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<!DOCTYPE html>
<html lang="en" class="RFC">
<head>
<meta charset="utf-8">
<meta content="Common,Latin" name="scripts">
<meta content="initial-scale=1.0" name="viewport">
<title>RFC 8739: Support for Short-Term, Automatically Renewed (STAR) Certificates in the Automated Certificate Management Environment (ACME)</title>
<meta content="Yaron Sheffer" name="author">
<meta content="Diego Lopez" name="author">
<meta content="Oscar Gonzalez de Dios" name="author">
<meta content="Antonio Agustin Pastor Perales" name="author">
<meta content="Thomas Fossati" name="author">
<meta content="
       Public key certificates need to be revoked when they are compromised,
      that is, when the associated private key is exposed to an unauthorized
      entity.  However, the revocation process is often unreliable. An
      alternative to revocation is issuing a sequence of certificates, each
      with a short validity period, and terminating the sequence upon
      compromise.  This memo proposes an Automated Certificate Management
      Environment (ACME) extension to enable the issuance of Short-Term,
      Automatically Renewed (STAR) X.509 certificates. 
    " name="description">
<meta content="xml2rfc 2.40.1" name="generator">
<meta content="OCSP" name="keyword">
<meta content="CRL" name="keyword">
<meta content="revocation" name="keyword">
<meta content="8739" name="rfc.number">
<link href="rfc8739.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 necssary 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;
}
h5, h6 {
  font-size: 14px;
}
#n-copyright-notice {
  border-bottom: 1px solid #ddd;
  padding-bottom: 1em;
  margin-bottom: 1em;
}
/* general structure */
p {
  padding: 0;
  margin: 0 0 1em 0;
  text-align: left;
}
div, span {
  position: relative;
}
div {
  margin: 0;
}
.alignRight.art-text {
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  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignRight.art-text pre {
  padding: 0;
}
.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 {
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}
.alignCenter.art-text {
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  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 {
  border: none;
  /* this isn't optimal, but it's an existence proof.  PrinceXML doesn't
     support flexbox yet.
  */
  display: table;
  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 {
  list-style-type: none;
}
ul.empty li, .ulEmpty li {
  margin-top: 0.5em;
}
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, code {
  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;
}
#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;
  }
  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 follwing 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, code {
  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 informatio 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;
  }

}
/* Avoid wrapping of URLs in references */
@media screen {
  .references a {
    white-space: nowrap;
  }
}
/* 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 {
  margin: 1em 0 0 0;
}
/* In print, the pilcrow won't show on hover, so prevent it from taking up space,
   possibly even requiring a new line */
@media print {
  a.pilcrow {
    display: none;
  }
}
/* Styling for the external metadata */
div#external-metadata {
  background-color: #eee;
  padding: 0.5em;
  margin-bottom: 0.5em;
  display: none;
}
div#internal-metadata {
  padding: 0.5em;                       /* to match the external-metadata padding */
}
/* Styling for title RFC Number */
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<link href="https://dx.doi.org/10.17487/rfc8739" rel="alternate">
  <link href="urn:issn:2070-1721" rel="alternate">
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<table class="ears">
<thead><tr>
<td class="left">RFC 8739</td>
<td class="center">Support for ACME STAR</td>
<td class="right">March 2020</td>
</tr></thead>
<tfoot><tr>
<td class="left">Sheffer, et al.</td>
<td class="center">Standards Track</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/rfc8739" class="eref">8739</a></dd>
<dt class="label-category">Category:</dt>
<dd class="category">Standards Track</dd>
<dt class="label-published">Published:</dt>
<dd class="published">
<time datetime="2020-03" class="published">March 2020</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">D. Lopez</div>
<div class="org">Telefonica I+D</div>
</div>
<div class="author">
      <div class="author-name">O. Gonzalez de Dios</div>
<div class="org">Telefonica I+D</div>
</div>
<div class="author">
      <div class="author-name">A. Pastor Perales</div>
<div class="org">Telefonica I+D</div>
</div>
<div class="author">
      <div class="author-name">T. Fossati</div>
<div class="org">ARM</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8739</h1>
<h1 id="title">Support for Short-Term, Automatically Renewed (STAR) Certificates in the Automated Certificate Management Environment (ACME)</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">Public key certificates need to be revoked when they are compromised,
      that is, when the associated private key is exposed to an unauthorized
      entity.  However, the revocation process is often unreliable. An
      alternative to revocation is issuing a sequence of certificates, each
      with a short validity period, and terminating the sequence upon
      compromise.  This memo proposes an Automated Certificate Management
      Environment (ACME) extension to enable the issuance of Short-Term,
      Automatically Renewed (STAR) X.509 certificates.<a href="#section-abstract-1" 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 is an Internet Standards Track document.<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 Internet Standards 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/rfc8739">https://www.rfc-editor.org/info/rfc8739</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) 2020 IETF Trust and the persons identified as the
            document authors. All rights reserved.<a href="#section-boilerplate.2-1" class="pilcrow">¶</a></p>
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            This document is subject to BCP 78 and the IETF Trust's Legal
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            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 Simplified BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Simplified 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="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.1">
            <p id="section-toc.1-1.1.1"><a href="#section-1" class="xref">1</a>.  <a href="#name-introduction" class="xref">Introduction</a><a href="#section-toc.1-1.1.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.1.2.1">
                <p id="section-toc.1-1.1.2.1.1"><a href="#section-1.1" class="xref">1.1</a>.  <a href="#name-name-delegation-use-case" class="xref">Name Delegation Use Case</a><a href="#section-toc.1-1.1.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.1.2.2">
                <p id="section-toc.1-1.1.2.2.1"><a href="#section-1.2" class="xref">1.2</a>.  <a href="#name-terminology" class="xref">Terminology</a><a href="#section-toc.1-1.1.2.2.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.1.2.3">
                <p id="section-toc.1-1.1.2.3.1"><a href="#section-1.3" class="xref">1.3</a>.  <a href="#name-conventions-used-in-this-do" class="xref">Conventions Used in This Document</a><a href="#section-toc.1-1.1.2.3.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.2">
            <p id="section-toc.1-1.2.1"><a href="#section-2" class="xref">2</a>.  <a href="#name-protocol-flow" class="xref">Protocol Flow</a><a href="#section-toc.1-1.2.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.2.2.1">
                <p id="section-toc.1-1.2.2.1.1"><a href="#section-2.1" class="xref">2.1</a>.  <a href="#name-bootstrap" class="xref">Bootstrap</a><a href="#section-toc.1-1.2.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.2.2.2">
                <p id="section-toc.1-1.2.2.2.1"><a href="#section-2.2" class="xref">2.2</a>.  <a href="#name-auto-renewal" class="xref">Auto Renewal</a><a href="#section-toc.1-1.2.2.2.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.2.2.3">
                <p id="section-toc.1-1.2.2.3.1"><a href="#section-2.3" class="xref">2.3</a>.  <a href="#name-termination" class="xref">Termination</a><a href="#section-toc.1-1.2.2.3.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1"><a href="#section-3" class="xref">3</a>.  <a href="#name-protocol-details" class="xref">Protocol Details</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc 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="xref">3.1</a>.  <a href="#name-acme-extensions" class="xref">ACME Extensions</a><a href="#section-toc.1-1.3.2.1.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.3.2.1.2.1">
                    <p id="section-toc.1-1.3.2.1.2.1.1"><a href="#section-3.1.1" class="xref">3.1.1</a>.  <a href="#name-extending-the-order-resourc" class="xref">Extending the Order Resource</a><a href="#section-toc.1-1.3.2.1.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc 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="xref">3.1.2</a>.  <a href="#name-canceling-an-auto-renewal-o" class="xref">Canceling an Auto-renewal Order</a><a href="#section-toc.1-1.3.2.1.2.2.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc 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="xref">3.2</a>.  <a href="#name-capability-discovery" class="xref">Capability Discovery</a><a href="#section-toc.1-1.3.2.2.1" class="pilcrow">¶</a></p>
</li>
<li class="toc 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="xref">3.3</a>.  <a href="#name-fetching-the-certificates" class="xref">Fetching the Certificates</a><a href="#section-toc.1-1.3.2.3.1" class="pilcrow">¶</a></p>
</li>
<li class="toc 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="xref">3.4</a>.  <a href="#name-negotiating-an-unauthentica" class="xref">Negotiating an Unauthenticated GET</a><a href="#section-toc.1-1.3.2.4.1" class="pilcrow">¶</a></p>
</li>
<li class="toc 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="xref">3.5</a>.  <a href="#name-computing-notbefore-and-not" class="xref">Computing notBefore and notAfter of STAR Certificates</a><a href="#section-toc.1-1.3.2.5.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.3.2.5.2.1">
                    <p id="section-toc.1-1.3.2.5.2.1.1"><a href="#section-3.5.1" class="xref">3.5.1</a>.  <a href="#name-example" class="xref">Example</a><a href="#section-toc.1-1.3.2.5.2.1.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.4">
            <p id="section-toc.1-1.4.1"><a href="#section-4" class="xref">4</a>.  <a href="#name-operational-considerations" class="xref">Operational Considerations</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc 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="xref">4.1</a>.  <a href="#name-the-meaning-of-short-term-a" class="xref">The Meaning of "Short Term" and the Impact of Skewed Clocks</a><a href="#section-toc.1-1.4.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc 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="xref">4.2</a>.  <a href="#name-impact-on-certificate-trans" class="xref">Impact on Certificate Transparency (CT) Logs</a><a href="#section-toc.1-1.4.2.2.1" class="pilcrow">¶</a></p>
</li>
<li class="toc 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="xref">4.3</a>.  <a href="#name-http-caching-and-dependabil" class="xref">HTTP Caching and Dependability</a><a href="#section-toc.1-1.4.2.3.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.5">
            <p id="section-toc.1-1.5.1"><a href="#section-5" class="xref">5</a>.  <a href="#name-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.5.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc 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="xref">5.1</a>.  <a href="#name-new-registries" class="xref">New Registries</a><a href="#section-toc.1-1.5.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc 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="xref">5.2</a>.  <a href="#name-new-error-types" class="xref">New Error Types</a><a href="#section-toc.1-1.5.2.2.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.5.2.3">
                <p id="section-toc.1-1.5.2.3.1"><a href="#section-5.3" class="xref">5.3</a>.  <a href="#name-new-fields-in-order-objects" class="xref">New Fields in Order Objects</a><a href="#section-toc.1-1.5.2.3.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.5.2.4">
                <p id="section-toc.1-1.5.2.4.1"><a href="#section-5.4" class="xref">5.4</a>.  <a href="#name-fields-in-the-auto-renewal-" class="xref">Fields in the "auto-renewal" Object within an Order Object</a><a href="#section-toc.1-1.5.2.4.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.5.2.5">
                <p id="section-toc.1-1.5.2.5.1"><a href="#section-5.5" class="xref">5.5</a>.  <a href="#name-new-fields-in-the-meta-obje" class="xref">New Fields in the "meta" Object within a Directory Object</a><a href="#section-toc.1-1.5.2.5.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.5.2.6">
                <p id="section-toc.1-1.5.2.6.1"><a href="#section-5.6" class="xref">5.6</a>.  <a href="#name-fields-in-the-auto-renewal-o" class="xref">Fields in the "auto-renewal" Object within a Directory Metadata Object</a><a href="#section-toc.1-1.5.2.6.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.5.2.7">
                <p id="section-toc.1-1.5.2.7.1"><a href="#section-5.7" class="xref">5.7</a>.  <a href="#name-cert-not-before-and-cert-no" class="xref">Cert-Not-Before and Cert-Not-After HTTP Headers</a><a href="#section-toc.1-1.5.2.7.1" class="pilcrow">¶</a></p>
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</li>
<li class="toc ulEmpty" id="section-toc.1-1.6">
            <p id="section-toc.1-1.6.1"><a href="#section-6" class="xref">6</a>.  <a href="#name-security-considerations" class="xref">Security Considerations</a><a href="#section-toc.1-1.6.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.6.2.1">
                <p id="section-toc.1-1.6.2.1.1"><a href="#section-6.1" class="xref">6.1</a>.  <a href="#name-no-revocation" class="xref">No Revocation</a><a href="#section-toc.1-1.6.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.6.2.2">
                <p id="section-toc.1-1.6.2.2.1"><a href="#section-6.2" class="xref">6.2</a>.  <a href="#name-denial-of-service-considera" class="xref">Denial-of-Service Considerations</a><a href="#section-toc.1-1.6.2.2.1" class="pilcrow">¶</a></p>
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<li class="toc ulEmpty" id="section-toc.1-1.6.2.3">
                <p id="section-toc.1-1.6.2.3.1"><a href="#section-6.3" class="xref">6.3</a>.  <a href="#name-privacy-considerations" class="xref">Privacy Considerations</a><a href="#section-toc.1-1.6.2.3.1" class="pilcrow">¶</a></p>
</li>
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<li class="toc ulEmpty" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-7" class="xref">7</a>.  <a href="#name-references" class="xref">References</a><a href="#section-toc.1-1.7.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc 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="xref">7.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a><a href="#section-toc.1-1.7.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc 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="xref">7.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a><a href="#section-toc.1-1.7.2.2.1" class="pilcrow">¶</a></p>
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            <p id="section-toc.1-1.8.1"><a href="#section-appendix.a" class="xref"></a><a href="#name-acknowledgments" class="xref">Acknowledgments</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
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            <p id="section-toc.1-1.9.1"><a href="#section-appendix.b" class="xref"></a><a href="#name-authors-addresses" class="xref">Authors' Addresses</a><a href="#section-toc.1-1.9.1" class="pilcrow">¶</a></p>
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</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">The ACME protocol <span>[<a href="#RFC8555" class="xref">RFC8555</a>]</span> automates
      the process of issuing a certificate to a named entity (an Identifier
      Owner or IdO). Typically, but not always, the identifier is a domain
      name.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">If the IdO wishes to obtain a string of short-term certificates
      originating from the same private key (see <span>[<a href="#TOPALOVIC" class="xref">TOPALOVIC</a>]</span> about why using short-lived certificates might be
      preferable to explicit revocation), she must go through the whole ACME
      protocol each time a new short-term certificate is needed, e.g., every
      2-3 days.  If done this way, the process would involve frequent
      interactions between the registration function of the ACME Certification
      Authority (CA) and the identity provider infrastructure (e.g., DNS, web
      servers), therefore making the issuance of short-term certificates
      exceedingly dependent on the reliability of both.<a href="#section-1-2" class="pilcrow">¶</a></p>
<p id="section-1-3">This document presents an extension of the ACME protocol that
      optimizes this process by making short-term certificates first-class
      objects in the ACME ecosystem.  Once the Order for a string of
      short-term certificates is accepted, the CA is responsible for
      publishing the next certificate at an agreed upon URL before the
      previous one expires.  The IdO can terminate the automatic renewal
      before the negotiated deadline if needed, e.g., on key compromise.<a href="#section-1-3" class="pilcrow">¶</a></p>
<p id="section-1-4">For a more generic treatment of STAR certificates, readers are referred to <span>[<a href="#I-D.nir-saag-star" class="xref">SHORT-TERM-CERTS</a>]</span>.<a href="#section-1-4" class="pilcrow">¶</a></p>
<div id="name-delegation-use-case">
<section id="section-1.1">
        <h3 id="name-name-delegation-use-case">
<a href="#section-1.1" class="section-number selfRef">1.1. </a><a href="#name-name-delegation-use-case" class="section-name selfRef">Name Delegation Use Case</a>
        </h3>
<p id="section-1.1-1">The proposed mechanism can be used as a building block of an
        efficient name-delegation protocol, for example, one that exists between a
        Content Distribution Network (CDN) or a cloud provider and its
        customers <span>[<a href="#I-D.ietf-acme-star-delegation" class="xref">STAR-DELEGATION</a>]</span>.  At any time, the service customer (i.e., the IdO)
        can terminate the delegation by simply instructing the CA to stop the
        automatic renewal and letting the currently active certificate expire
        shortly thereafter.<a href="#section-1.1-1" class="pilcrow">¶</a></p>
<p id="section-1.1-2">Note that in the name delegation use case, the delegated entity needs to access
the auto-renewed certificate without being in possession of the ACME account
key that was used for initiating the STAR issuance.  This leads to the optional
use of unauthenticated GET in this protocol (<a href="#certificate-get-nego" class="xref">Section 3.4</a>).<a href="#section-1.1-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="terminology">
<section id="section-1.2">
        <h3 id="name-terminology">
<a href="#section-1.2" class="section-number selfRef">1.2. </a><a href="#name-terminology" class="section-name selfRef">Terminology</a>
        </h3>
<dl class="dlParallel dlCompact" id="section-1.2-1">
          <dt id="section-1.2-1.1">IdO</dt>
<dd style="margin-left: 4.0em" id="section-1.2-1.2">
  Identifier Owner, the owner of an identifier, e.g., a domain name, a
   telephone number, etc.<a href="#section-1.2-1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-1.2-1.3">STAR</dt>
<dd style="margin-left: 4.0em" id="section-1.2-1.4">
  Short-Term, Automatically Renewed X.509 certificates.<a href="#section-1.2-1.4" class="pilcrow">¶</a>
</dd>
</dl>
</section>
</div>
<div id="conventions-used-in-this-document">
<section id="section-1.3">
        <h3 id="name-conventions-used-in-this-do">
<a href="#section-1.3" class="section-number selfRef">1.3. </a><a href="#name-conventions-used-in-this-do" class="section-name selfRef">Conventions Used in This Document</a>
        </h3>
<p id="section-1.3-1">
    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="xref">RFC2119</a>]</span> <span>[<a href="#RFC8174" class="xref">RFC8174</a>]</span> 
    when, and only when, they appear in all capitals, as shown here.<a href="#section-1.3-1" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="protocol-flow">
<section id="section-2">
      <h2 id="name-protocol-flow">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-protocol-flow" class="section-name selfRef">Protocol Flow</a>
      </h2>
<p id="section-2-1">The following subsections describe the three main phases of the protocol:<a href="#section-2-1" class="pilcrow">¶</a></p>
<ul>
<li id="section-2-2.1">Bootstrap: the IdO asks an ACME CA to create a short-term,
 automatically renewed (STAR) certificate (<a href="#proto-bootstrap" class="xref">Section 2.1</a>);<a href="#section-2-2.1" class="pilcrow">¶</a>
</li>
<li id="section-2-2.2">Auto-renewal: the ACME CA periodically reissues the short-term
 certificate and posts it to the star-certificate URL (<a href="#proto-auto-renewal" class="xref">Section 2.2</a>);<a href="#section-2-2.2" class="pilcrow">¶</a>
</li>
<li id="section-2-2.3">Termination: the IdO requests the ACME CA to discontinue the
 automatic renewal of the certificate (<a href="#proto-termination" class="xref">Section 2.3</a>).<a href="#section-2-2.3" class="pilcrow">¶</a>
</li>
</ul>
<div id="proto-bootstrap">
<section id="section-2.1">
        <h3 id="name-bootstrap">
<a href="#section-2.1" class="section-number selfRef">2.1. </a><a href="#name-bootstrap" class="section-name selfRef">Bootstrap</a>
        </h3>
<p id="section-2.1-1">The IdO, in its role as an
ACME client, requests the CA to issue a STAR certificate, i.e., one that:<a href="#section-2.1-1" class="pilcrow">¶</a></p>
<ul>
<li id="section-2.1-2.1">Has a short validity, e.g., 24 to 72 hours. Note that the exact definition of "short" depends on the use case;<a href="#section-2.1-2.1" class="pilcrow">¶</a>
</li>
<li id="section-2.1-2.2">Is automatically renewed by the CA for a certain period of time;<a href="#section-2.1-2.2" class="pilcrow">¶</a>
</li>
<li id="section-2.1-2.3">Is downloadable from a (highly available) location.<a href="#section-2.1-2.3" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-2.1-3">Other than that, the ACME protocol flows as usual between IdO and CA.
In particular, IdO is responsible for satisfying the requested ACME challenges until the CA is willing to issue the requested certificate.
Per normal ACME processing, the IdO is given back an Order resource associated with the STAR certificate to be used in subsequent interaction with the CA (e.g., if
the certificate needs to be terminated.)<a href="#section-2.1-3" class="pilcrow">¶</a></p>
<p id="section-2.1-4">The bootstrap phase ends when the ACME CA updates the Order resource to include the URL for the issued STAR certificate.<a href="#section-2.1-4" class="pilcrow">¶</a></p>
</section>
</div>
<div id="proto-auto-renewal">
<section id="section-2.2">
        <h3 id="name-auto-renewal">
<a href="#section-2.2" class="section-number selfRef">2.2. </a><a href="#name-auto-renewal" class="section-name selfRef">Auto Renewal</a>
        </h3>
<p id="section-2.2-1">The CA issues the initial certificate after the authorization
        completes successfully.  It then automatically reissues the
        certificate using the same Certificate Signing Request (CSR) (and therefore the same identifier and
        public key) before the previous one expires and publishes it to the
        URL that was returned to the IdO at the end of the bootstrap phase.
        The certificate user, which could be either the IdO itself or a
        delegated third party as described in <span>[<a href="#I-D.ietf-acme-star-delegation" class="xref">STAR-DELEGATION</a>]</span>, obtains the
        certificate (<a href="#fetching-certificates" class="xref">Section 3.3</a>)
        and uses it.<a href="#section-2.2-1" class="pilcrow">¶</a></p>
<p id="section-2.2-2">The auto-renewal process (<a href="#figprotorefresh" class="xref">Figure 1</a>) goes on until either:<a href="#section-2.2-2" class="pilcrow">¶</a></p>
<ul>
<li id="section-2.2-3.1">IdO explicitly terminates the automatic renewal (<a href="#proto-termination" class="xref">Section 2.3</a>); or<a href="#section-2.2-3.1" class="pilcrow">¶</a>
</li>
<li id="section-2.2-3.2">Automatic renewal expires.<a href="#section-2.2-3.2" class="pilcrow">¶</a>
</li>
</ul>
<span id="name-auto-renewal-2"></span><div id="figprotorefresh">
<figure id="figure-1">
          <div class="artwork art-text alignLeft" id="section-2.2-4.1">
<pre>
   Certificate             ACME/STAR
   User                    Server
   |     Retrieve cert     |                     [...]
   |----------------------&gt;|                      |
   |                       +------.              /
   |                       |      |             /
   |                       | Automatic renewal :
   |                       |      |             \
   |                       |&lt;-----'              \
   |     Retrieve cert     |                      |
   |----------------------&gt;|            short validity period
   |                       |                      |
   |                       +------.              /
   |                       |      |             /
   |                       | Automatic renewal :
   |                       |      |             \
   |                       |&lt;-----'              \
   |     Retrieve cert     |                      |
   |----------------------&gt;|            short validity period
   |                       |                      |
   |                       +------.              /
   |                       |      |             /
   |                       | Automatic renewal :
   |                       |      |             \
   |                       |&lt;-----'              \
   |                       |                      |
   |         [...]         |                    [...]
</pre>
</div>
<figcaption><a href="#figure-1" class="selfRef">Figure 1</a>:
<a href="#name-auto-renewal-2" class="selfRef">Auto-renewal</a>
          </figcaption></figure>
</div>
</section>
</div>
<div id="proto-termination">
<section id="section-2.3">
        <h3 id="name-termination">
<a href="#section-2.3" class="section-number selfRef">2.3. </a><a href="#name-termination" class="section-name selfRef">Termination</a>
        </h3>
<p id="section-2.3-1">The IdO may request early termination of the STAR certificate by
        sending a cancellation request to the Order resource as described in
        <a href="#protocol-details-canceling" class="xref">Section 3.1.2</a>.  After
        the CA receives and verifies the request, it shall:<a href="#section-2.3-1" class="pilcrow">¶</a></p>
<ul>
<li id="section-2.3-2.1">Cancel the automatic renewal process for the STAR certificate;<a href="#section-2.3-2.1" class="pilcrow">¶</a>
</li>
<li id="section-2.3-2.2">Change the certificate publication resource to return an error indicating the termination of the issuance;<a href="#section-2.3-2.2" class="pilcrow">¶</a>
</li>
<li id="section-2.3-2.3">Change the status of the Order to "canceled".<a href="#section-2.3-2.3" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-2.3-3">Note that it is not necessary to explicitly revoke the short-term certificate.<a href="#section-2.3-3" class="pilcrow">¶</a></p>
<span id="name-termination-2"></span><div id="figprototerm">
<figure id="figure-2">
          <div class="artwork art-text alignLeft" id="section-2.3-4.1">
<pre>
   Certificate                                     ACME/STAR
   User                    IdO                     Server
   |                       |                       |
   |                       |      Cancel Order     |
   |                       +----------------------&gt;|
   |                       |                       +-------.
   |                       |                       |       |
   |                       |                       | End auto-renewal
   |                       |                       | Remove cert link
   |                       |                       | etc.
   |                       |                       |       |
   |                       |         Done          |&lt;------'
   |                       |&lt;----------------------+
   |                       |                       |
   |                                               |
   |              Retrieve cert                    |
   +----------------------------------------------&gt;|
   |              Error: autoRenewalCanceled       |
   |&lt;----------------------------------------------+
   |                                               |
</pre>
</div>
<figcaption><a href="#figure-2" class="selfRef">Figure 2</a>:
<a href="#name-termination-2" class="selfRef">Termination</a>
          </figcaption></figure>
</div>
</section>
</div>
</section>
</div>
<div id="protocol-details">
<section id="section-3">
      <h2 id="name-protocol-details">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-protocol-details" class="section-name selfRef">Protocol Details</a>
      </h2>
<p id="section-3-1">This section describes the protocol details, namely the extensions
to the ACME protocol required to issue STAR certificates.<a href="#section-3-1" class="pilcrow">¶</a></p>
<div id="acme-extensions">
<section id="section-3.1">
        <h3 id="name-acme-extensions">
<a href="#section-3.1" class="section-number selfRef">3.1. </a><a href="#name-acme-extensions" class="section-name selfRef">ACME Extensions</a>
        </h3>
<p id="section-3.1-1">This protocol extends the ACME protocol to allow for automatically renewed Orders.<a href="#section-3.1-1" class="pilcrow">¶</a></p>
<div id="star-order-ext">
<section id="section-3.1.1">
          <h4 id="name-extending-the-order-resourc">
<a href="#section-3.1.1" class="section-number selfRef">3.1.1. </a><a href="#name-extending-the-order-resourc" class="section-name selfRef">Extending the Order Resource</a>
          </h4>
<p id="section-3.1.1-1">The Order resource is extended with a new "auto-renewal" object
          that <span class="bcp14">MUST</span> be present for STAR certificates.  The
          "auto-renewal" object has the following structure:<a href="#section-3.1.1-1" class="pilcrow">¶</a></p>
<ul>
<li id="section-3.1.1-2.1">start-date (optional, string): The earliest date of validity
            of the first certificate issued, in <span>[<a href="#RFC3339" class="xref">RFC3339</a>]</span> format.  When omitted, the start date is as
            soon as authorization is complete.<a href="#section-3.1.1-2.1" class="pilcrow">¶</a>
</li>
<li id="section-3.1.1-2.2">end-date (required, string): The latest date of validity of
            the last certificate issued, in <span>[<a href="#RFC3339" class="xref">RFC3339</a>]</span> format.<a href="#section-3.1.1-2.2" class="pilcrow">¶</a>
</li>
<li id="section-3.1.1-2.3">lifetime (required, integer): The maximum validity period of
            each STAR certificate, an integer that denotes a number of
            seconds.  This is a nominal value that does not include any extra
            validity time due to server or client adjustment (see below).<a href="#section-3.1.1-2.3" class="pilcrow">¶</a>
</li>
<li id="section-3.1.1-2.4">lifetime-adjust (optional, integer): The amount of "left pad"
            added to each STAR certificate, an integer that denotes a number
            of seconds.  The default is 0.  If present, the value of the
            notBefore field that would otherwise appear in the STAR
            certificates is pre-dated by the specified number of seconds.  See
            <a href="#operational-cons-clocks" class="xref">Section 4.1</a> for
            why a client might want to use this control, and <a href="#computing-effective-cert-lifetime" class="xref">Section 3.5</a> for
            how the effective certificate lifetime is computed.  The value
            reflected by the server, together with the value of the lifetime
            attribute, can be used by the client as a hint to configure its
            polling timer.<a href="#section-3.1.1-2.4" class="pilcrow">¶</a>
</li>
<li id="section-3.1.1-2.5">allow-certificate-get (optional, boolean): See <a href="#certificate-get-nego" class="xref">Section 3.4</a>.<a href="#section-3.1.1-2.5" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-3.1.1-3">These attributes are included in a POST message when creating the
          Order as part of the object encoded as "payload".  They are returned
          when the Order has been created. The ACME server <span class="bcp14">MAY</span>
          adjust them at will according to its local policy (see also <a href="#capability-discovery" class="xref">Section 3.2</a>).<a href="#section-3.1.1-3" class="pilcrow">¶</a></p>
<p id="section-3.1.1-4">The optional notBefore and notAfter fields defined in <span><a href="https://www.rfc-editor.org/rfc/rfc8555#section-7.1.3" class="relref">Section 7.1.3</a> of [<a href="#RFC8555" class="xref">RFC8555</a>]</span> <span class="bcp14">MUST NOT</span> be present in a STAR Order.  If they are included, the
          server <span class="bcp14">MUST</span> return an error with status code 400 (Bad
          Request) and type "malformedRequest".<a href="#section-3.1.1-4" class="pilcrow">¶</a></p>
<p id="section-3.1.1-5"><span><a href="https://www.rfc-editor.org/rfc/rfc8555#section-7.1.6" class="relref">Section 7.1.6</a> of [<a href="#RFC8555" class="xref">RFC8555</a>]</span>
          defines the following values for the Order resource's status:
          "pending", "ready", "processing", "valid", and "invalid".  In the
          case of auto-renewal Orders, the status <span class="bcp14">MUST</span> be
          "valid" as long as STAR certificates are being issued.  This
          document adds a new status value: "canceled" (see <a href="#protocol-details-canceling" class="xref">Section 3.1.2</a>).<a href="#section-3.1.1-5" class="pilcrow">¶</a></p>
<p id="section-3.1.1-6">A STAR certificate is by definition a dynamic resource, i.e., it
          refers to an entity that varies over time.  Instead of overloading
          the semantics of the "certificate" attribute, this document defines
          a new attribute, "star-certificate", to be used instead of
          "certificate".<a href="#section-3.1.1-6" class="pilcrow">¶</a></p>
<ul>
<li id="section-3.1.1-7.1">star-certificate (optional, string): A URL for the (rolling)
            STAR certificate that has been issued in response to this
            Order.<a href="#section-3.1.1-7.1" class="pilcrow">¶</a>
</li>
</ul>
</section>
</div>
<div id="protocol-details-canceling">
<section id="section-3.1.2">
          <h4 id="name-canceling-an-auto-renewal-o">
<a href="#section-3.1.2" class="section-number selfRef">3.1.2. </a><a href="#name-canceling-an-auto-renewal-o" class="section-name selfRef">Canceling an Auto-renewal Order</a>
          </h4>
<p id="section-3.1.2-1">An important property of the auto-renewal Order is that it can be
          canceled by the IdO with no need for certificate revocation. To
          cancel the Order, the ACME client sends a POST to the Order URL as
          shown in <a href="#figcancelingstarorder" class="xref">Figure 3</a>.<a href="#section-3.1.2-1" class="pilcrow">¶</a></p>
<span id="name-canceling-an-auto-renewal-or"></span><div id="figcancelingstarorder">
<figure id="figure-3">
            <div id="section-3.1.2-2.1">
<pre class="sourcecode">
  POST /acme/order/ogfr8EcolOT HTTP/1.1
  Host: example.com
  Content-Type: application/jose+json

  {
    "protected": base64url({
      "alg": "ES256",
      "kid": "https://example.com/acme/acct/gw06UNhKfOve",
      "nonce": "Alc00Ap6Rt7GMkEl3L1JX5",
      "url": "https://example.com/acme/order/ogfr8EcolOT"
    }),
    "payload": base64url({
      "status": "canceled"
    }),
    "signature": "g454e3hdBlkT4AEw...nKePnUyZTjGtXZ6H"
  }
</pre>
</div>
<figcaption><a href="#figure-3" class="selfRef">Figure 3</a>:
<a href="#name-canceling-an-auto-renewal-or" class="selfRef">Canceling an Auto-renewal Order</a>
            </figcaption></figure>
</div>
<p id="section-3.1.2-3">After a successful cancellation, the server <span class="bcp14">MUST NOT</span> issue any additional certificates for this Order.<a href="#section-3.1.2-3" class="pilcrow">¶</a></p>
<p id="section-3.1.2-4">When the Order is canceled, the server:<a href="#section-3.1.2-4" class="pilcrow">¶</a></p>
<ul>
<li id="section-3.1.2-5.1">
              <span class="bcp14">MUST</span> update the status of the Order resource to "canceled" and <span class="bcp14">MUST</span> set an appropriate "expires" date;<a href="#section-3.1.2-5.1" class="pilcrow">¶</a>
</li>
<li id="section-3.1.2-5.2">
              <span class="bcp14">MUST</span> respond with 403 (Forbidden) to any
            requests to the star-certificate endpoint.  The response
            <span class="bcp14">SHOULD</span> provide additional information using a
            problem document <span>[<a href="#RFC7807" class="xref">RFC7807</a>]</span> with
            type "urn:ietf:params:acme:error:autoRenewalCanceled".<a href="#section-3.1.2-5.2" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-3.1.2-6">Issuing a cancellation for an Order that is not in "valid" state
          is not allowed.  A client <span class="bcp14">MUST NOT</span> send such a
          request, and a server <span class="bcp14">MUST</span> return an error response
          with status code 400 (Bad Request) and type
          "urn:ietf:params:acme:error:autoRenewalCancellationInvalid".<a href="#section-3.1.2-6" class="pilcrow">¶</a></p>
<p id="section-3.1.2-7">The state machine described in <span><a href="https://www.rfc-editor.org/rfc/rfc8555#section-7.1.6" class="relref">Section 7.1.6</a> of [<a href="#RFC8555" class="xref">RFC8555</a>]</span> is extended as illustrated in
          <a href="#fig-order-state-transitions-ext" class="xref">Figure 4</a>.<a href="#section-3.1.2-7" class="pilcrow">¶</a></p>
<span id="name-state-transitions-for-star-"></span><div id="fig-order-state-transitions-ext">
<figure id="figure-4">
            <div class="artwork art-text alignLeft" id="section-3.1.2-8.1">
<pre>
    pending --------------+
       |                  |
       | All authz        |
       | "valid"          |
       V                  |
     ready ---------------+
       |                  |
       | Receive          |
       | finalize         |
       | request          |
       V                  |
   processing ------------+
       |                  |
       | First            |
       | certificate      | Error or
       | issued           | Authorization failure
       |                  |
       |                  V
       |               invalid
       V
     valid----------------+
       |                  |
       | STAR             |
       | Certificate      | Natural
       | canceled         | Expiration
       V                  |
    canceled             ='=
</pre>
</div>
<figcaption><a href="#figure-4" class="selfRef">Figure 4</a>:
<a href="#name-state-transitions-for-star-" class="selfRef">State Transitions for STAR Order Objects</a>
            </figcaption></figure>
</div>
<p id="section-3.1.2-9">Explicit certificate revocation using the revokeCert interface
          (<span><a href="https://www.rfc-editor.org/rfc/rfc8555#section-7.6" class="relref">Section 7.6</a> of [<a href="#RFC8555" class="xref">RFC8555</a>]</span>) is not
          supported for STAR certificates.  A server receiving a revocation
          request for a STAR certificate <span class="bcp14">MUST</span> return an error
          response with status code 403 (Forbidden) and type
          "urn:ietf:params:acme:error:autoRenewalRevocationNotSupported".<a href="#section-3.1.2-9" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="capability-discovery">
<section id="section-3.2">
        <h3 id="name-capability-discovery">
<a href="#section-3.2" class="section-number selfRef">3.2. </a><a href="#name-capability-discovery" class="section-name selfRef">Capability Discovery</a>
        </h3>
<p id="section-3.2-1">In order to support the discovery of STAR capabilities, the "meta"
        field inside the directory object defined in <span><a href="https://www.rfc-editor.org/rfc/rfc8555#section-9.7.6" class="relref">Section 9.7.6</a> of [<a href="#RFC8555" class="xref">RFC8555</a>]</span> is extended with a new
        "auto-renewal" object.  The "auto-renewal" object <span class="bcp14">MUST</span>
        be present if the server supports STAR.  Its structure is as
        follows:<a href="#section-3.2-1" class="pilcrow">¶</a></p>
<ul>
<li id="section-3.2-2.1">min-lifetime (required, integer): Minimum acceptable value for
          auto-renewal lifetime, in seconds.<a href="#section-3.2-2.1" class="pilcrow">¶</a>
</li>
<li id="section-3.2-2.2">max-duration (required, integer): Maximum allowed delta between
          the end-date and start-date attributes of the Order's auto-renewal
   object.<a href="#section-3.2-2.2" class="pilcrow">¶</a>
</li>
<li id="section-3.2-2.3">allow-certificate-get (optional, boolean): See <a href="#certificate-get-nego" class="xref">Section 3.4</a>.<a href="#section-3.2-2.3" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-3.2-3">An example directory object advertising STAR support with one-day
        min-lifetime and one-year max-duration and supporting certificate
        fetching with an HTTP GET is shown in <a href="#figstardir" class="xref">Figure 5</a>.<a href="#section-3.2-3" class="pilcrow">¶</a></p>
<span id="name-directory-object-with-star-"></span><div id="figstardir">
<figure id="figure-5">
          <div id="section-3.2-4.1">
<pre class="sourcecode lang-JSON">
 {
    "new-nonce": "https://example.com/acme/new-nonce",
    "new-account": "https://example.com/acme/new-account",
    "new-order": "https://example.com/acme/new-order",
    "new-authz": "https://example.com/acme/new-authz",
    "revoke-cert": "https://example.com/acme/revoke-cert",
    "key-change": "https://example.com/acme/key-change",
    "meta": {
      "terms-of-service": "https://example.com/acme/terms/2017-5-30",
      "website": "https://www.example.com/",
      "caa-identities": ["example.com"],
      "auto-renewal": {
        "min-lifetime": 86400,
        "max-duration":  31536000,
        "allow-certificate-get": true
      }
    }
 }
</pre>
</div>
<figcaption><a href="#figure-5" class="selfRef">Figure 5</a>:
<a href="#name-directory-object-with-star-" class="selfRef">Directory Object with STAR Support</a>
          </figcaption></figure>
</div>
</section>
</div>
<div id="fetching-certificates">
<section id="section-3.3">
        <h3 id="name-fetching-the-certificates">
<a href="#section-3.3" class="section-number selfRef">3.3. </a><a href="#name-fetching-the-certificates" class="section-name selfRef">Fetching the Certificates</a>
        </h3>
<p id="section-3.3-1">The certificate is fetched from the star-certificate endpoint with
        POST-as-GET as per <span><a href="https://www.rfc-editor.org/rfc/rfc8555#section-7.4.2" class="relref">Section 7.4.2</a> of [<a href="#RFC8555" class="xref">RFC8555</a>]</span> unless the client and server have successfully
        negotiated the "unauthenticated GET" option described in <a href="#certificate-get-nego" class="xref">Section 3.4</a>.  In such case, the
        client can simply issue a GET to the star-certificate resource without
        authenticating itself to the server as illustrated in <a href="#figunauthgetstarcert" class="xref">Figure 6</a>.<a href="#section-3.3-1" class="pilcrow">¶</a></p>
<span id="name-fetching-a-star-certificate"></span><div id="figunauthgetstarcert">
<figure id="figure-6">
          <div class="artwork art-text alignLeft" id="section-3.3-2.1">
<pre>
  GET /acme/cert/g7m3ZQeTEqa HTTP/1.1
  Host: example.com
  Accept: application/pem-certificate-chain

  HTTP/1.1 200 OK
  Content-Type: application/pem-certificate-chain
  Link: &lt;https://example.com/acme/some-directory&gt;;rel="index"
  Cert-Not-Before: Thu, 3 Oct 2019 00:00:00 GMT
  Cert-Not-After: Thu, 10 Oct 2019 00:00:00 GMT

  -----BEGIN CERTIFICATE-----
  [End-entity certificate contents]
  -----END CERTIFICATE-----
  -----BEGIN CERTIFICATE-----
  [Issuer certificate contents]
  -----END CERTIFICATE-----
  -----BEGIN CERTIFICATE-----
  [Other certificate contents]
  -----END CERTIFICATE-----
</pre>
</div>
<figcaption><a href="#figure-6" class="selfRef">Figure 6</a>:
<a href="#name-fetching-a-star-certificate" class="selfRef">Fetching a STAR Certificate with Unauthenticated GET</a>
          </figcaption></figure>
</div>
<p id="section-3.3-3">The server <span class="bcp14">SHOULD</span> include the "Cert-Not-Before" and
        "Cert-Not-After" HTTP header fields in the response.  When they exist,
        they <span class="bcp14">MUST</span> be equal to the respective fields inside the
        end-entity certificate. Their format is "HTTP-date" as defined in
        <span><a href="https://www.rfc-editor.org/rfc/rfc7231#section-7.1.1.2" class="relref">Section 7.1.1.2</a> of [<a href="#RFC7231" class="xref">RFC7231</a>]</span>.  Their
        purpose is to enable client implementations that do not parse the
        certificate.<a href="#section-3.3-3" class="pilcrow">¶</a></p>
<p id="section-3.3-4">The following are further clarifications regarding usage of these
        header fields as per <span><a href="https://www.rfc-editor.org/rfc/rfc7231#section-8.3.1" class="relref">Section 8.3.1</a> of [<a href="#RFC7231" class="xref">RFC7231</a>]</span>. All apply to both headers.<a href="#section-3.3-4" class="pilcrow">¶</a></p>
<ul>
<li id="section-3.3-5.1">This header field is a single value, not a list.<a href="#section-3.3-5.1" class="pilcrow">¶</a>
</li>
<li id="section-3.3-5.2">The header field is used only in responses to GET, HEAD, and
          POST-as-GET requests, and only for MIME types that denote public key
          certificates.<a href="#section-3.3-5.2" class="pilcrow">¶</a>
</li>
<li id="section-3.3-5.3">Header field semantics are independent of context.<a href="#section-3.3-5.3" class="pilcrow">¶</a>
</li>
<li id="section-3.3-5.4">The header field is not hop-by-hop.<a href="#section-3.3-5.4" class="pilcrow">¶</a>
</li>
<li id="section-3.3-5.5">Intermediaries <span class="bcp14">MAY</span> insert or delete the value;<a href="#section-3.3-5.5" class="pilcrow">¶</a>
</li>
<li id="section-3.3-5.6">If an intermediary inserts the value, it <span class="bcp14">MUST</span>
          ensure that the newly added value matches the corresponding value in
          the certificate.<a href="#section-3.3-5.6" class="pilcrow">¶</a>
</li>
<li id="section-3.3-5.7">The header field is not appropriate for a Vary field.<a href="#section-3.3-5.7" class="pilcrow">¶</a>
</li>
<li id="section-3.3-5.8">The header field is allowed within message trailers.<a href="#section-3.3-5.8" class="pilcrow">¶</a>
</li>
<li id="section-3.3-5.9">The header field is not appropriate within redirects.<a href="#section-3.3-5.9" class="pilcrow">¶</a>
</li>
<li id="section-3.3-5.10">The header field does not introduce additional security
          considerations. It discloses in a simpler form information that is
   already available inside the certificate.<a href="#section-3.3-5.10" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-3.3-6">To improve robustness, the next certificate <span class="bcp14">MUST</span> be made
available by the ACME CA at the URL indicated by "star-certificate" halfway
through the lifetime of the currently active certificate at the latest.  It is
worth noting that this has an implication in case of cancellation; in fact,
from the time the next certificate is made available, the cancellation is not
completely effective until the "next" certificate also expires.  To avoid the
client accidentally entering a broken state, the notBefore of the "next"
certificate <span class="bcp14">MUST</span> be set so that the certificate is already
valid when it is published at the "star-certificate" URL.  Note that the
server might need to increase the auto-renewal lifetime-adjust value to
satisfy the latter requirement.  For a detailed description of the renewal
scheduling logic, see <a href="#computing-effective-cert-lifetime" class="xref">Section 3.5</a>.  For further rationale on the need for adjusting the
certificate validity, see <a href="#operational-cons-clocks" class="xref">Section 4.1</a>.<a href="#section-3.3-6" class="pilcrow">¶</a></p>
<p id="section-3.3-7">The server <span class="bcp14">MUST NOT</span> issue any certificates for this
        Order with notAfter after the auto-renewal end-date.<a href="#section-3.3-7" class="pilcrow">¶</a></p>
<p id="section-3.3-8">For expired Orders, the server <span class="bcp14">MUST</span> respond with 403
        (Forbidden) to any requests to the star-certificate endpoint.  The
        response <span class="bcp14">SHOULD</span> provide additional information using a
        problem document <span>[<a href="#RFC7807" class="xref">RFC7807</a>]</span> with type
        "urn:ietf:params:acme:error:autoRenewalExpired". Note that the Order
        resource's state remains "valid", as per the base protocol.<a href="#section-3.3-8" class="pilcrow">¶</a></p>
</section>
</div>
<div id="certificate-get-nego">
<section id="section-3.4">
        <h3 id="name-negotiating-an-unauthentica">
<a href="#section-3.4" class="section-number selfRef">3.4. </a><a href="#name-negotiating-an-unauthentica" class="section-name selfRef">Negotiating an Unauthenticated GET</a>
        </h3>
<p id="section-3.4-1">In order to enable the name delegation workflow defined in <span>[<a href="#I-D.ietf-acme-star-delegation" class="xref">STAR-DELEGATION</a>]</span> and to
        increase the reliability of the STAR ecosystem (see <a href="#dependability" class="xref">Section 4.3</a> for details), this document
        defines a mechanism that allows a server to advertise support for
        accessing star-certificate resources via unauthenticated GET (in
        addition to POST-as-GET), and a client to enable this service with
        per-Order granularity.<a href="#section-3.4-1" class="pilcrow">¶</a></p>
<p id="section-3.4-2">Specifically, a server states its availability to grant
        unauthenticated access to a client's Order star-certificate by setting
        the allow-certificate-get attribute to "true" in the auto-renewal object
        of the meta field inside the directory object:<a href="#section-3.4-2" class="pilcrow">¶</a></p>
<ul>
<li id="section-3.4-3.1">allow-certificate-get (optional, boolean): If this field is
          present and set to "true", the server allows GET (and HEAD) requests
          to star-certificate URLs.<a href="#section-3.4-3.1" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-3.4-4">A client states its desire to access the issued star-certificate
        via unauthenticated GET by adding an allow-certificate-get attribute
        to the auto-renewal object of the payload of its newOrder request and
        setting it to "true".<a href="#section-3.4-4" class="pilcrow">¶</a></p>
<ul>
<li id="section-3.4-5.1">allow-certificate-get (optional, boolean): If this field is
          present and set to "true", the client requests the server to allow
          unauthenticated GET (and HEAD) to the star-certificate associated
          with this Order.<a href="#section-3.4-5.1" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-3.4-6">If the server accepts the request, it <span class="bcp14">MUST</span> reflect
        the attribute setting in the resulting order object.<a href="#section-3.4-6" class="pilcrow">¶</a></p>
<p id="section-3.4-7">Note that even when the use of unauthenticated GET has been agreed
        upon, the server <span class="bcp14">MUST</span> also allow POST-as-GET requests
        to the star-certificate resource.<a href="#section-3.4-7" class="pilcrow">¶</a></p>
</section>
</div>
<div id="computing-effective-cert-lifetime">
<section id="section-3.5">
        <h3 id="name-computing-notbefore-and-not">
<a href="#section-3.5" class="section-number selfRef">3.5. </a><a href="#name-computing-notbefore-and-not" class="section-name selfRef">Computing notBefore and notAfter of STAR Certificates</a>
        </h3>
<p id="section-3.5-1">We define "nominal renewal date" as the point in time when a new
        short-term certificate for a given STAR Order is due.  Its cadence is
        a multiple of the Order's auto-renewal lifetime that starts with the
        issuance of the first short-term certificate and is upper-bounded by
        the Order's auto-renewal end-date (<a href="#fignrd" class="xref">Figure 7</a>).<a href="#section-3.5-1" class="pilcrow">¶</a></p>
<span id="name-nominal-renewal-date"></span><div id="fignrd">
<figure id="figure-7">
          <div class="artwork art-text alignLeft" id="section-3.5-2.1">
<pre>
    T      - STAR Order's auto-renewal lifetime
    end    - STAR Order's auto-renewal end-date
    nrd[i] - nominal renewal date of the i-th STAR certificate


                 .- T -.   .- T -.   .- T -.   .__.
                /       \ /       \ /       \ /  end
    -----------o---------o---------o---------o----X-------&gt; t
              nrd[0]    nrd[1]    nrd[2]    nrd[3]
</pre>
</div>
<figcaption><a href="#figure-7" class="selfRef">Figure 7</a>:
<a href="#name-nominal-renewal-date" class="selfRef">Nominal Renewal Date</a>
          </figcaption></figure>
</div>
<p id="section-3.5-3">The rules to determine the notBefore and notAfter values of the i-th STAR
certificate are as follows:<a href="#section-3.5-3" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-3.5-4">
<pre>
    notAfter  = min(nrd[i] + T, end)
    notBefore = nrd[i] - max(adjust_client, adjust_server)
</pre><a href="#section-3.5-4" class="pilcrow">¶</a>
</div>
<p id="section-3.5-5">Where "adjust_client" is the minimum value between the auto-renewal
        lifetime-adjust value ("la"), optionally supplied by the client, and
        the auto-renewal lifetime of each short-term certificate ("T");
        "adjust_server" is the amount of padding added by the ACME server to
        make sure that all certificates being published are valid at the time
        of publication.  The server padding is a fraction (f) of T (i.e., f
        * T with .5 &lt;= f &lt; 1; see <a href="#fetching-certificates" class="xref">Section 3.3</a>):<a href="#section-3.5-5" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-3.5-6">
<pre>
    adjust_client = min(T, la)
    adjust_server = f * T
</pre><a href="#section-3.5-6" class="pilcrow">¶</a>
</div>
<p id="section-3.5-7">Note that the ACME server <span class="bcp14">MUST NOT</span> set the notBefore of the first STAR
certificate to a date prior to the auto-renewal start-date.<a href="#section-3.5-7" class="pilcrow">¶</a></p>
<div id="example">
<section id="section-3.5.1">
          <h4 id="name-example">
<a href="#section-3.5.1" class="section-number selfRef">3.5.1. </a><a href="#name-example" class="section-name selfRef">Example</a>
          </h4>
<p id="section-3.5.1-1">Given a server that intends to publish the next STAR certificate halfway
through the lifetime of the previous one, and a STAR Order with the following
attributes:<a href="#section-3.5.1-1" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-3.5.1-2">
<pre>
     "auto-renewal": {
       "start-date": "2019-01-10T00:00:00Z",
       "end-date": "2019-01-20T00:00:00Z",
       "lifetime": 345600,          // 4 days
       "lifetime-adjust": 259200    // 3 days
     }
</pre><a href="#section-3.5.1-2" class="pilcrow">¶</a>
</div>
<p id="section-3.5.1-3">The amount of time that needs to be subtracted from each nominal renewal
date is 3 days, i.e., max(min(345600, 259200), 345600 * .5).<a href="#section-3.5.1-3" class="pilcrow">¶</a></p>
<p id="section-3.5.1-4">The notBefore and notAfter of each short-term certificate are:<a href="#section-3.5.1-4" class="pilcrow">¶</a></p>
<table class="center" id="table-1">
            <caption><a href="#table-1" class="selfRef">Table 1</a></caption>
<thead>
              <tr>
                <th class="text-left" rowspan="1" colspan="1">notBefore</th>
                <th class="text-left" rowspan="1" colspan="1">notAfter</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td class="text-left" rowspan="1" colspan="1">2019-01-10T00:00:00Z</td>
                <td class="text-left" rowspan="1" colspan="1">2019-01-14T00:00:00Z</td>
              </tr>
              <tr>
                <td class="text-left" rowspan="1" colspan="1">2019-01-11T00:00:00Z</td>
                <td class="text-left" rowspan="1" colspan="1">2019-01-18T00:00:00Z</td>
              </tr>
              <tr>
                <td class="text-left" rowspan="1" colspan="1">2019-01-15T00:00:00Z</td>
                <td class="text-left" rowspan="1" colspan="1">2019-01-20T00:00:00Z</td>
              </tr>
            </tbody>
          </table>
<p id="section-3.5.1-6">The value of the notBefore is also the time at which the client should expect
the new certificate to be available from the star-certificate endpoint.<a href="#section-3.5.1-6" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
</section>
</div>
<div id="operational-considerations">
<section id="section-4">
      <h2 id="name-operational-considerations">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-operational-considerations" class="section-name selfRef">Operational Considerations</a>
      </h2>
<div id="operational-cons-clocks">
<section id="section-4.1">
        <h3 id="name-the-meaning-of-short-term-a">
<a href="#section-4.1" class="section-number selfRef">4.1. </a><a href="#name-the-meaning-of-short-term-a" class="section-name selfRef">The Meaning of "Short Term" and the Impact of Skewed Clocks</a>
        </h3>
<p id="section-4.1-1">"Short Term" is a relative concept; therefore, trying to define a
        cutoff point that works in all cases would be a useless exercise.  In
        practice, the expected lifetime of a STAR certificate will be counted
        in minutes, hours, or days, depending on different factors: the
        underlying requirements for revocation, how much clock synchronization
        is expected among relying parties and the issuing CA, etc.<a href="#section-4.1-1" class="pilcrow">¶</a></p>
<p id="section-4.1-2">Nevertheless, this section attempts to provide reasonable
        suggestions for the Web use case, informed by current operational and
        research experience.<a href="#section-4.1-2" class="pilcrow">¶</a></p>
<p id="section-4.1-3">Acer et al. <span>[<a href="#ACER" class="xref">ACER</a>]</span> find that one of
        the main causes of "HTTPS error" warnings in browsers is misconfigured
        client clocks.  In particular, they observe that roughly 95% of the
        "severe" clock skews -- the 6.7% of clock-related breakage reports
        that account for clients that are more than 24 hours behind -- happen
        to be within 6-7 days.<a href="#section-4.1-3" class="pilcrow">¶</a></p>
<p id="section-4.1-4">In order to avoid these spurious warnings about a not yet valid
        server certificate, site owners could use the auto-renewal
        lifetime-adjust attribute to control the effective lifetime of their
        Web-facing certificates.  The exact number depends on the percentage
        of the "clock-skewed" population that the site owner expects to
        protect -- 5 days cover 97.3%, 7 days cover 99.6% -- as well as the
        nominal auto-renewal lifetime of the STAR Order.  Note that exact
        choice is also likely to depend on the kinds of client that are
        prevalent for a given site or app -- for example, Android and Mac OS
        clients are known to behave better than Windows clients.  These
        considerations are clearly out of scope of this document.<a href="#section-4.1-4" class="pilcrow">¶</a></p>
<p id="section-4.1-5">In terms of security, STAR certificates and certificates with the
        Online Certificate Status Protocol (OCSP) "must-staple" flag asserted <span>[<a href="#RFC7633" class="xref">RFC7633</a>]</span> can be considered roughly
        equivalent if the STAR certificate's and the OCSP response's lifetimes
        are the same. (Here, "must-staple" refers to a certificate carrying a
 TLS feature extension with the "status_request" extension identifier
 <span>[<a href="#RFC6066" class="xref">RFC6066</a>]</span>.)  Given OCSP responses can be cached, on average, for 4
        days <span>[<a href="#STARK" class="xref">STARK</a>]</span>, it is
        <span class="bcp14">RECOMMENDED</span> that a STAR certificate that is used on the
        Web has an "effective" lifetime (excluding any adjustment to account
        for clock skews) no longer than 4 days.<a href="#section-4.1-5" class="pilcrow">¶</a></p>
</section>
</div>
<div id="impact-on-certificate-transparency-ct-logs">
<section id="section-4.2">
        <h3 id="name-impact-on-certificate-trans">
<a href="#section-4.2" class="section-number selfRef">4.2. </a><a href="#name-impact-on-certificate-trans" class="section-name selfRef">Impact on Certificate Transparency (CT) Logs</a>
        </h3>
<p id="section-4.2-1">Even in the highly unlikely case STAR becomes the only certificate
        issuance model, discussion with the IETF TRANS Working Group and
        implementers of Certificate Transparency (CT) logs suggests that existing
        CT Log server implementations are capable of sustaining the resulting
        100-fold increase in ingestion rate. Additionally, such a future
        higher load could be managed with a variety of techniques (e.g.,
        sharding by modulo of certificate hash, using "smart" load-balancing
        CT proxies, etc.). With regards to the increase in the log size,
        current CT log growth is already being managed with schemes like
        Chrome's Log Policy <span>[<a href="#OBRIEN" class="xref">OBRIEN</a>]</span>, which
        allow Operators to define their log life cycle, as well as allowing the CAs,
        User Agents, Monitors, and any other interested entities to build in
        support for that life cycle ahead of time.<a href="#section-4.2-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="dependability">
<section id="section-4.3">
        <h3 id="name-http-caching-and-dependabil">
<a href="#section-4.3" class="section-number selfRef">4.3. </a><a href="#name-http-caching-and-dependabil" class="section-name selfRef">HTTP Caching and Dependability</a>
        </h3>
<p id="section-4.3-1">When using authenticated POST-as-GET, the HTTPS endpoint from where
        the STAR certificate is fetched can't be easily replicated by an
        on-path HTTP cache.  Reducing the caching properties of the protocol
        makes STAR clients increasingly dependent on the ACME server
        availability.  This might be problematic given the relatively high
        rate of client-server interactions in a STAR ecosystem, especially
        when multiple endpoints (e.g., a high number of CDN edge nodes) end up
        requesting the same certificate.  Clients and servers should consider
        using the mechanism described in <a href="#certificate-get-nego" class="xref">Section 3.4</a> to mitigate the risk.<a href="#section-4.3-1" class="pilcrow">¶</a></p>
<p id="section-4.3-2">When using unauthenticated GET to fetch the STAR certificate, the server <span class="bcp14">SHALL</span>
use the appropriate cache directives to set the freshness lifetime of the
response (<span><a href="https://www.rfc-editor.org/rfc/rfc7234#section-5.2" class="relref">Section 5.2</a> of [<a href="#RFC7234" class="xref">RFC7234</a>]</span>) such that on-path caches will consider
it stale before or at the time its effective lifetime is due to expire.<a href="#section-4.3-2" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="iana-considerations">
<section id="section-5">
      <h2 id="name-iana-considerations">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<div id="new-registries">
<section id="section-5.1">
        <h3 id="name-new-registries">
<a href="#section-5.1" class="section-number selfRef">5.1. </a><a href="#name-new-registries" class="section-name selfRef">New Registries</a>
        </h3>
<p id="section-5.1-1">Per this document, IANA has created the following new registries:<a href="#section-5.1-1" class="pilcrow">¶</a></p>
<ul>
<li id="section-5.1-2.1">ACME Order Auto-Renewal Fields (<a href="#iana-order-auto-renewal-registry" class="xref">Section 5.4</a>)<a href="#section-5.1-2.1" class="pilcrow">¶</a>
</li>
<li id="section-5.1-2.2">ACME Directory Metadata Auto-Renewal Fields (<a href="#iana-metadata-auto-renewal-registry" class="xref">Section 5.6</a>)<a href="#section-5.1-2.2" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-5.1-3">These registries are administered under a Specification Required policy
<span>[<a href="#RFC8126" class="xref">RFC8126</a>]</span>.<a href="#section-5.1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="new-error-types">
<section id="section-5.2">
        <h3 id="name-new-error-types">
<a href="#section-5.2" class="section-number selfRef">5.2. </a><a href="#name-new-error-types" class="section-name selfRef">New Error Types</a>
        </h3>
<p id="section-5.2-1">Per this document, IANA has added the following entries to the "ACME Error Types" registry:<a href="#section-5.2-1" class="pilcrow">¶</a></p>
<table class="center" id="table-2">
          <caption><a href="#table-2" class="selfRef">Table 2</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Type</th>
              <th class="text-left" rowspan="1" colspan="1">Description</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">autoRenewalCanceled</td>
              <td class="text-left" rowspan="1" colspan="1">The short-term certificate is no longer available because the auto-renewal Order has been explicitly canceled by the IdO</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">autoRenewalExpired</td>
              <td class="text-left" rowspan="1" colspan="1">The short-term certificate is no longer available because the auto-renewal Order has expired</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">autoRenewalCancellationInvalid</td>
              <td class="text-left" rowspan="1" colspan="1">A request to cancel an auto-renewal Order that is not in state "valid" has been received</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">autoRenewalRevocationNotSupported</td>
              <td class="text-left" rowspan="1" colspan="1">A request to revoke an auto-renewal Order has been received</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
<div id="new-fields-in-order-objects">
<section id="section-5.3">
        <h3 id="name-new-fields-in-order-objects">
<a href="#section-5.3" class="section-number selfRef">5.3. </a><a href="#name-new-fields-in-order-objects" class="section-name selfRef">New Fields in Order Objects</a>
        </h3>
<p id="section-5.3-1">Per this document, IANA has added the following entries to the
        "ACME Order Object Fields" registry:<a href="#section-5.3-1" class="pilcrow">¶</a></p>
<table class="center" id="table-3">
          <caption><a href="#table-3" class="selfRef">Table 3</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Field Name</th>
              <th class="text-left" rowspan="1" colspan="1">Field Type</th>
              <th class="text-left" rowspan="1" colspan="1">Configurable</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">auto-renewal</td>
              <td class="text-left" rowspan="1" colspan="1">object</td>
              <td class="text-left" rowspan="1" colspan="1">true</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">star-certificate</td>
              <td class="text-left" rowspan="1" colspan="1">string</td>
              <td class="text-left" rowspan="1" colspan="1">false</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
<div id="iana-order-auto-renewal-registry">
<section id="section-5.4">
        <h3 id="name-fields-in-the-auto-renewal-">
<a href="#section-5.4" class="section-number selfRef">5.4. </a><a href="#name-fields-in-the-auto-renewal-" class="section-name selfRef">Fields in the "auto-renewal" Object within an Order Object</a>
        </h3>
<p id="section-5.4-1">The "ACME Order Auto-Renewal Fields" registry lists field names that are
defined for use in the JSON object included in the "auto-renewal" field of an
ACME order object.<a href="#section-5.4-1" class="pilcrow">¶</a></p>
<p id="section-5.4-2">Template:<a href="#section-5.4-2" class="pilcrow">¶</a></p>
<ul>
<li id="section-5.4-3.1">Field name: The string to be used as a field name in the JSON object<a href="#section-5.4-3.1" class="pilcrow">¶</a>
</li>
<li id="section-5.4-3.2">Field type: The type of value to be provided, e.g., string, boolean, array of
string<a href="#section-5.4-3.2" class="pilcrow">¶</a>
</li>
<li id="section-5.4-3.3">Configurable: Boolean indicating whether the server should accept values
provided by the client<a href="#section-5.4-3.3" class="pilcrow">¶</a>
</li>
<li id="section-5.4-3.4">Reference: Where this field is defined<a href="#section-5.4-3.4" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-5.4-4">Initial contents: The fields and descriptions defined in <a href="#star-order-ext" class="xref">Section 3.1.1</a>.<a href="#section-5.4-4" class="pilcrow">¶</a></p>
<table class="center" id="table-4">
          <caption><a href="#table-4" class="selfRef">Table 4</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Field Name</th>
              <th class="text-left" rowspan="1" colspan="1">Field Type</th>
              <th class="text-left" rowspan="1" colspan="1">Configurable</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">start-date</td>
              <td class="text-left" rowspan="1" colspan="1">string</td>
              <td class="text-left" rowspan="1" colspan="1">true</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">end-date</td>
              <td class="text-left" rowspan="1" colspan="1">string</td>
              <td class="text-left" rowspan="1" colspan="1">true</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">lifetime</td>
              <td class="text-left" rowspan="1" colspan="1">integer</td>
              <td class="text-left" rowspan="1" colspan="1">true</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">lifetime-adjust</td>
              <td class="text-left" rowspan="1" colspan="1">integer</td>
              <td class="text-left" rowspan="1" colspan="1">true</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">allow-certificate-get</td>
              <td class="text-left" rowspan="1" colspan="1">boolean</td>
              <td class="text-left" rowspan="1" colspan="1">true</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
<div id="new-fields-in-the-meta-object-within-a-directory-object">
<section id="section-5.5">
        <h3 id="name-new-fields-in-the-meta-obje">
<a href="#section-5.5" class="section-number selfRef">5.5. </a><a href="#name-new-fields-in-the-meta-obje" class="section-name selfRef">New Fields in the "meta" Object within a Directory Object</a>
        </h3>
<p id="section-5.5-1">Per this document, IANA has added the following entry to the "ACME Directory Metadata Fields":<a href="#section-5.5-1" class="pilcrow">¶</a></p>
<table class="center" id="table-5">
          <caption><a href="#table-5" class="selfRef">Table 5</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Field Name</th>
              <th class="text-left" rowspan="1" colspan="1">Field Type</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">auto-renewal</td>
              <td class="text-left" rowspan="1" colspan="1">object</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
<div id="iana-metadata-auto-renewal-registry">
<section id="section-5.6">
        <h3 id="name-fields-in-the-auto-renewal-o">
<a href="#section-5.6" class="section-number selfRef">5.6. </a><a href="#name-fields-in-the-auto-renewal-o" class="section-name selfRef">Fields in the "auto-renewal" Object within a Directory Metadata Object</a>
        </h3>
<p id="section-5.6-1">The "ACME Directory Metadata Auto-Renewal Fields" registry lists field names
that are defined for use in the JSON object included in the "auto-renewal"
field of an ACME directory "meta" object.<a href="#section-5.6-1" class="pilcrow">¶</a></p>
<p id="section-5.6-2">Template:<a href="#section-5.6-2" class="pilcrow">¶</a></p>
<ul>
<li id="section-5.6-3.1">Field name: The string to be used as a field name in the JSON object<a href="#section-5.6-3.1" class="pilcrow">¶</a>
</li>
<li id="section-5.6-3.2">Field type: The type of value to be provided, e.g., string, boolean, array of
string<a href="#section-5.6-3.2" class="pilcrow">¶</a>
</li>
<li id="section-5.6-3.3">Reference: Where this field is defined<a href="#section-5.6-3.3" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-5.6-4">Initial contents: The fields and descriptions defined in <a href="#capability-discovery" class="xref">Section 3.2</a>.<a href="#section-5.6-4" class="pilcrow">¶</a></p>
<table class="center" id="table-6">
          <caption><a href="#table-6" class="selfRef">Table 6</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Field Name</th>
              <th class="text-left" rowspan="1" colspan="1">Field Type</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">min-lifetime</td>
              <td class="text-left" rowspan="1" colspan="1">integer</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">max-duration</td>
              <td class="text-left" rowspan="1" colspan="1">integer</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">allow-certificate-get</td>
              <td class="text-left" rowspan="1" colspan="1">boolean</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
<div id="iana-http-headers">
<section id="section-5.7">
        <h3 id="name-cert-not-before-and-cert-no">
<a href="#section-5.7" class="section-number selfRef">5.7. </a><a href="#name-cert-not-before-and-cert-no" class="section-name selfRef">Cert-Not-Before and Cert-Not-After HTTP Headers</a>
        </h3>
<p id="section-5.7-1">The "Message Headers" registry has been updated with the following additional values:<a href="#section-5.7-1" class="pilcrow">¶</a></p>
<table class="center" id="table-7">
          <caption><a href="#table-7" class="selfRef">Table 7</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Header Field Name</th>
              <th class="text-left" rowspan="1" colspan="1">Protocol</th>
              <th class="text-left" rowspan="1" colspan="1">Status</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">Cert-Not-Before</td>
              <td class="text-left" rowspan="1" colspan="1">http</td>
              <td class="text-left" rowspan="1" colspan="1">standard</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739, <a href="#fetching-certificates" class="xref">Section 3.3</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">Cert-Not-After</td>
              <td class="text-left" rowspan="1" colspan="1">http</td>
              <td class="text-left" rowspan="1" colspan="1">standard</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8739, <a href="#fetching-certificates" class="xref">Section 3.3</a>
</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
</section>
</div>
<div id="security-considerations">
<section id="section-6">
      <h2 id="name-security-considerations">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<div id="no-revocation">
<section id="section-6.1">
        <h3 id="name-no-revocation">
<a href="#section-6.1" class="section-number selfRef">6.1. </a><a href="#name-no-revocation" class="section-name selfRef">No Revocation</a>
        </h3>
<p id="section-6.1-1">STAR certificates eliminate an important security feature of PKI,
        which is the ability to revoke certificates.  Revocation allows the
        administrator to limit the damage done by a rogue node or an adversary
        who has control of the private key.  With STAR certificates,
        expiration replaces revocation so there is potential for lack of
        timeliness in the revocation taking effect.  To that end, see also the
        discussion on clock skew in <a href="#operational-cons-clocks" class="xref">Section 4.1</a>.<a href="#section-6.1-1" class="pilcrow">¶</a></p>
<p id="section-6.1-2">It should be noted that revocation also has timeliness issues
        because both Certificate Revocation Lists (CRLs) and OCSP responses
        have nextUpdate fields that tell relying parties (RPs) how long they
        should trust this revocation data.  These fields are typically set to
        hours, days, or even weeks in the future.  Any revocation that happens
        before the time in nextUpdate goes unnoticed by the RP.<a href="#section-6.1-2" class="pilcrow">¶</a></p>
<p id="section-6.1-3">One situation where the lack of explicit revocation could create a
        security risk to the IdO is when the Order is created with a
        start-date of some appreciable amount of time in the future.  Recall
        that when authorizations have been fulfilled, the Order moves to the
        "valid" state and the star-certificate endpoint is populated with the
        first cert (<a href="#fig-order-state-transitions-ext" class="xref">Figure 4</a>).  So, if an attacker manages to get hold of the
        private key as well as the first (post-dated) certificate, there is
        a time window in the future when they will be able to successfully
        impersonate the IdO.  Note that cancellation is pointless in this
        case.  In order to mitigate the described threat, it is
        <span class="bcp14">RECOMMENDED</span> that IdO place their Orders at a time that
        is close to the Order's start-date.<a href="#section-6.1-3" class="pilcrow">¶</a></p>
<p id="section-6.1-4">More discussion of the security of STAR certificates is available in
<span>[<a href="#TOPALOVIC" class="xref">TOPALOVIC</a>]</span>.<a href="#section-6.1-4" class="pilcrow">¶</a></p>
</section>
</div>
<div id="denial-of-service-considerations">
<section id="section-6.2">
        <h3 id="name-denial-of-service-considera">
<a href="#section-6.2" class="section-number selfRef">6.2. </a><a href="#name-denial-of-service-considera" class="section-name selfRef">Denial-of-Service Considerations</a>
        </h3>
<p id="section-6.2-1">STAR adds a new attack vector that increases the threat of
        denial-of-service attacks, caused by the change to the CA's
        behavior. Each STAR request amplifies the resource demands upon the
        CA, where one Order produces not one but potentially dozens or
        hundreds of certificates, depending on the auto-renewal "lifetime"
        parameter. An attacker can use this property to aggressively reduce
        the auto-renewal "lifetime" (e.g., 1 second) jointly with other ACME
        attack vectors identified in <span><a href="https://www.rfc-editor.org/rfc/rfc8555#section-10" class="relref">Section 10</a> of [<a href="#RFC8555" class="xref">RFC8555</a>]</span>. Other collateral impact is related to the
        certificate endpoint resource where the client can retrieve the
        certificates periodically. If this resource is external to the CA
        (e.g., a hosted web server), the previous attack will be reflected to
        that resource.<a href="#section-6.2-1" class="pilcrow">¶</a></p>
<p id="section-6.2-2">Mitigation recommendations from ACME still apply, but some of them
        need to be adjusted. For example, applying rate limiting to the
        initial request, due to the nature of the auto-renewal behavior,
        cannot solve the above problem. The CA server needs complementary
        mitigation, and specifically, it <span class="bcp14">SHOULD</span> enforce a
        minimum value on auto-renewal "lifetime". Alternatively, the CA can
        set a rate limit for internal certificate generation processes. Note
        that this limit has to take account of already scheduled renewal
        issuances as well as new incoming requests.<a href="#section-6.2-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="privacy-considerations">
<section id="section-6.3">
        <h3 id="name-privacy-considerations">
<a href="#section-6.3" class="section-number selfRef">6.3. </a><a href="#name-privacy-considerations" class="section-name selfRef">Privacy Considerations</a>
        </h3>
<p id="section-6.3-1">In order to avoid correlation of certificates by account, if
        unauthenticated GET is negotiated (<a href="#certificate-get-nego" class="xref">Section 3.4</a>), the recommendation in <span><a href="https://www.rfc-editor.org/rfc/rfc8555#section-10.5" class="relref">Section 10.5</a> of [<a href="#RFC8555" class="xref">RFC8555</a>]</span> regarding the choice of URL
        structure applies, i.e., servers <span class="bcp14">SHOULD</span> choose URLs of
        certificate resources in a non-guessable way, for example, using
        capability URLs <span>[<a href="#W3C.CAPABILITY-URLS" class="xref">W3C.CAPABILITY-URLS</a>]</span>.<a href="#section-6.3-1" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<section id="section-7">
      <h2 id="name-references">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-7.1">
        <h3 id="name-normative-references">
<a href="#section-7.1" class="section-number selfRef">7.1. </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">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>
<dt id="RFC3339">[RFC3339]</dt>
<dd>
<span class="refAuthor">Klyne, G.</span><span class="refAuthor"> and C. Newman</span>, <span class="refTitle">"Date and Time on the Internet: Timestamps"</span>, <span class="seriesInfo">RFC 3339</span>, <span class="seriesInfo">DOI 10.17487/RFC3339</span>, <time datetime="2002-07">July 2002</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3339">https://www.rfc-editor.org/info/rfc3339</a>&gt;</span>. </dd>
<dt id="RFC7231">[RFC7231]</dt>
<dd>
<span class="refAuthor">Fielding, R., Ed.</span><span class="refAuthor"> and J. Reschke, Ed.</span>, <span class="refTitle">"Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content"</span>, <span class="seriesInfo">RFC 7231</span>, <span class="seriesInfo">DOI 10.17487/RFC7231</span>, <time datetime="2014-06">June 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7231">https://www.rfc-editor.org/info/rfc7231</a>&gt;</span>. </dd>
<dt id="RFC7234">[RFC7234]</dt>
<dd>
<span class="refAuthor">Fielding, R., Ed.</span><span class="refAuthor">, Nottingham, M., Ed.</span><span class="refAuthor">, and J. Reschke, Ed.</span>, <span class="refTitle">"Hypertext Transfer Protocol (HTTP/1.1): Caching"</span>, <span class="seriesInfo">RFC 7234</span>, <span class="seriesInfo">DOI 10.17487/RFC7234</span>, <time datetime="2014-06">June 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7234">https://www.rfc-editor.org/info/rfc7234</a>&gt;</span>. </dd>
<dt id="RFC7807">[RFC7807]</dt>
<dd>
<span class="refAuthor">Nottingham, M.</span><span class="refAuthor"> and E. Wilde</span>, <span class="refTitle">"Problem Details for HTTP APIs"</span>, <span class="seriesInfo">RFC 7807</span>, <span class="seriesInfo">DOI 10.17487/RFC7807</span>, <time datetime="2016-03">March 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7807">https://www.rfc-editor.org/info/rfc7807</a>&gt;</span>. </dd>
<dt id="RFC8126">[RFC8126]</dt>
<dd>
<span class="refAuthor">Cotton, M.</span><span class="refAuthor">, Leiba, B.</span><span class="refAuthor">, and T. Narten</span>, <span class="refTitle">"Guidelines for Writing an IANA Considerations Section in RFCs"</span>, <span class="seriesInfo">BCP 26</span>, <span class="seriesInfo">RFC 8126</span>, <span class="seriesInfo">DOI 10.17487/RFC8126</span>, <time datetime="2017-06">June 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8126">https://www.rfc-editor.org/info/rfc8126</a>&gt;</span>. </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">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>
<dt id="RFC8555">[RFC8555]</dt>
<dd>
<span class="refAuthor">Barnes, R.</span><span class="refAuthor">, Hoffman-Andrews, J.</span><span class="refAuthor">, McCarney, D.</span><span class="refAuthor">, and J. Kasten</span>, <span class="refTitle">"Automatic Certificate Management Environment (ACME)"</span>, <span class="seriesInfo">RFC 8555</span>, <span class="seriesInfo">DOI 10.17487/RFC8555</span>, <time datetime="2019-03">March 2019</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8555">https://www.rfc-editor.org/info/rfc8555</a>&gt;</span>. </dd>
</dl>
</section>
<section id="section-7.2">
        <h3 id="name-informative-references">
<a href="#section-7.2" class="section-number selfRef">7.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="ACER">[ACER]</dt>
<dd>
<span class="refAuthor">Acer, M.E.</span><span class="refAuthor">, Stark, E.</span><span class="refAuthor">, Felt, A.P.</span><span class="refAuthor">, Fahl, S.</span><span class="refAuthor">, Bhargava, R.</span><span class="refAuthor">, Dev, B.</span><span class="refAuthor">, Braithwaite, M.</span><span class="refAuthor">, Sleevi, R.</span><span class="refAuthor">, and P. Tabriz</span>, <span class="refTitle">"Where the Wild Warnings Are: Root Causes of Chrome HTTPS Certificate Errors"</span>, <span class="seriesInfo">DOI 10.1145/3133956.3134007</span>, <time datetime="2017-10">October 2017</time>, <span>&lt;<a href="https://acmccs.github.io/papers/p1407-acerA.pdf">https://acmccs.github.io/papers/p1407-acerA.pdf</a>&gt;</span>. </dd>
<dt id="OBRIEN">[OBRIEN]</dt>
<dd>
<span class="refAuthor">O'Brien, D.</span><span class="refAuthor"> and R. Sleevi</span>, <span class="refTitle">"Chromium Certificate Transparency Policy"</span>, <time datetime="2017-04">April 2017</time>, <span>&lt;<a href="https://github.com/chromium/ct-policy">https://github.com/chromium/ct-policy</a>&gt;</span>. </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">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>
<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">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>
<dt id="I-D.nir-saag-star">[SHORT-TERM-CERTS]</dt>
<dd>
<span class="refAuthor">Nir, Y.</span><span class="refAuthor">, Fossati, T.</span><span class="refAuthor">, Sheffer, Y.</span><span class="refAuthor">, and T. Eckert</span>, <span class="refTitle">"Considerations For Using Short Term Certificates"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-nir-saag-star-01</span>, <time datetime="2018-03-05">5 March 2018</time>, <span>&lt;<a href="https://tools.ietf.org/html/draft-nir-saag-star-01">https://tools.ietf.org/html/draft-nir-saag-star-01</a>&gt;</span>. </dd>
<dt id="I-D.ietf-acme-star-delegation">[STAR-DELEGATION]</dt>
<dd>
<span class="refAuthor">Sheffer, Y.</span><span class="refAuthor">, Lopez, D.</span><span class="refAuthor">, Pastor, A.</span><span class="refAuthor">, and T. Fossati</span>, <span class="refTitle">"An ACME Profile for Generating Delegated STAR Certificates"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-ietf-acme-star-delegation-03</span>, <time datetime="2020-03-08">8 March 2020</time>, <span>&lt;<a href="https://tools.ietf.org/html/draft-ietf-acme-star-delegation-03">https://tools.ietf.org/html/draft-ietf-acme-star-delegation-03</a>&gt;</span>. </dd>
<dt id="STARK">[STARK]</dt>
<dd>
<span class="refAuthor">Stark, E.</span><span class="refAuthor">, Huang, L.S.</span><span class="refAuthor">, Israni, D.</span><span class="refAuthor">, Jackson, C.</span><span class="refAuthor">, and D. Boneh</span>, <span class="refTitle">"The case for prefetching and prevalidating TLS server certificates"</span>, <time datetime="2012-02">February 2012</time>, <span>&lt;<a href="https://crypto.stanford.edu/~dabo/pubs/abstracts/ssl-prefetch.html">https://crypto.stanford.edu/~dabo/pubs/abstracts/ssl-prefetch.html</a>&gt;</span>. </dd>
<dt id="TOPALOVIC">[TOPALOVIC]</dt>
<dd>
<span class="refAuthor">Topalovic, E.</span><span class="refAuthor">, Saeta, B.</span><span class="refAuthor">, Huang, L.S.</span><span class="refAuthor">, Jackson, C.</span><span class="refAuthor">, and D. Boneh</span>, <span class="refTitle">"Towards Short-Lived Certificates"</span>, <time datetime="2012">2012</time>, <span>&lt;<a href="https://www.ieee-security.org/TC/W2SP/2012/papers/w2sp12-final9.pdf">https://www.ieee-security.org/TC/W2SP/2012/papers/w2sp12-final9.pdf</a>&gt;</span>. </dd>
<dt id="W3C.CAPABILITY-URLS">[W3C.CAPABILITY-URLS]</dt>
<dd>
<span class="refAuthor">Tennison, J.</span>, <span class="refTitle">"Good Practices for Capability URLs"</span>, <span class="refContent">W3C First Public Working Draft</span>, <span class="refContent">Latest version available at &lt;https://www.w3.org/TR/capability-urls/&gt;
</span>, <time datetime="2014-02">February 2014</time>, <span>&lt;<a href="https://www.w3.org/TR/2014/WD-capability-urls-20140218">https://www.w3.org/TR/2014/WD-capability-urls-20140218</a>&gt;</span>. </dd>
</dl>
</section>
</section>
<div id="acknowledgments">
<section id="section-appendix.a">
      <h2 id="name-acknowledgments">
<a href="#name-acknowledgments" class="section-name selfRef">Acknowledgments</a>
      </h2>
<p id="section-appendix.a-1">This work is partially supported by the European Commission under
      Horizon 2020 grant agreement no. 688421 Measurement and Architecture for
      a Middleboxed Internet (MAMI). This support does not imply
      endorsement.<a href="#section-appendix.a-1" class="pilcrow">¶</a></p>
<p id="section-appendix.a-2">Thanks to <span class="contact-name">Ben Kaduk</span>, <span class="contact-name">Richard       Barnes</span>, <span class="contact-name">Roman Danyliw</span>, <span class="contact-name">Jon       Peterson</span>, <span class="contact-name">Eric Rescorla</span>, <span class="contact-name">Ryan Sleevi</span>, <span class="contact-name">Sean Turner</span>, <span class="contact-name">Alexey Melnikov</span>, <span class="contact-name">Adam Roach</span>, <span class="contact-name">Martin Thomson</span>, and <span class="contact-name">Mehmet Ersue</span> for helpful comments and
      discussions that have shaped this document.<a href="#section-appendix.a-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="authors-addresses">
<section id="section-appendix.b">
      <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">Diego Lopez</span></div>
<div dir="auto" class="left"><span class="org">Telefonica I+D</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:diego.r.lopez@telefonica.com" class="email">diego.r.lopez@telefonica.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Oscar Gonzalez de Dios</span></div>
<div dir="auto" class="left"><span class="org">Telefonica I+D</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:oscar.gonzalezdedios@telefonica.com" class="email">oscar.gonzalezdedios@telefonica.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Antonio Agustin Pastor Perales</span></div>
<div dir="auto" class="left"><span class="org">Telefonica I+D</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:antonio.pastorperales@telefonica.com" class="email">antonio.pastorperales@telefonica.com</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</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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