, and <span class="refAuthor">J. Reschke, Ed.</span>, <span class="refTitle">"HTTP/1.1"</span>, <span class="seriesInfo">STD 99</span>, <span class="seriesInfo">RFC 9112</span>, <span class="seriesInfo">DOI 10.17487/RFC9112</span>, <time datetime="2022-06" class="refDate">June 2022</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc9112">https://www.rfc-editor.org/info/rfc9112</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9113">[RFC9113]</dt>
        <dd>
<span class="refAuthor">Thomson, M., Ed.</span> and <span class="refAuthor">C. Benfield, Ed.</span>, <span class="refTitle">"HTTP/2"</span>, <span class="seriesInfo">RFC 9113</span>, <span class="seriesInfo">DOI 10.17487/RFC9113</span>, <time datetime="2022-06" class="refDate">June 2022</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc9113">https://www.rfc-editor.org/info/rfc9113</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9162">[RFC9162]</dt>
        <dd>
<span class="refAuthor">Laurie, B.</span>, <span class="refAuthor">Messeri, E.</span>, and <span class="refAuthor">R. Stradling</span>, <span class="refTitle">"Certificate Transparency Version 2.0"</span>, <span class="seriesInfo">RFC 9162</span>, <span class="seriesInfo">DOI 10.17487/RFC9162</span>, <time datetime="2021-12" class="refDate">December 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc9162">https://www.rfc-editor.org/info/rfc9162</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9191">[RFC9191]</dt>
        <dd>
<span class="refAuthor">Sethi, M.</span>, <span class="refAuthor">Preuß Mattsson, J.</span>, and <span class="refAuthor">S. Turner</span>, <span class="refTitle">"Handling Large Certificates and Long Certificate Chains in TLS-Based EAP Methods"</span>, <span class="seriesInfo">RFC 9191</span>, <span class="seriesInfo">DOI 10.17487/RFC9191</span>, <time datetime="2022-02" class="refDate">February 2022</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc9191">https://www.rfc-editor.org/info/rfc9191</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="SAFECURVES">[SAFECURVES]</dt>
        <dd>
<span class="refAuthor">Bernstein, D. J.</span> and <span class="refAuthor">T. Lange</span>, <span class="refTitle">"SafeCurves: choosing safe curves for elliptic-curve cryptography"</span>, <time datetime="2014-12" class="refDate">December 2014</time>, <span>&lt;<a href="https://safecurves.cr.yp.to">https://safecurves.cr.yp.to</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Soghoian2011">[Soghoian2011]</dt>
        <dd>
<span class="refAuthor">Soghoian, C.</span> and <span class="refAuthor">S. Stamm</span>, <span class="refTitle">"Certified Lies: Detecting and Defeating Government Interception Attacks Against SSL"</span>, <span class="refContent">SSRN Electronic Journal</span>, <span class="seriesInfo">DOI 10.2139/ssrn.1591033</span>, <time datetime="2010-04" class="refDate">April 2010</time>, <span>&lt;<a href="https://doi.org/10.2139/ssrn.1591033">https://doi.org/10.2139/ssrn.1591033</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Springall16">[Springall16]</dt>
        <dd>
<span class="refAuthor">Springall, D.</span>, <span class="refAuthor">Durumeric, Z.</span>, and <span class="refAuthor">J. Halderman</span>, <span class="refTitle">"Measuring the Security Harm of TLS Crypto Shortcuts"</span>, <span class="refContent">Proceedings of the 2016 Internet Measurement Conference, pp. 33-47</span>, <span class="seriesInfo">DOI 10.1145/2987443.2987480</span>, <time datetime="2016-11" class="refDate">November 2016</time>, <span>&lt;<a href="https://doi.org/10.1145/2987443.2987480">https://doi.org/10.1145/2987443.2987480</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="STD53">[STD53]</dt>
        <dd>
<div class="refInstance" id="RFC1939">
            <span class="refAuthor">Myers, J.</span> and <span class="refAuthor">M. Rose</span>, <span class="refTitle">"Post Office Protocol - Version 3"</span>, <span class="seriesInfo">STD 53</span>, <span class="seriesInfo">RFC 1939</span>, <time datetime="1996-05" class="refDate">May 1996</time>. </div>
<span>&lt;<a href="https://www.rfc-editor.org/info/std53">https://www.rfc-editor.org/info/std53</a>&gt;</span>
</dd>
<dd class="break"></dd>
<dt id="Sy2018">[Sy2018]</dt>
        <dd>
<span class="refAuthor">Sy, E.</span>, <span class="refAuthor">Burkert, C.</span>, <span class="refAuthor">Federrath, H.</span>, and <span class="refAuthor">M. Fischer</span>, <span class="refTitle">"Tracking Users across the Web via TLS Session Resumption"</span>, <span class="refContent">Proceedings of the 34th Annual Computer Security Applications Conference, pp. 289-299</span>, <span class="seriesInfo">DOI 10.1145/3274694.3274708</span>, <time datetime="2018-12" class="refDate">December 2018</time>, <span>&lt;<a href="https://doi.org/10.1145/3274694.3274708">https://doi.org/10.1145/3274694.3274708</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="I-D.ietf-tls-esni">[TLS-ECH]</dt>
        <dd>
<span class="refAuthor">Rescorla, E.</span>, <span class="refAuthor">Oku, K.</span>, <span class="refAuthor">Sullivan, N.</span>, and <span class="refAuthor">C. A. Wood</span>, <span class="refTitle">"TLS Encrypted Client Hello"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-ietf-tls-esni-15</span>, <time datetime="2022-10-03" class="refDate">3 October 2022</time>, <span>&lt;<a href="https://datatracker.ietf.org/doc/html/draft-ietf-tls-esni-15">https://datatracker.ietf.org/doc/html/draft-ietf-tls-esni-15</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Triple-Handshake">[Triple-Handshake]</dt>
        <dd>
<span class="refAuthor">Bhargavan, K.</span>, <span class="refAuthor">Lavaud, A.</span>, <span class="refAuthor">Fournet, C.</span>, <span class="refAuthor">Pironti, A.</span>, and <span class="refAuthor">P. Strub</span>, <span class="refTitle">"Triple Handshakes and Cookie Cutters: Breaking and Fixing Authentication over TLS"</span>, <span class="refContent">2014 IEEE Symposium on Security and Privacy</span>, <span class="seriesInfo">DOI 10.1109/sp.2014.14</span>, <time datetime="2014-05" class="refDate">May 2014</time>, <span>&lt;<a href="https://doi.org/10.1109/sp.2014.14">https://doi.org/10.1109/sp.2014.14</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="TWIRL">[TWIRL]</dt>
      <dd>
<span class="refAuthor">Shamir, A.</span> and <span class="refAuthor">E. Tromer</span>, <span class="refTitle">"Factoring Large Numbers with the TWIRL Device"</span>, <span class="refContent">2014 IEEE Symposium on Security and Privacy</span>, <span class="seriesInfo">DOI 10.1007/978-3-540-45146-4_1</span>, <time datetime="2004" class="refDate">2004</time>, <span>&lt;<a href="https://cs.tau.ac.il/~tromer/papers/twirl.pdf">https://cs.tau.ac.il/~tromer/papers/twirl.pdf</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
</section>
<div id="diff-rfc">
<section id="appendix-A">
      <h2 id="name-differences-from-rfc-7525">
<a href="#appendix-A" class="section-number selfRef">Appendix A. </a><a href="#name-differences-from-rfc-7525" class="section-name selfRef">Differences from RFC 7525</a>
      </h2>
<p id="appendix-A-1">This revision of the Best Current Practices contains numerous changes, and this section is focused
on the normative changes.<a href="#appendix-A-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="appendix-A-2.1">
          <p id="appendix-A-2.1.1">High-level differences:<a href="#appendix-A-2.1.1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="appendix-A-2.1.2.1">Described the expectations from new TLS-incorporating transport protocols and from new application protocols layered on TLS.<a href="#appendix-A-2.1.2.1" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.2">Clarified items (e.g., renegotiation) that only apply to TLS 1.2.<a href="#appendix-A-2.1.2.2" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.3">Changed the status of TLS 1.0 and 1.1 from "<span class="bcp14">SHOULD NOT</span>" to "<span class="bcp14">MUST NOT</span>".<a href="#appendix-A-2.1.2.3" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.4">Added TLS 1.3 at a "<span class="bcp14">SHOULD</span>" level.<a href="#appendix-A-2.1.2.4" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.5">Made similar changes to DTLS.<a href="#appendix-A-2.1.2.5" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.6">Included specific guidance for multiplexed protocols.<a href="#appendix-A-2.1.2.6" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.7">
              <span class="bcp14">MUST</span>-level implementation requirement for ALPN and more specific <span class="bcp14">SHOULD</span>-level guidance for ALPN and SNI.<a href="#appendix-A-2.1.2.7" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.8">Clarified discussion of strict TLS policies, including <span class="bcp14">MUST</span>-level recommendations.<a href="#appendix-A-2.1.2.8" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.9">Limits on key usage.<a href="#appendix-A-2.1.2.9" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.10">New attacks since <span>[<a href="#RFC7457" class="cite xref">RFC7457</a>]</span>: ALPACA, Raccoon, Logjam, and "Nonce-Disrespecting Adversaries".<a href="#appendix-A-2.1.2.10" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.11">RFC 6961 (OCSP status_request_v2) has been deprecated.<a href="#appendix-A-2.1.2.11" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.1.2.12">
              <span class="bcp14">MUST</span>-level requirement for server-side RSA certificates to have a 2048-bit modulus at a minimum, replacing a "<span class="bcp14">SHOULD</span>".<a href="#appendix-A-2.1.2.12" class="pilcrow">¶</a>
</li>
          </ul>
</li>
        <li class="normal" id="appendix-A-2.2">
          <p id="appendix-A-2.2.1">Differences specific to TLS 1.2:<a href="#appendix-A-2.2.1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="appendix-A-2.2.2.1">
              <span class="bcp14">SHOULD</span>-level guidance on AES-GCM nonce generation.<a href="#appendix-A-2.2.2.1" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.2">
              <span class="bcp14">SHOULD NOT</span> use (static or ephemeral) finite-field DH key agreement.<a href="#appendix-A-2.2.2.2" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.3">
              <span class="bcp14">SHOULD NOT</span> reuse ephemeral finite-field DH keys across multiple connections.<a href="#appendix-A-2.2.2.3" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.4">
              <span class="bcp14">SHOULD NOT</span> use static Elliptic Curve DH key exchange.<a href="#appendix-A-2.2.2.4" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.5">2048-bit DH is now a "<span class="bcp14">MUST</span>" and ECDH minimal curve size is 224 (vs. 192 previously).<a href="#appendix-A-2.2.2.5" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.6">Support for <code>extended_master_secret</code> is now a "<span class="bcp14">MUST</span>" (previously it was a soft recommendation, as the RFC had not been published at the time). Also removed other, more complicated, related mitigations.<a href="#appendix-A-2.2.2.6" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.7">
              <span class="bcp14">MUST</span>-level restriction on session ticket validity, replacing a "<span class="bcp14">SHOULD</span>".<a href="#appendix-A-2.2.2.7" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.8">
              <span class="bcp14">SHOULD</span>-level restriction on the TLS session duration, depending on the rotation period of an <span>[<a href="#RFC5077" class="cite xref">RFC5077</a>]</span> ticket key.<a href="#appendix-A-2.2.2.8" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.9">Dropped TLS_DHE_RSA_WITH_AES from the recommended ciphers.<a href="#appendix-A-2.2.2.9" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.10">Added TLS_ECDHE_ECDSA_WITH_AES to the recommended ciphers.<a href="#appendix-A-2.2.2.10" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.11">
              <span class="bcp14">SHOULD NOT</span> use the old MTI cipher suite, TLS_RSA_WITH_AES_128_CBC_SHA.<a href="#appendix-A-2.2.2.11" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.2.2.12">Recommended curve X25519 alongside NIST P-256.<a href="#appendix-A-2.2.2.12" class="pilcrow">¶</a>
</li>
          </ul>
</li>
        <li class="normal" id="appendix-A-2.3">
          <p id="appendix-A-2.3.1">Differences specific to TLS 1.3:<a href="#appendix-A-2.3.1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="appendix-A-2.3.2.1">New TLS 1.3 capabilities: 0-RTT.<a href="#appendix-A-2.3.2.1" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.3.2.2">Removed capabilities: renegotiation and compression.<a href="#appendix-A-2.3.2.2" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.3.2.3">Added mention of TLS Encrypted Client Hello, but no recommendation for use until it is finalized.<a href="#appendix-A-2.3.2.3" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.3.2.4">
              <span class="bcp14">SHOULD</span>-level requirement for forward secrecy in TLS 1.3 session resumption.<a href="#appendix-A-2.3.2.4" class="pilcrow">¶</a>
</li>
            <li class="normal" id="appendix-A-2.3.2.5">Generic <span class="bcp14">MUST</span>-level guidance to avoid 0-RTT unless it is documented for the particular protocol.<a href="#appendix-A-2.3.2.5" class="pilcrow">¶</a>
</li>
          </ul>
</li>
      </ul>
</section>
</div>
<div id="acknowledgments">
<section id="appendix-B">
      <h2 id="name-acknowledgments">
<a href="#name-acknowledgments" class="section-name selfRef">Acknowledgments</a>
      </h2>
<p id="appendix-B-1">Thanks to
<span class="contact-name">Alexey Melnikov</span>,
<span class="contact-name">Alvaro Retana</span>,
<span class="contact-name">Andrei Popov</span>,
<span class="contact-name">Ben Kaduk</span>,
<span class="contact-name">Christian Huitema</span>,
<span class="contact-name">Corey Bonnell</span>,
<span class="contact-name">Cullen Jennings</span>,
<span class="contact-name">Daniel Kahn Gillmor</span>,
<span class="contact-name">David Benjamin</span>,
<span class="contact-name">Eric Rescorla</span>,
<span class="contact-name">Éric Vyncke</span>,
<span class="contact-name">Francesca Palombini</span>,
<span class="contact-name">Hannes Tschofenig</span>,
<span class="contact-name">Hubert Kario</span>,
<span class="contact-name">Ilari Liusvaara</span>,
<span class="contact-name">John Preuß Mattsson</span>,
<span class="contact-name">John R. Levine</span>,
<span class="contact-name">Julien Élie</span>,
<span class="contact-name">Lars Eggert</span>,
<span class="contact-name">Leif Johansson</span>,
<span class="contact-name">Magnus Westerlund</span>,
<span class="contact-name">Martin Duke</span>,
<span class="contact-name">Martin Thomson</span>,
<span class="contact-name">Mohit Sahni</span>,
<span class="contact-name">Nick Sullivan</span>,
<span class="contact-name">Nimrod Aviram</span>,
<span class="contact-name">Paul Wouters</span>,
<span class="contact-name">Peter Gutmann</span>,
<span class="contact-name">Rich Salz</span>,
<span class="contact-name">Robert Sayre</span>,
<span class="contact-name">Robert Wilton</span>,
<span class="contact-name">Roman Danyliw</span>,
<span class="contact-name">Ryan Sleevi</span>,
<span class="contact-name">Sean Turner</span>,
<span class="contact-name">Stephen Farrell</span>,
<span class="contact-name">Tim Evans</span>,
<span class="contact-name">Valery Smyslov</span>,
<span class="contact-name">Viktor Dukhovni</span>,
and <span class="contact-name">Warren Kumari</span>
for helpful comments and discussions that have shaped this document.<a href="#appendix-B-1" class="pilcrow">¶</a></p>
<p id="appendix-B-2">The authors gratefully acknowledge the contribution of <span class="contact-name">Ralph Holz</span>, who was a coauthor of RFC 7525, the previous version of the TLS recommendations.<a href="#appendix-B-2" class="pilcrow">¶</a></p>
<p id="appendix-B-3">See RFC 7525 for additional acknowledgments specific to the previous version of the TLS recommendations.<a href="#appendix-B-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="authors-addresses">
<section id="appendix-C">
      <h2 id="name-authors-addresses">
<a href="#name-authors-addresses" class="section-name selfRef">Authors' Addresses</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Yaron Sheffer</span></div>
<div dir="auto" class="left"><span class="org">Intuit</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:yaronf.ietf@gmail.com" class="email">yaronf.ietf@gmail.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Peter Saint-Andre</span></div>
<div dir="auto" class="left"><span class="org">Independent</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:stpeter@stpeter.im" class="email">stpeter@stpeter.im</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Thomas Fossati</span></div>
<div dir="auto" class="left"><span class="org">ARM Limited</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:thomas.fossati@arm.com" class="email">thomas.fossati@arm.com</a>
</div>
</address>
</section>
</div>
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