Persona Assertion Token
draft-ietf-stir-passport-07

STIR                                                            C. Wendt
Internet-Draft                                                   Comcast
Intended status: Standards Track                             J. Peterson
Expires: March 13, 2017                                     Neustar Inc.
                                                       September 9, 2016

                        Persona Assertion Token
                      draft-ietf-stir-passport-07

Abstract

   This document defines a canonical string object or 'token' including
   a digital signature for verifying the author of the token, their
   authority to author the token and the information asserted in the
   token, minimally, the originating identity or 'persona' corresponding
   specifically to the originator of 'personal communications', or
   signalled communications between a set of parties with identities.
   The PASSporT token is cryptographically signed to protect the
   integrity of the identify the originator of a personal communications
   session (e.g. the telephone number or URI) and verify the assertion
   of the identity information at the destination.  The cryptographic
   signature is defined with the intention that it can confidently
   verify the originating persona even when the signature is sent to the
   destination party over an insecure channel.  PASSporT is particularly
   useful for many personal communications applications over IP networks
   and other multi-hop interconnection scenarios where the originating
   and destination 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
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   This Internet-Draft will expire on March 13, 2017.

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Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  PASSporT Token Overview . . . . . . . . . . . . . . . . . . .   4
   3.  PASSporT Header . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  "typ" (Type) Header Parameter . . . . . . . . . . . . . .   4
     3.2.  "alg" (Algorithm) Header Parameter  . . . . . . . . . . .   4
     3.3.  "x5u" (X.509 URL) Header Parameter  . . . . . . . . . . .   5
     3.4.  Example PASSporT header . . . . . . . . . . . . . . . . .   5
   4.  PASSporT Payload  . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  JWT defined claims  . . . . . . . . . . . . . . . . . . .   5
       4.1.1.  "iat" - Issued At claim . . . . . . . . . . . . . . .   6
     4.2.  PASSporT specific claims  . . . . . . . . . . . . . . . .   6
       4.2.1.  Originating and Destination Identity Claims . . . . .   6
         4.2.1.1.  "tn" - Telephone Number identity  . . . . . . . .   7
         4.2.1.2.  "uri" - URI identity  . . . . . . . . . . . . . .   7
         4.2.1.3.  Future identity forms . . . . . . . . . . . . . .   7
         4.2.1.4.  Examples  . . . . . . . . . . . . . . . . . . . .   7
       4.2.2.  "mky" - Media Key claim . . . . . . . . . . . . . . .   8
   5.  PASSporT Signature  . . . . . . . . . . . . . . . . . . . . .   9
   6.  Extending PASSporT  . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  "ppt" (PASSporT) header parameter . . . . . . . . . . . .  10
     6.2.  Extended PASSporT Claims  . . . . . . . . . . . . . . . .  10
   7.  Deterministic JSON Serialization  . . . . . . . . . . . . . .  11
     7.1.  Example PASSport deterministic JSON form  . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
     8.1.  Avoidance of replay and cut and paste attacks . . . . . .  12
     8.2.  Solution Considerations . . . . . . . . . . . . . . . . .  13
     8.3.  Privacy Considerations  . . . . . . . . . . . . . . . . .  13
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Media Type Registration . . . . . . . . . . . . . . . . .  13
       9.1.1.  Media Type Registry Contents Additions Requested  . .  13
     9.2.  JSON Web Token Claims Registration  . . . . . . . . . . .  15

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       9.2.1.  Registry Contents Additions Requested . . . . . . . .  15
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     11.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Appendix A.  Example PASSporT JWS Serialization and Signature . .  17
     A.1.  X.509 Private Key Certificate for Example . . . . . . . .  19
     A.2.  X.509 Public Key Certificate for Example  . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

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.
   [RFC7340] As an example, modern telephone networks provide the
   ability to spoof the calling party telephone number for many
   legitimate purposes including providing network features and services
   on the behalf of a legitimate telephone 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 communications.

   This document defines a method for creating and validating a token
   that cryptographically verifies an originating identity, or more
   generally a URI or telephone number representing the originator of
   personal communications.  Through extensions defined in this
   document, in Section 5.2, other information relevant to the personal
   communications can also be added to the token.  The goal of PASSporT
   is to provide a common framework for signing originating identity
   related information in an extensible way.  Additionally, this
   functionality is independent of any specific personal communications
   signaling call logic, so that the assertion of originating identity
   related information can be implemented in a flexible way and can be
   used in applications including end-to-end applications that require
   different signaling protocols or gateways between different
   communications systems.  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 document.

   [I-D.ietf-stir-rfc4474bis] provides details of the use of PASSporT
   within the SIP [RFC3261] signaling protocol for the signing and
   verification of telephone numbers.

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2.  PASSporT Token Overview

   JSON Web Token (JWT) [RFC7519] and JSON Web Signature (JWS) [RFC7515]
   and related specifications define a standard token format that can be
   used as a way of encapsulating claimed or asserted information with
   an associated digital signature using X.509 based certificates.  JWT
   provides a set of claims in JSON format that can conveniently
   accommodate asserted originating identity information and is easily
   extensible for extension mechanisms defined below.  Additionally, JWS
   provides a path for updating methods and cryptographic algorithms
   used for the associated digital signatures.

   JWS defines the use of JSON data structures in a specified canonical
   format for signing data corresponding to JOSE header, JWS Payload,
   and JWS Signature.  JWT defines a set of claims that are represented
   by specified key value pairs which can be extended with custom keys
   for specific applications.  The next sections define the header and
   claims that MUST be minimally used with JWT and JWS for PASSporT.

3.  PASSporT Header

   The JWS token header is a JOSE header [RFC7515] Section 4, that
   defines the type and encryption algorithm used in the token.

   PASSporT header should include, at a minimum, the following header
   parameters defined the the next three subsections.

3.1.  "typ" (Type) Header Parameter

   The "typ" (Type) Header Parameter is defined in JWS Section 4.1.9. to
   declare the media type of the complete JWS.

   For PASSporT Token the "typ" header MUST be the string "passport".
   This represents that the encoded token is a JWT of type passport.

3.2.  "alg" (Algorithm) Header Parameter

   The "alg" (Algorithm) Header Parameter is defined in JWS
   Section 4.1.1.  This definition includes the ability to specify the
   use of a cryptographic algorithm for the signature part of the JWS.
   It also refers to a list of defined "alg" values as part of a
   registry established by JSON Web Algorithms (JWA) [RFC7518] and
   defined in Section 3.1.

   For the creation and verification of PASSporT tokens and their
   digital signatures ES256 MUST be implemented as defined in JWA
   Section 3.4

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   Note that JWA defines other algorithms that may be utilized or
   updated in the future depending on cryptographic strength
   requirements guided by current security best practice.

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

   As defined in JWS Section 4.1.5., the "x5u" header parameter defines
   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.  Generally, as defined in JWS section
   4.1.5, this would correspond to an HTTPS or DNSSEC resource using
   integrity protection.

3.4.  Example PASSporT header

   An example of the header, would be the following, including the
   specified passport type, ES256 algorithm, and a URI referencing the
   network location of the certificate needed to validate the PASSporT
   signature.

       {
           "typ":"passport",
           "alg":"ES256",
           "x5u":"https://cert.example.org/passport.cer"
       }

4.  PASSporT Payload

   The token claims consist of the information which needs to be
   verified at the destination party.  These claims follow the
   definition of a JWT claim [RFC7519] Section 4 and be encoded as
   defined by the JWS Payload [RFC7515] Section 3.

   PASSporT defines the use of a standard JWT defined claim as well as
   custom claims corresponding to the two parties associated with
   personal communications, the originator and destination as detailed
   below.

   Any claim key values outside the US-ASCII range should be encoded
   using percent encoding as described in section 2.1 of [RFC3986], case
   normalized as described in 6.2.2.1 of [RFC3986].

4.1.  JWT defined claims

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4.1.1.  "iat" - Issued At claim

   The JSON claim MUST include the "iat" [RFC7519] Section 4.1.6 defined
   claim Issued At.  As defined this should be set to the date and time
   of the origination of the personal communications.  The time value
   should be of the format defined in [RFC7519] Section 2 NumericDate.
   This is included for securing the token against replay and cut and
   paste attacks, as explained further in the security considerations in
   section 6.

4.2.  PASSporT specific claims

4.2.1.  Originating and Destination Identity Claims

   PASSporT defines claims that convey the identity of the origination
   and destination of personal communications.  Origination in the
   context of PASSporT and for a given application's use of PASSporT is
   the point in the network that has the authority to assert the callers
   identity.  This authority is represented in PASSporT by the
   certificate holder and is signed at the applications choice of
   authoritative point(s) in the network, for example, at a device that
   has authenticated with a user, or at a network entity with an
   authenticated trust relationship with that device and its user.
   Destination represents the intended destination of the personal
   communications, i.e. the identity(s) being called by the caller, The
   destination point(s) determined by the application must have the
   capability to verify the PASSporT token and the digital signature.
   The PASSporT associated certificate is used to validate the authority
   of the originating signer, generally via a certificate chain to the
   trust anchor for that application.

   The origination and destination identities are represented by two
   claims that are required for PASSporT, the "orig" and "dest" claims.
   Both "orig" and "dest" MUST have claims where the key represents an
   identity type and the value is the identity string, both defined in
   subsequent subsections.  Currently, these identities can be
   represented as either telephone numbers or Uniform Resource
   Indicators (URIs).

   The "orig" JSON object MUST only have one key value pair representing
   the asserted identity of any type (currently either "tn" or "uri") of
   the originator of the personal communications signaling.

   The "dest" JSON object MUST have at least have one key value pair,
   but could have multiple identity types (i.e. "tn" and/or "uri") but
   only one of each.  If both "tn" and "uri" are included, the JSON
   object should list the "tn" array first and the "uri" array second.
   Within the "tn" and "uri" arrays, the identity strings should be put

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   in lexicographical order including the scheme-specific portion of the
   URI characters.  Additionally, in the case of "dest" only, the
   identity type key value MUST be an array signaled by standard JSON
   brackets, even when there is a single identity value in the identity
   type key value.

4.2.1.1.  "tn" - Telephone Number identity

   If the originating or destination identity is a telephone number, the
   key representing the identity MUST be "tn".

   Telephone Number strings for "tn" MUST be canonicalized according to
   the procedures specified in [I-D.ietf-stir-rfc4474bis] Section 8.3.

4.2.1.2.  "uri" - URI identity

   If any of the originating or destination identities is of the form
   URI, as defined in [RFC3986], the key representing the identity MUST
   be "uri" URI form of the identity.

4.2.1.3.  Future identity forms

   We recognize that in the future there may be other standard
   mechanisms for representing identities.  The "orig" and "dest" claims
   currently support "tn" and "uri" but could be extended in the future
   to allow for other identity types with new IANA registered unique
   types to represent these forms.

4.2.1.4.  Examples

   Single Originator, with telephone number identity +12155551212, to
   Single Destination, with URI identity 'sip:alice@example.com',
   example:

       {
           "dest":{"uri":["sip:alice@example.com"]},
           "iat":"1443208345",
           "orig":{"tn":"12155551212"}
       }

   Single Originator, with telephone number identity +12155551212, to
   Multiple Destination Identities, with telephone number identity
   +12125551212 and two URI identities, sip:alice@example.com and
   sip:bob@example.com, example:

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       {
           "dest":{
                   "tn":["12125551212"],
                   "uri":["sip:alice@example.com",
                       "sip:bob@example.net"]
           },
           "iat":"1443208345",
           "orig":{"tn":"12155551212"}
       }

4.2.2.  "mky" - Media Key claim

   Some protocols that use PASSporT may also want to protect media
   security keys delivered within their signaling in order to bind those
   keys to the identities established in the signaling layers.  The
   "mky" is an optional PASSporT claim defining the assertion of media
   key fingerprints carried in SDP [RFC4566] via the "a=fingerprint"
   attribute [RFC4572] Section 5.  This claim can support either a
   single or multiple fingerprints appearing in a single SDP body
   corresponding to one or more media streams offered.

   The "mky" claim MUST be formated in a JSON form including the "alg"
   and "dig" keys with the corresponding algorithm and hexadecimal
   values.  If there are more that one fingerprint values associated
   with different media streams in SDP, the fingerprint values MUST be
   constructed as a JSON array denoted by bracket characters.

   For the "dig" key value, the hash value MUST be the hexadecimal value
   without any colons.  The "mky" array MUST order the JSON objects
   containing both "alg" and "dig" key values in lexicographic order of
   the "alg" string first followed by the corresponding lexicographic
   order of the "dig" string values.  Within each of those objects the
   JSON keys MUST have "alg" first and "dig" second.

   An example claim with "mky" claim is as follows:

   For an SDP offer that includes the following fingerprint values,

       a=fingerprint:sha-256 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:
       5D:49:6B:19:E5:7C:AB:3E:4B:65:2E:7D:46:3F:54:42:CD:54:F1
       a=fingerprint:sha-256 02:1A:CC:54:27:AB:EB:9C:53:3F:3E:4B:65:
       2E:7D:46:3F:54:42:CD:54:F1:7A:03:A2:7D:F9:B0:7F:46:19:B2

   the PASSporT Payload object would be:

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       {
           "dest":{"uri":["sip:alice@example.com"]},
           "iat":"1443208345",
           "mky":[
           {
              "alg":"sha-256",
              "dig":"021ACC5427ABEB9C533F3E4B652E7D463F5442CD54
               F17A03A27DF9B07F4619B2"
           },
           {
              "alg":"sha-256",
              "dig":"4AADB9B13F82183B540212DF3E5D496B19E57C
               AB3E4B652E7D463F5442CD54F1"
           }
           ],
           "orig":{"tn":"12155551212"}
       }

5.  PASSporT Signature

   The signature of the PASSporT is created as specified by JWS
   [RFC7515] Section 5.1 Steps 1 through 6.  PASSporT MUST use the JWS
   Protected Header.  For the JWS Payload and the JWS Protected Header,
   the lexicographic ordering and white space rules described above, and
   JSON serialization rules in Section 6 of this document MUST be
   followed.

   Appendix A of this document has a detailed example of how to follow
   the steps to create the JWS Signature.

   JWS [RFC7515] Section 5.1 Step 7 JWS JSON serialization is not
   supported for PASSporT.

   JWS [RFC7515] Section 5.1 Step 8 describes the method to create the
   final JWS Compact Serialization form of the PASSporT Token.

6.  Extending PASSporT

   PASSporT includes the bare minimum set of claims needed to securely
   assert the originating identity and support the secure properties
   discussed in various parts of this document.  JWT supports a straight
   forward way to add additional claims by simply adding new claim key
   pairs.  PASSporT can be extended beyond the defined base set of
   claims to represent other information requiring assertion or
   validation beyond the originating identity itself as needed.

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6.1.  "ppt" (PASSporT) header parameter

   For extension of the base set of claims defined in this document, a
   new JWS header parameter "ppt" MUST be used with a unique string.
   Any PASSporT extension should be defined in a specification
   describing the PASSporT extension and the string used in the "ppt"
   header string that defines any new claims that would extend the base
   set of claims of PASSporT.

   An example header with a PASSporT extension type of "foo" is as
   follows:

       {
           "alg":"ES256",
           "ppt":"foo",
           "typ":"passport",
           "x5u":"https://tel.example.org/passport.cer"
       }

6.2.  Extended PASSporT Claims

   Specifications that define extensions to the PASSporT mechanism MUST
   explicitly specify what claims they include beyond the base set of
   claims from this document, the order in which they will appear, and
   any further information necessary to implement the extension.  All
   extensions MUST include the baseline JWT elements specified in
   Section 3; claims may only be appended to the claims object
   specified; they can never be removed or re-ordered.  Specifying new
   claims follows the baseline JWT procedures ([RFC7519] Section 10.1).
   Understanding an extension or new claims defined by the extension on
   the destination verification of the PASSporT token is optional.  The
   creator of a PASSporT object cannot assume that destination systems
   will understand any given extension.  Verification of PASSporT tokens
   by destination systems 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.

   An example set of extended claims, extending the first example in
   Section 4.1.2.4. using "bar" as the newly defined claim would be as
   follows:

       {
           "bar":"beyond all recognition"
           "dest":{"uri":["sip:alice@example.com"]},
           "iat":"1443208345",
           "orig":{"tn":"12155551212"}
       }

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7.  Deterministic JSON Serialization

   JSON, as a canonical format, can include spaces, line breaks and key
   value pairs can occur in any order and therefore makes it, from a
   string format, non-deterministic.  In order to make the digital
   signature verification work deterministically, the JSON
   representation of the PASSporT Header and Claims, particularly if
   PASSporT is used across multiple signaling environments, specifically
   the JWS Protected Header object and JWS Payload 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
   Step 1 only.  Step 2 MUST NOT be performed; as noted in JWK this is
   still a legal JWK object.

   The PASSporT header and claim direct members MUST follow the
   lexicographical ordering rules.  Any top level JSON members that
   contain JSON objects or arrays, such as "dest" or "mky" MUST follow
   their own lexicographical ordering and whitespace and line break
   rules for the sub-elements.  This includes any header or claims
   defined in future specifications using PASSporT.

7.1.  Example PASSport deterministic JSON form

   This section demonstrate the deterministic JSON serialization for the
   example PASSporT Payload shown in Section 4.2.2.

   The initial JSON object is shown here:

       {
           "dest":{"uri":["sip:alice@example.com"]},
           "orig":{"tn":"12155551212"}
           "iat":"1443208345",
           "mky":[
           {
              "alg":"sha-256",
              "dig":"021ACC5427ABEB9C533F3E4B652E7D463F5442CD54
                  F17A03A27DF9B07F4619B2"
           },
           {
              "alg":"sha-256",
              "dig":"4AADB9B13F82183B540212DF3E5D496B19E57C
                  AB3E4B652E7D463F5442CD54F1"
           }
         ],
       }

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   The parent members of the JSON object are as follows:

   o  "dest"

   o  "orig"

   o  "iat"

   o  "mky"

   Their lexicographic order is:

   o  "dest"

   o  "iat"

   o  "mky"

   o  "orig"

   The final constructed deterministic JSON serialization
   representation, with whitespace and line breaks removed, (with line
   breaks used for display purposes only) is:

     {"dest":{"uri":["sip:alice@example.com"],"iat":1443208345,"mky":
       [{"alg":"sha-256","dig":"021ACC5427ABEB9C533F3E4B652E7D463F5442
       CD54F17A03A27DF9B07F4619B2"},{"alg":"sha-256","dig":"4AADB9B13F
       82183B540212DF3E5D496B19E57CAB3E4B652E7D463F5442CD54F1"}],
       "orig":{"tn":"12155551212"}}

8.  Security Considerations

8.1.  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.  PASSporT tokens
   should be sent with other application level protocol information
   (e.g. for SIP an INVITE as defined in [RFC3261]).  In order to make
   the token signature unique to a specific origination of personal
   communications there should be a link between various information
   provided in the token and information provided by the application
   level protocol information.  This uniqueness specified using the
   following two claims:

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

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      Therefore, validation of the token should consider date and time
      correlation, which could be influenced by signaling protocol
      specific use and network time differences.

   o  'dest' claim is included to prevent the valid re-use of a
      previously originated message to send to another destination
      party.

8.2.  Solution Considerations

   The use of PASSporT tokens based on the validation of the digital
   signature and the associated certificate requires consideration of
   the authentication and authority or reputation of the signer to
   attest to the identity being asserted.  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 identity being
   asserted.  It can and often is the case that the end user that the
   identity represents and signer are not one in the same.  However,
   applications that use PASSporT should ensure the signer is in an
   authoritative position to represent the user and authenticate the
   user onto the communications network and should be the responsible
   party for protecting the destination party from potential identity
   spoofing in addition to other abuse of the communications network
   outside of PASSporT.

8.3.  Privacy Considerations

   Because PASSporT explicitly includes claims of identifiers of parties
   involved in communications, date and times, and potentially other
   call detail, care should be taken outside of traditional protected or
   private telephony communications paths where there may be concerns
   about exposing information to either unintended or illegitimate
   actors.  These identifiers are often exposed through many
   communications signaling protocols as of today, but appropriate
   precautions should be taken.

9.  IANA Considerations

9.1.  Media Type Registration

9.1.1.  Media Type Registry Contents Additions Requested

   This section registers the "application/passport" media type
   [RFC2046] in the "Media Types" registry 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

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   o  Subtype name: passport

   o  Required parameters: n/a

   o  Optional parameters: n/a

   o  Encoding considerations: 8bit; application/passport values outside
      the US-ASCII range are encoded using percent encoding as described
      in section 2.1 of RFC 3986 (some values 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-05

   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

   o  Person and email address to contact for further information: Chris
      Wendt, chris-ietf@chriswendt.net

   o  Intended usage: COMMON

   o  Restrictions on usage: none

   o  Author: Chris Wendt, chris-ietf@chriswendt.net

   o  Change Controller: IESG

   o  Provisional registration?  No

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9.2.  JSON Web Token Claims Registration

9.2.1.  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-
      passport-05

   o  Claim Name: "dest"

   o  Claim Description: Destination Identity String

   o  Change Controller: IESG

   o  Specification Document(s): Section 3.2 of draft-ietf-stir-
      passport-05

   o  Claim Name: "mky"

   o  Claim Description: Media Key Fingerprint String

   o  Change Controller: IESG

   o  Specification Document(s): Section 3.2 of draft-ietf-stir-
      passport-05

10.  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, Eric Burger for
   their review, ideas, and contributions also thanks to Henning
   Schulzrinne, Russ Housley, Alan Johnston, Richard Barnes, Mark
   Miller, Ted Hardie, Dave Crocker, Robert Sparks for valuable feedback
   on the technical and security aspects of the document.  Additional
   thanks to Harsha Bellur for assistance in coding the example tokens.

11.  References

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11.1.  Normative References

   [I-D.ietf-stir-rfc4474bis]
              Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-12
              (work in progress), August 2016.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,
              <http://www.rfc-editor.org/info/rfc2046>.

   [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,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <http://www.rfc-editor.org/info/rfc4566>.

   [RFC4572]  Lennox, J., "Connection-Oriented Media Transport over the
              Transport Layer Security (TLS) Protocol in the Session
              Description Protocol (SDP)", RFC 4572,
              DOI 10.17487/RFC4572, July 2006,
              <http://www.rfc-editor.org/info/rfc4572>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <http://www.rfc-editor.org/info/rfc6838>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <http://www.rfc-editor.org/info/rfc7515>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <http://www.rfc-editor.org/info/rfc7518>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <http://www.rfc-editor.org/info/rfc7519>.

   [RFC7638]  Jones, M. and N. Sakimura, "JSON Web Key (JWK)
              Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
              2015, <http://www.rfc-editor.org/info/rfc7638>.

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11.2.  Informative References

   [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,
              <http://www.rfc-editor.org/info/rfc3261>.

   [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,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC7340]  Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
              Telephone Identity Problem Statement and Requirements",
              RFC 7340, DOI 10.17487/RFC7340, September 2014,
              <http://www.rfc-editor.org/info/rfc7340>.

Appendix A.  Example PASSporT JWS Serialization and Signature

   For PASSporT, there will always be a JWS with the following members:

   o  "protected", with the value BASE64URL(UTF8(JWS Protected Header))

   o  "payload", with the value BASE64URL (JWS Payload)

   o  "signature", with the value BASE64URL(JWS Signature)

   This example will follow the steps in JWS [RFC7515] Section 5.1,
   steps 1-6 and 8 and incorporates the additional serialization steps
   required for PASSporT.

   Step 1 for JWS references the JWS Payload, an example PASSporT
   Payload is as follows:

       {
           "dest":{"uri":["sip:alice@example.com"]}
           "iat":"1443208345",
           "orig":{"tn":"12155551212"}
       }

   This would be serialized to the form (with line break used for
   display purposes only):

       {"dest":{"uri":["sip:alice@example.com"]},"iat":"1443208345",
           "orig":{"tn":"12155551212"}}

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   Step 2 Computes the BASE64URL(JWS Payload) producing this value (with
   line break used for display purposes only):

       eyJkZXN0Ijp7InVyaSI6WyJzaXA6YWxpY2VAZXhhbXBsZS5jb20iXX0sImlhd
       CI6IjE0NDMyMDgzNDUiLCJvcmlnIjp7InRuIjoiMTIxNTU1NTEyMTIifX0

   For Step 3, an example PASSporT Protected Header comprising the JOSE
   Header is as follows:

       {
           "typ":"passport",
           "alg":"ES256",
           "x5u":"https://cert.example.org/passport.cer"
       }

   This would be serialized to the form (with line break used for
   display purposes only):

       {"alg":"ES256","typ":"passport","x5u":"https://cert.example.org/
           passport.cer"}

   Step 4 Performs the BASE64URL(UTF8(JWS Protected Header)) operation
   and encoding produces this value (with line break used for display
   purposes only):

       eyJhbGciOiJFUzI1NiIsInR5cCI6InBhc3Nwb3J0IiwieDV1IjoiaHR0cHM6Ly9j
       ZXJ0LmV4YW1wbGUub3JnL3Bhc3Nwb3J0LmNlciJ9

   Step 5 and Step 6 performs the computation of the digital signature
   of the PASSporT Signing Input ASCII(BASE64URL(UTF8(JWS Protected
   Header)) || '.' || BASE64URL(JWS Payload)) using ES256 as the
   algorithm and the BASE64URL(JWS Signature).

       rq3pjT1hoRwakEGjHCnWSwUnshd0-zJ6F1VOgFWSjHBr8Qjpjlk-cpFYpFYso
       jNCpTzO3QfPOlckGaS6hEck7w

   Step 8 describes how to create the final PASSporT token,
   concatenating the values in the order Header.Payload.Signature with
   period ('.') characters.  For the above example values this would
   produce the following (with line breaks between period used for
   readability purposes only):

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       eyJhbGciOiJFUzI1NiIsInR5cCI6InBhc3Nwb3J0IiwieDV1IjoiaHR0cHM6Ly
       9jZXJ0LmV4YW1wbGUub3JnL3Bhc3Nwb3J0LmNlciJ9
       .
       eyJkZXN0Ijp7InVyaSI6WyJzaXA6YWxpY2VAZXhhbXBsZS5jb20iXX0sImlhd
       CI6IjE0NDMyMDgzNDUiLCJvcmlnIjp7InRuIjoiMTIxNTU1NTEyMTIifX0
       .
       rq3pjT1hoRwakEGjHCnWSwUnshd0-zJ6F1VOgFWSjHBr8Qjpjlk-cpFYpFYso
       jNCpTzO3QfPOlckGaS6hEck7w

A.1.  X.509 Private Key Certificate for Example

       -----BEGIN EC PRIVATE KEY-----
       MHcCAQEEIFeZ1R208QCvcu5GuYyMfG4W7sH4m99/7eHSDLpdYllFoAoGCCqGSM49
       AwEHoUQDQgAE8HNbQd/TmvCKwPKHkMF9fScavGeH78YTU8qLS8I5HLHSSmlATLcs
       lQMhNC/OhlWBYC626nIlo7XeebYS7Sb37g==
       -----END EC PRIVATE KEY-----

A.2.  X.509 Public Key Certificate for Example

       -----BEGIN PUBLIC KEY-----
       MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8HNbQd/TmvCKwPKHkMF9fScavGeH
       78YTU8qLS8I5HLHSSmlATLcslQMhNC/OhlWBYC626nIlo7XeebYS7Sb37g==
       -----END PUBLIC KEY-----

Authors' Addresses

   Chris Wendt
   Comcast
   One Comcast Center
   Philadelphia, PA  19103
   USA

   Email: chris-ietf@chriswendt.net

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

   Email: jon.peterson@neustar.biz

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