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<pre>Internet Engineering Task Force (IETF) C. Wendt
Request for Comments: 8588 Comcast
Category: Standards Track M. Barnes
ISSN: 2070-1721 iconectiv
May 2019
<span class="h1">Personal Assertion Token (PaSSporT) Extension for Signature-based</span>
<span class="h1">Handling of Asserted information using toKENs (SHAKEN)</span>
Abstract
This document extends the Personal Assertion Token (PASSporT), which
is a token object that conveys cryptographically signed information
about the participants involved in communications. The extension is
defined based on the "Signature-based Handling of Asserted
information using toKENs (SHAKEN)" specification by the ATIS/SIP
Forum IP-NNI Task Group. It provides both (1) a specific set of
levels of confidence in the correctness of the originating identity
of a call originated in a SIP-based telephone network as well as (2)
an identifier that allows the Service Provider (SP) to uniquely
identify the origin of the call within its network.
Status of This Memo
This is an Internet Standards Track document.
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 <a href="./rfc7841#section-2">Section 2 of RFC 7841</a>.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
<a href="https://www.rfc-editor.org/info/rfc8588">https://www.rfc-editor.org/info/rfc8588</a>.
<span class="grey">Wendt & Barnes Standards Track [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc8588">RFC 8588</a> SHAKEN May 2019</span>
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
Provisions Relating to IETF Documents
(<a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a>) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include 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.
Table of Contents
<a href="#section-1">1</a>. Introduction . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-2">2</a>. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-3">3</a>. Overview of "shaken" PASSporT Extension . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-4">4</a>. PASSporT "attest" Claim . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-5">5</a>. PASSporT "origid" Claim . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-6">6</a>. Example "shaken" PASSporT . . . . . . . . . . . . . . . . . . <a href="#page-5">5</a>
<a href="#section-7">7</a>. Using "shaken" in SIP . . . . . . . . . . . . . . . . . . . . <a href="#page-5">5</a>
<a href="#section-8">8</a>. Order of Claim Keys . . . . . . . . . . . . . . . . . . . . . <a href="#page-5">5</a>
<a href="#section-9">9</a>. Security Considerations . . . . . . . . . . . . . . . . . . . <a href="#page-6">6</a>
<a href="#section-10">10</a>. Privacy Considerations . . . . . . . . . . . . . . . . . . . <a href="#page-6">6</a>
<a href="#section-11">11</a>. IANA Considerations . . . . . . . . . . . . . . . . . . . . . <a href="#page-7">7</a>
<a href="#section-11.1">11.1</a>. JSON Web Token claims . . . . . . . . . . . . . . . . . <a href="#page-7">7</a>
<a href="#section-11.2">11.2</a>. PASSporT Types . . . . . . . . . . . . . . . . . . . . . <a href="#page-7">7</a>
<a href="#section-12">12</a>. References . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-7">7</a>
<a href="#section-12.1">12.1</a>. Normative References . . . . . . . . . . . . . . . . . . <a href="#page-7">7</a>
<a href="#section-12.2">12.2</a>. Informative References . . . . . . . . . . . . . . . . . <a href="#page-8">8</a>
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
<span class="grey">Wendt & Barnes Standards Track [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc8588">RFC 8588</a> SHAKEN May 2019</span>
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
The Signature-based Handling of Asserted information using toKENs
(SHAKEN) [<a href="#ref-ATIS-1000074">ATIS-1000074</a>] specification defines a framework for using
Secure Telephone Identity Revisited (STIR) protocols including the
Personal Assertion Token (PASSporT) [<a href="./rfc8225" title=""PASSporT: Personal Assertion Token"">RFC8225</a>], SIP Authenticated
Identity Management [<a href="./rfc8224" title=""Authenticated Identity Management in the Session Initiation Protocol (SIP)"">RFC8224</a>], and the STIR certificate framework
[<a href="./rfc8226" title=""Secure Telephone Identity Credentials: Certificates"">RFC8226</a>] for implementing the cryptographic validation of an
authorized originator of telephone calls using SIP. Because the
current telephone network contains traffic originated from both VoIP
and TDM/SS7 (Time Division Multiplexing / Signaling System 7), there
are many scenarios that need to be accounted for where PASSporT
signatures may represent either direct or indirect call origination
scenarios. The SHAKEN [<a href="#ref-ATIS-1000074">ATIS-1000074</a>] specification defines levels of
attestation of the origination of the call as well as an origination
identifier that can help create a unique association between the
origin of a particular call to the point in the VoIP or TDM telephone
network the call came from to identify, for example, either a
customer or class of service that call represents. This document
specifies these values as claims to extend the base set of PASSporT
claims.
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Terminology</span>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
<a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a> [<a href="./rfc2119" title=""Key words for use in RFCs to Indicate Requirement Levels"">RFC2119</a>] [<a href="./rfc8174" title=""Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"">RFC8174</a>] when, and only when, they appear in all
capitals, as shown here.
In addition, the following terms are used in this document:
o Verified association: Typically defined as an authenticated
relationship between a customer and a device that initiated a call
on behalf of that customer, for example, a subscriber account with
a specific SIM card or set of SIP credentials.
o PASSporT: Defined in [<a href="./rfc8225" title=""PASSporT: Personal Assertion Token"">RFC8225</a>] is a JSON Web Token [<a href="./rfc7519" title=""JSON Web Token (JWT)"">RFC7519</a>]
defined specifically for securing the identity of an initiator of
personal communication. This document defines a specific
extension to PASSporT.
<span class="grey">Wendt & Barnes Standards Track [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc8588">RFC 8588</a> SHAKEN May 2019</span>
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. Overview of "shaken" PASSporT Extension</span>
The SHAKEN framework is designed to use PASSporT [<a href="./rfc8225" title=""PASSporT: Personal Assertion Token"">RFC8225</a>] as a
method of asserting the caller's telephone identity. In addition to
the PASSporT base claims, there are two additional claims that have
been defined for the needs of a service provider to signal
information beyond just the telephone identity. First, in order to
help bridge the transition of the state of the current telephone
network (which has calls with no authentication and non-SIP [<a href="./rfc3261" title=""SIP: Session Initiation Protocol"">RFC3261</a>]
signaling not compatible with the use of PASSporT and Secure
Telephone Identity (STI) in general), there is an attestation claim.
This provides three levels of attestation: a full attestation when
the service provider can fully attest to the calling identity, a
partial attestation when the service provider originated a telephone
call but cannot fully attest to the calling identity, and a gateway
attestation, which is the lowest level of attestation and represents
the service provider receiving a call from a telephone gateway that
does not support PASSporT or STI.
The second claim is a unique origination identifier that should be
used by the service provider to identify different sources of
telephone calls to support a traceback mechanism that can be used for
enforcement and identification of a source of illegitimate calls.
The use of the compact form of PASSporT is not specified in this
document and is not specified for use in SHAKEN [<a href="#ref-ATIS-1000074">ATIS-1000074</a>].
The next two sections define these new claims.
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. PASSporT "attest" Claim</span>
This indicator allows for both identifying the service provider that
is vouching for the call as well as clearly indicating what
information the service provider is attesting to. The "attest" claim
can be one of the following three values: 'A', 'B', or 'C'. These
values correspond to 'Full Attestation', 'Partial Attestation', and
'Gateway Attestation', respectively. See [<a href="#ref-ATIS-1000074">ATIS-1000074</a>] for the
definitions of these three levels of attestation.
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. PASSporT "origid" Claim</span>
The purpose of the "origid" claim is described in [<a href="#ref-ATIS-1000074">ATIS-1000074</a>].
The value of "origid" claim is a Universally Unique Identifier (UUID)
as defined in [<a href="./rfc4122" title=""A Universally Unique IDentifier (UUID) URN Namespace"">RFC4122</a>]. Please refer to <a href="#section-10">Section 10</a> for a discussion
of the privacy considerations around the use of this value.
<span class="grey">Wendt & Barnes Standards Track [Page 4]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-5" ></span>
<span class="grey"><a href="./rfc8588">RFC 8588</a> SHAKEN May 2019</span>
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. Example "shaken" PASSporT</span>
Protected Header
{
"alg":"ES256",
"typ":"passport",
"ppt":"shaken",
"x5u":"https://cert.example.org/passport.cer"
}
Payload
{
"attest":"A"
"dest":{"tn":["12155550131"]}
"iat":"1443208345",
"orig":{"tn":"12155550121"},
"origid":"123e4567-e89b-12d3-a456-426655440000"
}
<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. Using "shaken" in SIP</span>
The use of the "shaken" PASSporT type and the "attest" and "origid"
claims for SIP is formally defined in [<a href="#ref-ATIS-1000074">ATIS-1000074</a>] using the SIP
[<a href="./rfc3261" title=""SIP: Session Initiation Protocol"">RFC3261</a>] Identity header field defined in [<a href="./rfc8224" title=""Authenticated Identity Management in the Session Initiation Protocol (SIP)"">RFC8224</a>].
<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. Order of Claim Keys</span>
The order of the claim keys MUST follow the rules of <a href="./rfc8225#section-9">Section 9 of
[RFC8225]</a>; the claim keys MUST appear in lexicographic order.
Therefore, the claim keys discussed in this document appear in the
PASSporT Payload in the following order:
o attest
o dest
o iat
o orig
o origid
<span class="grey">Wendt & Barnes Standards Track [Page 5]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-6" ></span>
<span class="grey"><a href="./rfc8588">RFC 8588</a> SHAKEN May 2019</span>
<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. Security Considerations</span>
This document defines a new PASSporT [<a href="./rfc8225" title=""PASSporT: Personal Assertion Token"">RFC8225</a>] extension. The
considerations related to the security of the PASSporT object itself
are the same as those described in [<a href="./rfc8225" title=""PASSporT: Personal Assertion Token"">RFC8225</a>].
[<a id="ref-RFC8224">RFC8224</a>] defines how to compare the values of the "dest", "orig",
and "iat" claims against fields in a SIP message containing a
PASSporT as part of validating that request. The values of the new
"attest" and "origid" claims added by this extension are not used in
such a validation step. They are not compared to fields in the SIP
message. Instead, they simply carry additional information from the
signer to the consumer of the PASSporT. This new information shares
the same integrity protection and non-repudiation properties as the
base claims in the PASSporT.
<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>. Privacy Considerations</span>
As detailed in <a href="./rfc3261#section-26">Section 26 of [RFC3261]</a>, SIP messages inherently carry
identifying information of the caller and callee. The addition of
STIR cryptographically attests that the signing party vouches for the
information given about the callee, as is discussed in the Privacy
Considerations of [<a href="./rfc8224" title=""Authenticated Identity Management in the Session Initiation Protocol (SIP)"">RFC8224</a>].
SHAKEN [<a href="#ref-ATIS-1000074">ATIS-1000074</a>] furthermore adds an "origid" value to the STIR
PASSporT, which is an opaque unique identifier representing an
element on the path of a given SIP request. This identifier is
generated by an originating telephone service provider to identify
where within their network (e.g. a gateway or particular service
element) a call was initiated; "origid" can facilitate forensic
analysis of call origins when identifying and stopping bad actors
trying to spoof identities or make fraudulent calls.
The opacity of the "origid" claim value is intended to minimize
exposure of information about the origination of calls labeled with
an "origid" value. It is therefore RECOMMENDED that implementations
generate a unique "origid" value per call in such a way that only the
generator of the "origid" can determine when two "origid" values
represent the same or different elements. If deployed systems
instead use a common or related "origid" for service elements in
their network, the potential for discovering patterns through
correlation of those calls exists. This could allow a recipient of
calls to, for instance, learn that a set of callers are using a
particular service or coming through a common gateway. It is
expected that SHAKEN PASSporTs are shared only within an [<a href="./rfc3324" title=""Short Term Requirements for Network Asserted Identity"">RFC3324</a>]
trust domain and will be stripped before calls exit that trust
domain, but this information still could be used by analytics on
<span class="grey">Wendt & Barnes Standards Track [Page 6]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-7" ></span>
<span class="grey"><a href="./rfc8588">RFC 8588</a> SHAKEN May 2019</span>
intermediary and terminating systems to reveal information that could
include geographic location and even device-level information,
depending on how the "origid" is generated.
<span class="h2"><a class="selflink" id="section-11" href="#section-11">11</a>. IANA Considerations</span>
<span class="h3"><a class="selflink" id="section-11.1" href="#section-11.1">11.1</a>. JSON Web Token claims</span>
IANA has added two new claims to the "JSON Web Token Claims" registry
as defined in [<a href="./rfc7519" title=""JSON Web Token (JWT)"">RFC7519</a>].
Claim Name: attest
Claim Description: Attestation level as defined in SHAKEN framework
Change Controller: IESG
Specification Document(s): <a href="./rfc8588">RFC 8588</a>
Claim Name: origid
Claim Description: Originating Identifier as defined in SHAKEN
framework
Change Controller: IESG
Specification Document(s): <a href="./rfc8588">RFC 8588</a>
<span class="h3"><a class="selflink" id="section-11.2" href="#section-11.2">11.2</a>. PASSporT Types</span>
IANA has added a new entry in the "Personal Assertion Token
(PASSporT) Extensions" registry for the type "shaken", which is
specified in this document.
<span class="h2"><a class="selflink" id="section-12" href="#section-12">12</a>. References</span>
<span class="h3"><a class="selflink" id="section-12.1" href="#section-12.1">12.1</a>. Normative References</span>
[<a id="ref-ATIS-1000074">ATIS-1000074</a>]
ATIS/SIP Forum IP-NNI Task Group, "Signature-based
Handling of Asserted information using toKENs (SHAKEN)",
January 2017, <<a href="https://access.atis.org/apps/group_public/download.php/32237/ATIS-1000074.pdf">https://access.atis.org/apps/group_public/</a>
<a href="https://access.atis.org/apps/group_public/download.php/32237/ATIS-1000074.pdf">download.php/32237/ATIS-1000074.pdf</a>>.
[<a id="ref-RFC2119">RFC2119</a>] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>,
DOI 10.17487/RFC2119, March 1997,
<<a href="https://www.rfc-editor.org/info/rfc2119">https://www.rfc-editor.org/info/rfc2119</a>>.
[<a id="ref-RFC4122">RFC4122</a>] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", <a href="./rfc4122">RFC 4122</a>,
DOI 10.17487/RFC4122, July 2005,
<<a href="https://www.rfc-editor.org/info/rfc4122">https://www.rfc-editor.org/info/rfc4122</a>>.
<span class="grey">Wendt & Barnes Standards Track [Page 7]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-8" ></span>
<span class="grey"><a href="./rfc8588">RFC 8588</a> SHAKEN May 2019</span>
[<a id="ref-RFC7519">RFC7519</a>] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", <a href="./rfc7519">RFC 7519</a>, DOI 10.17487/RFC7519, May 2015,
<<a href="https://www.rfc-editor.org/info/rfc7519">https://www.rfc-editor.org/info/rfc7519</a>>.
[<a id="ref-RFC8174">RFC8174</a>] Leiba, B., "Ambiguity of Uppercase vs Lowercase in <a href="./rfc2119">RFC</a>
<a href="./rfc2119">2119</a> Key Words", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc8174">RFC 8174</a>, DOI 10.17487/RFC8174,
May 2017, <<a href="https://www.rfc-editor.org/info/rfc8174">https://www.rfc-editor.org/info/rfc8174</a>>.
[<a id="ref-RFC8224">RFC8224</a>] Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
"Authenticated Identity Management in the Session
Initiation Protocol (SIP)", <a href="./rfc8224">RFC 8224</a>,
DOI 10.17487/RFC8224, February 2018,
<<a href="https://www.rfc-editor.org/info/rfc8224">https://www.rfc-editor.org/info/rfc8224</a>>.
[<a id="ref-RFC8225">RFC8225</a>] Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
Token", <a href="./rfc8225">RFC 8225</a>, DOI 10.17487/RFC8225, February 2018,
<<a href="https://www.rfc-editor.org/info/rfc8225">https://www.rfc-editor.org/info/rfc8225</a>>.
[<a id="ref-RFC8226">RFC8226</a>] Peterson, J. and S. Turner, "Secure Telephone Identity
Credentials: Certificates", <a href="./rfc8226">RFC 8226</a>,
DOI 10.17487/RFC8226, February 2018,
<<a href="https://www.rfc-editor.org/info/rfc8226">https://www.rfc-editor.org/info/rfc8226</a>>.
<span class="h3"><a class="selflink" id="section-12.2" href="#section-12.2">12.2</a>. Informative References</span>
[<a id="ref-RFC3261">RFC3261</a>] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", <a href="./rfc3261">RFC 3261</a>,
DOI 10.17487/RFC3261, June 2002,
<<a href="https://www.rfc-editor.org/info/rfc3261">https://www.rfc-editor.org/info/rfc3261</a>>.
[<a id="ref-RFC3324">RFC3324</a>] Watson, M., "Short Term Requirements for Network Asserted
Identity", <a href="./rfc3324">RFC 3324</a>, DOI 10.17487/RFC3324, November 2002,
<<a href="https://www.rfc-editor.org/info/rfc3324">https://www.rfc-editor.org/info/rfc3324</a>>.
<span class="grey">Wendt & Barnes Standards Track [Page 8]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-9" ></span>
<span class="grey"><a href="./rfc8588">RFC 8588</a> SHAKEN May 2019</span>
Acknowledgements
The authors would like to thank those that helped review and
contribute to this document including specific contributions from Jon
Peterson, Russ Housley, Robert Sparks, and Andrew Jurczak. The
authors would like to acknowledge the work of the ATIS/SIP Forum
IP-NNI Task Force to develop the concepts behind this document.
Authors' Addresses
Chris Wendt
Comcast
One Comcast Center
Philadelphia, PA 19103
United States of America
Email: chris-ietf@chriswendt.net
Mary Barnes
iconectiv
Email: mary.ietf.barnes@gmail.com
Wendt & Barnes Standards Track [Page 9]
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