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Persona Assertion Token

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This is an older version of an Internet-Draft that was ultimately published as RFC 8225.
Authors Chris Wendt , Jon Peterson
Last updated 2016-02-22
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STIR                                                       C. Wendt, Ed.
Internet-Draft                                                   Comcast
Intended status: Standards Track                             J. Peterson
Expires: August 24, 2016                                    Neustar Inc.
                                                       February 21, 2016

                        Persona Assertion Token


   This document defines a token format for verifying with non-
   repudiation the sender of and authorization to send information
   related to the originator of personal communications.  A
   cryptographic signature is defined to protect the integrity of the
   information used to identify the originator of a personal
   communications session toward a terminating entity.  The
   cryptographic signature is defined with the intention that it can
   confidently verify the originating persona even when the signature is
   sent to the terminating party over a potentially unsecure channel.
   The Persona Assertion Token (PASSporT) is particularly useful for
   many personal communications applications over IP networks and other
   multi-hop interconnection scenarios where the originating and
   terminating parties may not have a direct trusted relationship.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 24, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( 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

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Token Overview  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  PASSporT Definition . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  PASSporT Header . . . . . . . . . . . . . . . . . . . . .   4
       3.1.1.  "typ" (Type) Header Parameter . . . . . . . . . . . .   4
       3.1.2.  "alg" (Algorithm) Header Parameter  . . . . . . . . .   4
       3.1.3.  "x5u" (X.509 URL) Header Parameter  . . . . . . . . .   4
     3.2.  PASSporT Token Claim  . . . . . . . . . . . . . . . . . .   5
     3.3.  PASSporT Signature  . . . . . . . . . . . . . . . . . . .   5
   4.  Extending PASSporT  . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  "ppt" (PASSporT) header parameter . . . . . . . . . . . .   6
     4.2.  Extended PASSporT Claims  . . . . . . . . . . . . . . . .   6
     4.3.  Alternate PASSporT Extension  . . . . . . . . . . . . . .   7
     4.4.  Registering PASSporT Extensions . . . . . . . . . . . . .   7
   5.  Deterministic JSON Serialization  . . . . . . . . . . . . . .   7
   6.  Human Readability . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
     7.1.  Avoidance of replay and cut and paste attacks . . . . . .   8
     7.2.  Solution Considerations . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Media Type Registration . . . . . . . . . . . . . . . . .   9
       8.1.1.  Media Type Registry Contents Additions Requested  . .   9
     8.2.  JSON Web Token Claims Registration  . . . . . . . . . . .  10
       8.2.1.  Registry Contents Additions Requested . . . . . . . .  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   In today's IP-enabled telecommunications world, there is a growing
   concern about the ability to trust incoming invitations for
   communications sessions, including video, voice and messaging.  As an
   example, modern telephone networks provide the ability to spoof the
   telephone number for many legitimate purposes including providing
   network features and services on the behalf of a legitimate telephone

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   number.  However, as we have seen, bad actors have taken advantage of
   this ability for illegitimate and fraudulent purposes meant to trick
   telephone users to believe they are someone they are not.  This
   problem can be extended to many emerging forms of personal

   This document defines a common method for creating and validating a
   token that cryptographically verifies an originating identity, or
   more generally a URI or application specific identity string
   representing the originator of personal communications.  Through
   extended profiles other information associated with the originating
   party or the transport of the personal communications can be attached
   to the token.  The primary goal of PASSporT is to provide a common
   framework for signing persona related information in an extensible
   way.  A secondary goal is to provide this functionality independent
   of any specific personal communications signaling call logic, so that
   creation and verification of persona information can be implemented
   in a flexible way and can be used in many personal communications
   applications including end-to-end applications that require different
   signaling protocol interworking.  It is anticipated that signaling
   protocol specific guidance will be provided in other related
   documents and specifications to specify how to use and transport
   PASSporT tokens, however this is intentionally out of scope for this

   Note: As of the authoring of this document,
   [I-D.ietf-stir-rfc4474bis] provides details of how to use PASSporT
   within SIP signaling for the signing and verification of telephone
   numbers and there is a parallel.

2.  Token Overview

   Tokens are a convenient way of encapsulating information with
   associated digital signatures.  They are used in many applications
   that require authentication, authorization, encryption and other use
   cases.  JSON Web Token (JWT) [RFC7519] and JSON Web Signature (JWS)
   [RFC7515] are designed to provide a compact form for many of these
   purposes and define a specific method and syntax for signing a
   specific set of information or "claims" within the token and
   therefore providing an extensible set of claims.  Additionally, JWS
   provides extensible mechanisms for specifying the method and
   cryptographic algorithms used for the associated digital signatures.

3.  PASSporT Definition

   The PASSporT is constructed based on JWT [RFC7519] and JWS [RFC7515]
   specifications.  JWS defines the use of JSON data structures in a
   specified canonical format for signing data corresponding to JOSE

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   header, JWS Payload, and JWS Signature.  JWT defines specific set of
   claims that are represented by specified key value pairs which can be
   extended with custom keys for specific applications.

3.1.  PASSporT Header

   The JWS token header is a JOSE header [RFC7515] that defines the type
   and encryption algorithm used in the token.

   An example of the header for the case of a RSASSA-PKCS1-v1_5 SHA-256
   digital signature would be the following,

               { "typ":"passport",
                 "x5u":"" }

3.1.1.  "typ" (Type) Header Parameter

   JWS defines the "typ" (Type) Header Parameter to declare the media
   type [IANA.MediaTypes] of the JWS.

   This represents that the encoded token is a JWT, and the JWT is a JWS
   using the RSASSA-PKCS1-v1_5 SHA-256 algorithm.

   For PASSporT Token the "typ" header MUST minimally include and begin
   with "passport".

3.1.2.  "alg" (Algorithm) Header Parameter

   For PASSporT, the "alg" should be defined as RS256 as the recommended
   algorithm.  Note that JWA [RFC7518] defines other algorithms that may
   be utilized or updated in the future depending on cryptographic
   strength requirements guided by current security best practice.

3.1.3.  "x5u" (X.509 URL) Header Parameter

   As defined in JWS, the "x5u" header parameter is used to provide a
   URI [RFC3986] referring to the resource for the X.509 public key
   certificate or certificate chain [RFC5280] corresponding to the key
   used to digitally sign the JWS.  Note: The definition of what the URI
   represents in terms of the actor serving the X.509 public key is out
   of scope of this document.  However, generally this would correspond
   to an HTTPS or DNSSEC resource with the guidance that it MUST be a
   TLS protected, per JWS spec.

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3.2.  PASSporT Token Claim

   The token claim should consist of the information which needs to be
   verified at the terminating party.  This claim should correspond to a
   JWT claim and be encoded as defined by the JWS Payload.

   The PASSporT defines the use of a number of standard JWT defined
   headers as well as two new custom headers corresponding to the two
   parties associated with personal communications, the originator and
   terminator.  These headers or key value pairs are detailed below.

   The JSON claim MUST include the following registered JWT defined

   o  "iat" - issued at, time the JWT was issued, used for expiration.
      This is included for securing the token against replay and cut and
      paste attacks, as explained further in the security considerations
      in section 7.

   Verified Token specific claims that MUST be included:

   o  "orig" - the originating identity claimed. (e.g. for SIP, the FROM
      or P-AssertedID [RFC3325] associated e.164 telephone number, TEL
      or SIP URI) This SHOULD be in URI format as defined in [RFC3986]
      if appropriate but could also be an application specific identity

   o  "term" - the terminating identity claimed as the intended
      destination by the originating party. (e.g. for SIP, the TO
      associated e.164 telephone number, TEL or SIP URI) This SHOULD be
      in URI format as defined in [RFC3986] if appropriate but could
      also be an application specific identity string.

   An example claim is as follows,

               { "iat": 1443208345,
                 "term":"" }

3.3.  PASSporT Signature

   The signature of the PASSporT is created as specified by JWS using
   the private key corresponding to the X.509 public key certificate
   referenced by the "x5u" header parameter.

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4.  Extending PASSporT

   PASSporT represents the bare minimum set of claims needed to assert
   the originating identity, however there will certainly be new and
   extended applications and usage of PASSPorT that will need to
   extending claims to represent other information specific to the
   origination identities beyond the identity itself.

   There are two mechanisms defined to extend PASSporT.  The first
   includes an extension of the base passport claims to include
   additional claims.  An alternative method of extending PASSporT is
   for applications of PASSporT unrelated to the base set of claims,
   that will define it's own set of claims.  Both are described below.

4.1.  "ppt" (PASSporT) header parameter

   For extended profiles of PASSporT, a new JWS header parameter "ppt"
   MUST be used with a string that uniquely identifies the profile
   specification that defines any new claims that would extend the base
   set of claims of PASSporT.

   An example header with an extended PASSporT profile of "foo" is as

               { "typ":"passport",
                 "x5u":"" }

4.2.  Extended PASSporT Claims

   Future specifications that define such extensions to the PASSporT
   mechanism MUST explicitly designate what claims they include, the
   order in which they will appear, and any further information
   necessary to implement the extension.  All extensions MUST
   incorporate the baseline JWT elements specified in Section 3; claims
   may only be appended to the claims object specified in there, they
   can never be subtracted re-ordered.  Specifying new claims follows
   the baseline JWT procedures ([RFC7519] Section 10.1).  Note that
   understanding an extension as a verifier is always optional for
   compliance with this specification (though future specifications or
   profiles for deployment environments may make other "ppt" values
   mandatory).  The creator of a PASSporT object cannot assume that
   verifiers will understand any given extension.  Verifiers that do
   support an extension may then trigger appropriate application-level
   behavior in the presence of an extension; authors of extensions
   should provide appropriate extension-specific guidance to application
   developers on this point.

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4.3.  Alternate PASSporT Extension

   Some applications may want to use the mechanism of the PASSporT
   digital signature that is not a superset of the base set of claims of
   the PASSporT token as defined in Section 3.  Rather, a specification
   may use PASSporT with its own defined set of claims.

   In this case, the specification should define its own MIME media type
   [RFC2046] in the "Media Types" registry [IANA.MediaTypes].  It is
   recommended that the MIME subtype start with the string "passport-"
   to signify that it is related to the PASSporT token.  For example,
   for the "foo" application the MIME type/sub-type could be defined as

4.4.  Registering PASSporT Extensions

   In order for interoperability and maintaining uniqueness of the
   extended PASSporT profile header parameter string, there SHOULD be an
   industry registry that tracks the definition of the profile strings.

5.  Deterministic JSON Serialization

   In order to provide a deterministic representation of the PASSporT
   Header and Claims, particularly if PASSporT is used across multiple
   signaling environments, the JSON header object and JSON Claim object
   MUST be computed as follows.

   The JSON object MUST follow the rules for the construction of the
   thumbprint of a JSON Web Key (JWK) as defined in [RFC7638] Section 3.
   Each JSON object MUST contain no whitespace or line breaks before or
   after any syntactic elements and with the required members ordered
   lexicographically by the Unicode [UNICODE] code points of the member

   In addition, the JSON header and claim members MUST follow the
   lexicographical ordering and character and string rules defined in
   [RFC7638] Section 3.3.

6.  Human Readability

   For many applications, JWT [RFC7519] and JWS [RFC7515] can use Base64
   encoding to the Header and Claims sections as specified.  However,
   many personal communications protocols, such as SIP and XMPP, use a
   "human readable" format to allow for ease of use and ease of
   operational debugging and monitoring.  As such, specifications using
   PASSporT may provide guidance on whether Base64 encoding or plain
   text will be used for the construction of the PASSporT Header and
   Claim sections.

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7.  Security Considerations

7.1.  Avoidance of replay and cut and paste attacks

   There are a number of security considerations for use of the token
   for avoidance of replay and cut and paste attacks.  Verified tokens
   must be sent along with other application level protocol information
   (e.g. for SIP an INVITE as defined in [RFC3261]).  There should be a
   link between various information provided in the token and
   information provided by the application level protocol information.

   These would include:

   o  "iat" claim should closely correspond to a date/time the message
      was originated.  It should also be within a relative delta time
      that is reasonable for clock drift and transmission time
      characteristics associated with the application using the verified

   o  "term" claim is included to prevent the ability to use a
      previously originated message to send to another terminating party

7.2.  Solution Considerations

   It should be recognized that the use of this token should not, in
   it's own right, be considered a full solution for absolute non-
   repudiation of the persona being asserted.  This only provides non-
   repudiation of the signer of PASSporT.  If the signer and the persona
   are not one in the same, which can and often can be the case in
   telecommunications networks today, protecting the terminating party
   for being spoofed may take some interpretation or additional
   verification of the link between the PASSporT signature and the
   persona being asserted.

   In addition, the telecommunications systems and specifications that
   use PASSporT should in practice provide mechanisms for:

   o  Managing X.509 certificates and X.509 certificate chains to an
      authorized trust anchor that can be a trusted entity to all
      participants in the telecommunications network

   o  Accounting for entities that may route calls from other peer or
      interconnected telecommunications networks that are not part of
      the "trusted" communications network or may not be following the
      usage of PASSporT or the profile of PASSporT appropriate to that

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   o  Following best practices around management and security of X.509

8.  IANA Considerations

8.1.  Media Type Registration

8.1.1.  Media Type Registry Contents Additions Requested

   This section registers the "application/passport" media type
   [RFC2046] in the "Media Types" registry [IANA.MediaTypes] in the
   manner described in [RFC6838], which can be used to indicate that the
   content is a PASSporT defined JWT and JWS.

   o  Type name: application

   o  Subtype name: passport

   o  Required parameters: n/a

   o  Optional parameters: n/a

   o  Encoding considerations: 8bit; application/passport values are
      encoded as a series of base64url-encoded values (some of which may
      be the empty string), each separated from the next by a single
      period ('.') character.

   o  Security considerations: See the Security Considerations section
      of RFC 7515.

   o  Interoperability considerations: n/a

   o  Published specification: draft-ietf-stir-passport-00

   o  Applications that use this media type: STIR and other applications
      that require identity related assertion

   o  Fragment identifier considerations: n/a

   o  Additional information:

      *  Magic number(s): n/a

      *  File extension(s): n/a

      *  Macintosh file type code(s): n/a

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   o  Person and email address to contact for further information: Chris

   o  Intended usage: COMMON

   o  Restrictions on usage: none

   o  Author: Chris Wendt,

   o  Change Controller: IESG

   o  Provisional registration?  No

8.2.  JSON Web Token Claims Registration

8.2.1.  Registry Contents Additions Requested

   o  Claim Name: "orig"

   o  Claim Description: Originating Identity String

   o  Change Controller: IESG

   o  Specification Document(s): Section 3.2 of draft-ietf-stir-

   o  Claim Name: "term"

   o  Claim Description: Terminating Identity String

   o  Change Controller: IESG

   o  Specification Document(s): Section 3.2 of draft-ietf-stir-

9.  Acknowledgements

   Particular thanks to members of the ATIS and SIP Forum NNI Task Group
   including Jim McEchern, Martin Dolly, Richard Shockey, John Barnhill,
   Christer Holmberg, Victor Pascual Avila, Mary Barnes, and Eric Burger
   for their review, ideas, and contributions.  Also thanks to Henning
   Schulzrinne, Russ Housley, Alan Johnston, and Richard Barnes for
   valuable feedback on the technical and security aspects of the

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10.  References

              Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-07
              (work in progress), February 2016.

              "IANA, "Media Types"", <Media Types>.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,

   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              DOI 10.17487/RFC3325, November 2002,

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <>.

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   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,

   [RFC7638]  Jones, M. and N. Sakimura, "JSON Web Key (JWK)
              Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
              2015, <>.

   [UNICODE]  "The Unicode Consortium, "The Unicode Standard"",

Authors' Addresses

   Chris Wendt (editor)
   One Comcast Center
   Philadelphia, PA  19103


   Jon Peterson
   Neustar Inc.
   1800 Sutter St Suite 570
   Concord, CA  94520


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