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RFC 8225 - PASSporT: Personal Assertion Token


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Internet Engineering Task Force (IETF)                          C. Wendt
Request for Comments: 8225                                       Comcast
Category: Standards Track                                    J. Peterson
ISSN: 2070-1721                                             Neustar Inc.
                                                           February 2018

                   PASSporT: Personal Assertion Token

Abstract

   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.  The Personal Assertion Token, PASSporT, is
   cryptographically signed to protect the integrity of the identity of
   the originator and to 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 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 Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8225.

Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) 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 ....................................................4
   2. Terminology .....................................................4
   3. PASSporT Overview ...............................................5
   4. PASSporT Header .................................................6
      4.1. "typ" (Type) Header Parameter ..............................6
      4.2. "alg" (Algorithm) Header Parameter .........................6
      4.3. "x5u" (X.509 URL) Header Parameter .........................6
      4.4. Example PASSporT Header ....................................7
   5. PASSporT Payload ................................................7
      5.1. JWT-Defined Claims .........................................7
           5.1.1. "iat" (Issued At) Claim .............................7
      5.2. PASSporT-Specific Claims ...................................8
           5.2.1. Originating and Destination Identity Claims .........8
           5.2.2. "mky" (Media Key) Claim ............................10
   6. PASSporT Signature .............................................11
   7. Compact Form of PASSporT .......................................12
      7.1. Example Compact Form of PASSporT ..........................13
   8. Extending PASSporT .............................................13
      8.1. "ppt" (PASSporT) Header Parameter .........................13
      8.2. Example Extended PASSporT Header ..........................14
      8.3. Extended PASSporT Claims ..................................14
   9. Deterministic JSON Serialization ...............................15
      9.1. Example PASSporT Deterministic JSON Form ..................16
   10. Security Considerations .......................................17
      10.1. Avoidance of Replay and Cut-and-Paste Attacks ............17
      10.2. Solution Considerations ..................................18
   11. IANA Considerations ...........................................18
      11.1. Media Type Registration ..................................18
      11.2. Registrations in "JSON Web Token Claims" .................19
      11.3. Registration in "JSON Web Signature and
            Encryption Header Parameters" ............................20
      11.4. PASSporT Extensions Registry .............................20
   12. References ....................................................20
      12.1. Normative References .....................................20
      12.2. Informative References ...................................22
   Appendix A. Example ES256-Based PASSporT JWS Serialization and
               Signature .............................................23
     A.1. X.509 Private Key in PKCS #8 Format for ES256 Example ......24
     A.2. X.509 Public Key for ES256 Example .........................25
   Acknowledgments ...................................................25
   Authors' Addresses ................................................25

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's telephone number for many
   legitimate purposes, including providing network features and
   services on 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
   into believing that 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 the extensions defined in Section 8
   of this document, 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 information related to
   the originating identity in an extensible way.  Additionally, this
   functionality is independent of any specific call logic for
   personal-communications signaling, so that the assertion of
   information related to the originating identity can be implemented in
   a flexible way and can be used in such applications as end-to-end
   applications that require different signaling protocols or gateways
   between different communications systems.  It is anticipated that
   guidance specific to the signaling protocol will be provided in other
   related documents and specifications to specify how to use and
   transport PASSporTs; however, this is intentionally out of scope for
   this document.

   [RFC8224] provides details of the use of PASSporT within the SIP
   [RFC3261] signaling protocol for the signing and verification of
   telephone numbers and SIP URIs.

2.  Terminology

   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
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  PASSporT Overview

   "JSON Web Token (JWT)" [RFC7519], "JSON Web Signature (JWS)"
   [RFC7515], and other 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 that are easily extensible for use in the 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 the JSON Object Signing and
   Encryption (JOSE) Header, JWS Payload, and JWS Signature.  JWT
   defines a set of claims that are represented by specified JSON
   objects that 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.

   PASSporT specifically uses this token format and defines claims that
   convey the identity of the origination and destination of personal
   communications.  The primary value asserted in a PASSporT object is
   the originating identity representing the identity of the calling
   party or the initiator of a personal-communications session.  The
   signer of a PASSporT object may or may not correspond to the
   originating identity.  For a given application's use or using
   protocol of PASSporT, the creation of the PASSporT object is
   performed by an entity that is authoritative to assert the caller's
   identity.  This authority is represented by the certificate
   credentials and the signature, and the PASSporT object is created and
   initiated to the destination(s) per the application's choice of
   authoritative point(s) in the network.  For example, the PASSporT
   object could be created 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 identities represent the
   intended destination of the personal communications, i.e., the
   identity(s) being called by the caller.  The destination point or
   points determined by the application need to have the capability to
   verify the PASSporT 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.

4.  PASSporT Header

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

   The PASSporT header should include, at a minimum, the Header
   Parameters defined in the next three subsections.

4.1.  "typ" (Type) Header Parameter

   The "typ" (Type) Header Parameter is defined in JWS ([RFC7515],
   Section 4.1.9) to declare the media type of the complete JWS.

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

4.2.  "alg" (Algorithm) Header Parameter

   The "alg" (Algorithm) Header Parameter is defined in JWS ([RFC7515],
   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],
   Section 3.1).

   For the creation and verification of PASSporTs and their digital
   signatures, implementations MUST support ES256 as defined in JWA
   ([RFC7518], Section 3.4).  Implementations MAY support other
   algorithms registered in the "JSON Web Signature and Encryption
   Algorithms" registry created by [RFC7518].  The contents of that
   registry may be updated in the future, depending on cryptographic
   strength requirements guided by current security best practices.  The
   mandatory-to-support algorithm for PASSporTs may likewise be updated
   in future updates to this document.

   Implementations of PASSporT digital signatures using ES256 as defined
   above SHOULD use the deterministic Elliptic Curve Digital Signature
   Algorithm (ECDSA) if or when supported for the reasons stated in
   [RFC6979].

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

   As defined in JWS ([RFC7515], 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 ([RFC7515], Section 4.1.5), this would correspond
   to an HTTPS or DNSSEC resource using integrity protection.

4.4.  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"
   }

5.  PASSporT Payload

   The token claims consist of the information that needs to be verified
   at the destination party.  These claims follow the definition of a
   JWT claim ([RFC7519], Section 4) and are 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.

   For PASSporT, any claim names MUST use the ASCII character set.  Any
   claim values can contain characters that are outside the ASCII range,
   consistent with the rules of creating a JWT Claims Set as defined in
   [RFC7519], Section 7.1.

5.1.  JWT-Defined Claims

5.1.1.  "iat" (Issued At) Claim

   The JSON claim MUST include the "iat" (Issued At) claim ([RFC7519],
   Section 4.1.6).  As defined, the "iat" claim should be set to the
   date and time of issuance of the JWT and MUST indicate the date and
   time of the origination of the personal communications.  The time
   value should be of the NumericDate format as defined in [RFC7519],
   Section 2.  This is included for securing the token against replay
   and cut-and-paste attacks, as explained further in Section 10
   ("Security Considerations").

5.2.  PASSporT-Specific Claims

5.2.1.  Originating and Destination Identity Claims

   The originating identity and the destination identity are represented
   by two claims that are required for PASSporT -- the "orig" and "dest"
   claims.  Both "orig" and "dest" MUST contain claim values that are
   identity claim JSON objects where the child claim name represents an
   identity type and the claim 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" claim is a JSON object with the claim name of "orig" and a
   claim value that is a JSON object representing the asserted identity
   of any type (currently either "tn" or "uri") of the originator of the
   personal-communications signaling.  There MUST be exactly one "orig"
   claim with exactly one identity claim object in a PASSporT object.

   Note: As explained in Section 3, the originating identity represents
   the calling party and may or may not correspond to the authoritative
   signer of the token.

   The "dest" claim is a JSON object with the claim name of "dest" and
   MUST have at least one identity claim object.  The "dest" claim value
   is an array containing one or more identity claim JSON objects
   representing the destination identities of any type (currently "tn"
   or "uri").  If the "dest" claim value array contains both "tn" and
   "uri" claim names, 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 in lexicographical order, including
   the scheme-specific portion of the URI characters.

   Note: As explained in Section 3, the destination identity represents
   the called party and may or may not correspond to the authoritative
   party verifying the token signature.

5.2.1.1.  "tn" (Telephone Number) Identity

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

   The claim value for the "tn" claim is the telephone number and MUST
   be canonicalized according to the procedures specified in [RFC8224],
   Section 8.3.

5.2.1.2.  "uri" (URI) Identity

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

5.2.1.3.  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.

5.2.1.4.  Examples

   The following is an example of a single originator with telephone
   number identity +12155551212, to a single destination with URI
   identity "sip:alice@example.com":

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

   The following is an example of a 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":

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

5.2.2.  "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" claim is an optional PASSporT claim defining the assertion of
   media key fingerprints carried in the Session Description Protocol
   (SDP) [RFC4566] via the "a=fingerprint" attribute ([RFC4572],
   Section 5).  This claim can support either a single fingerprint or
   multiple fingerprints appearing in a single SDP body corresponding to
   one or more media streams offered as defined in [RFC8122].

   The "mky" claim MUST be formatted as a JSON object with an array that
   includes the "alg" and "dig" claims with the corresponding algorithm
   and hexadecimal values.  If there is more than one fingerprint value
   associated with different media streams in SDP, the fingerprint
   values MUST be constructed as a JSON array denoted by square brackets
   ("[" and "]").  For the "dig" claim, the claim value MUST be the hash
   of the hexadecimal value without any colons.

   The "mky" claim is a JSON object with a claim name of "mky" and a
   claim value of a JSON array denoted by brackets.  The "mky" claim
   value JSON array MUST be constructed as follows:

   1.  Take each "a=fingerprint" line carried in the SDP.

   2.  Sort the lines based on the UTF-8 [RFC3629] encoding of the
       concatenation of the "alg" and "dig" claim value strings.

   3.  Encode the array in the order of the sorted lines, where each
       "mky" array element is a JSON object with two elements
       corresponding to the "alg" and "dig" objects, with "alg" first
       and "dig" second.

   An example claim with the "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:

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

6.  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, however, the lexicographic ordering and whitespace rules
   described in Sections 4 and 5 of this document, and the JSON
   serialization rules in Section 9 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.

   Step 7 of the JSON serialization procedure in [RFC7515], Section 5.1
   is not supported for PASSporT.

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

7.  Compact Form of PASSporT

   For a using protocol of PASSporT, the PASSporT claims as well as the
   PASSporT header may include redundant or default information that
   could be reconstructed at the destination based on information
   provided in the signaling protocol transporting the PASSporT object.
   In this case, it may be advantageous to have a more compact form of
   PASSporT to save the transmission of the bytes needed to represent
   the header and claims.

   This specification defines the compact form of the PASSporT, in the
   spirit of the form defined in [RFC7515], Appendix F, with the use of
   two periods ("..") to represent the header and claim objects being
   removed, followed by the PASSporT signature as defined in Section 6,
   and the need for the destination to reconstruct the header and claim
   objects in order to verify the signature.

   In order to construct the compact form of the PASSporT string, the
   procedure described in Section 6 MUST be used, with the exception of
   [RFC7515], Section 5.1, Step 8.  This step would be replaced by the
   following construction of the compact form of PASSporT, ".." ||
   BASE64URL(JWS Signature).

   The using protocol of the compact form of PASSporT MUST be
   accompanied by a specification for how the header and claims objects
   can be reconstructed from information in the signaling protocol being
   used.

   Note that the full form of the PASSporT, containing the entire
   header, payload, and signature, should also use the lexicographic
   ordering and whitespace serialization rules, particularly in the case
   where some using protocols or interworking between protocols may
   require switching between full and compact forms and maintaining the
   integrity of the signature.

7.1.  Example Compact Form of PASSporT

   The compact form of the following example token (with line breaks
   between periods used for readability purposes only)

   eyJhbGciOiJFUzI1NiIsInR5cCI6InBhc3Nwb3J0IiwieDV1IjoiaHR0cHM6Ly9j
   ZXJ0LmV4YW1wbGUub3JnL3Bhc3Nwb3J0LmNlciJ9
   .
   eyJkZXN0Ijp7InVyaSI6WyJzaXA6YWxpY2VAZXhhbXBsZS5jb20iXX0sImlhdCI
   6IjE0NDMyMDgzNDUiLCJvcmlnIjp7InRuIjoiMTIxNTU1NTEyMTIifX0
   .
   rq3pjT1hoRwakEGjHCnWSwUnshd0-zJ6F1VOgFWSjHBr8Qjpjlk-cpFYpFYsojN
   CpTzO3QfPOlckGaS6hEck7w

   would be as follows:

   ..rq3pjT1hoRwakEGjHCnWSwUnshd0-zJ6F1VOgFWSjHBr8Qjpjlk-cpFYpFYsojN
   CpTzO3QfPOlckGaS6hEck7w

8.  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
   straightforward way to add additional asserted or signed information
   by simply adding new claims.  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.

8.1.  "ppt" (PASSporT) Header Parameter

   Any using protocol can extend the payload of PASSporT with additional
   JWT claims.  JWT claims are managed by the "JSON Web Token Claims"
   IANA registry as defined in [RFC7519], Section 10.1.  Implementations
   of PASSporT MUST support the baseline claims defined in Section 5.2
   and MAY support extended claims.  If it is necessary for an extension
   to PASSporT to require that a relying party support a particular
   extended claim or set of claims in the PASSporT object, it can do so
   by specifying a "ppt" element for the PASSporT JOSE Header.  All
   values of "ppt" need to be defined in a specification that associates
   the new value of the "ppt" element with the required claims and
   behaviors.  Relying parties MUST fail to validate PASSporT objects
   containing an unsupported "ppt".

   Using protocols MUST explicitly define how they carry each claim and
   the rules for how the header and payload objects are constructed
   beyond the lexicographical and serialization rules defined in this
   document.

   Using protocols that carry the compact form of PASSporT (Section 7)
   instead of the full form MUST use only mandatory extensions signaled
   with "ppt" -- if a using protocol were to add additional optional
   claims to a PASSporT object it carried in compact form, relying
   parties would have no way to reconstruct the token.  Moreover, using
   protocols that support the compact form of PASSporT MUST have some
   field to signal "ppt" to relying parties, as the compact form of
   PASSporT omits the JOSE Header.

8.2.  Example Extended PASSporT Header

   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"
   }

8.3.  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 PASSporT claim elements
   specified in Section 5; claims may only be appended to the claims
   object specified; they can never be removed or reordered.  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 is
   optional.  The creator of a PASSporT object cannot assume that
   destination systems will understand any given extension.
   Verification of PASSporTs 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 5.2.1.4 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"}
   }

9.  Deterministic JSON Serialization

   JSON objects can include spaces and line breaks, and key value pairs
   can occur in any order.  It is therefore a non-deterministic string
   format.  In order to make the digital signature verification work
   deterministically, the JSON representation of the JWS Protected
   Header object and JWS Payload object MUST be computed as follows.

   The JSON object MUST follow the following rules.  These rules are
   based on the thumbprint of a JSON Web Key (JWK) as defined in
   Section 3 Step 1 of [RFC7638].

   1.  The JSON object MUST contain no whitespace or line breaks before
       or after any syntactic elements.

   2.  JSON objects MUST have the keys ordered lexicographically by the
       Unicode [UNICODE] code points of the member names.

   3.  JSON value literals MUST be lowercase.

   4.  JSON numbers are to be encoded as integers unless the field is
       defined to be encoded otherwise.

   5.  Encoding rules MUST be applied recursively to member values and
       array values.

   Note: For any PASSporT extension claims, member names within the
   scope of a JSON object MUST NOT be equal to other member names;
   otherwise, serialization will not be deterministic.

9.1.  Example PASSporT Deterministic JSON Form

   This section demonstrates the deterministic JSON serialization for
   the example PASSporT Payload shown in Section 5.2.1.4.

   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"
       }
     ],
   }

   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":"021ACC5427ABEB9C533F3E4B652E7D463F5442CD5
   4F17A03A27DF9B07F4619B2"},{"alg":"sha-256","dig":"4AADB9B13F82183B5
   40212DF3E5D496B19E57CAB3E4B652E7D463F5442CD54F1"}],
   "orig":{"tn":"12155551212"}}

10.  Security Considerations

10.1.  Avoidance of Replay and Cut-and-Paste Attacks

   There are a number of security considerations regarding the use of
   the token for the avoidance of replay and cut-and-paste attacks.
   PASSporTs SHOULD only be sent with application-level protocol
   information (e.g., for SIP, an INVITE as defined in [RFC3261])
   corresponding to the required fields in the token.  A unique set of
   token claims and token signature is constructed using the originating
   identity being asserted with the "orig" claim along with the
   following two claims:

   o  The "iat" claim should correspond to a date/time that 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.  Therefore,
      validation of the token should consider date and time correlation,
      which could be influenced by usage specific to the signaling
      protocol and by network time differences.

   o  The "dest" claim is included to further restrict the use of a
      valid PASSporT being sent as a replay attack to other destination
      parties.  The verification of the PASSporT at the destination
      should verify that the "dest" claim matches the destination party
      as the intended recipient of the message.

10.2.  Solution Considerations

   The use of PASSporTs 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.  The following considerations should be
   recognized when using PASSporT:

   o  The use of this token should not, in its own right, be considered
      a full solution for absolute non-repudiation of the identity being
      asserted.

   o  In many applications, the signer and the end user represented by
      the asserted identity may not be one and the same.  For example,
      when a service provider signs and validates the token on behalf of
      the user consuming the service, the provider MUST have an
      authenticated and secure relationship with the end user or the
      device initiating and terminating the communications signaling.

   o  Applications that use PASSporT should ensure that the verification
      of the signature includes a means for verifying that the signer is
      authoritative through the use of an application-specific or
      service-specific set of common trust anchors for the application.

11.  IANA Considerations

11.1.  Media Type Registration

   This section registers the "application/passport" media type (see
   [RFC2046] for the definition of "media type") in the "Media Types"
   registry in the manner described in [RFC6838], to indicate that the
   content is a PASSporT-defined JWT.

   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) separated by period (".") characters.

   o  Security considerations: See the Security Considerations section
      of [RFC7515].

   o  Interoperability considerations: N/A

   o  Published specification: RFC 8225

   o  Applications that use this media type: Secure Telephone Identity
      Revisited (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 & 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

11.2.  Registrations in "JSON Web Token Claims"

   Claim Name: "orig"
   Claim Description: Originating Identity String
   Change Controller: IESG
   Reference: Section 5.2.1 of RFC 8225

   Claim Name: "dest"
   Claim Description: Destination Identity String
   Change Controller: IESG
   Reference: Section 5.2.1 of RFC 8225

   Claim Name: "mky"
   Claim Description: Media Key Fingerprint String
   Change Controller: IESG
   Reference: Section 5.2.2 of RFC 8225

11.3.  Registration in "JSON Web Signature and Encryption Header
       Parameters"

   Header Parameter Name: "ppt"
   Header Parameter Description: PASSporT extension identifier
   Header Parameter Usage Location(s): JWS
   Change Controller: IESG
   Reference: Section 8.1 of RFC 8225

11.4.  PASSporT Extensions Registry

   The IANA has created a new PASSporT Type registry for "ppt" parameter
   values.  That parameter and its values are defined in Section 8.1.
   New registry entries must contain the name of the "ppt" parameter
   value and the specification in which the value is described.  The
   policy for this registry is Specification Required [RFC8126].

12.  References

12.1.  Normative References

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

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of
              ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629,
              November 2003, <https://www.rfc-editor.org/info/rfc3629>.

   [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,
              <https://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, <https://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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc6838>.

   [RFC6979]  Pornin, T., "Deterministic Usage of the Digital Signature
              Algorithm (DSA) and Elliptic Curve Digital Signature
              Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979,
              August 2013, <https://www.rfc-editor.org/info/rfc6979>.

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

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://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,
              <https://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, <https://www.rfc-editor.org/info/rfc7638>.

   [RFC8122]  Lennox, J. and C. Holmberg, "Connection-Oriented Media
              Transport over the Transport Layer Security (TLS) Protocol
              in the Session Description Protocol (SDP)", RFC 8122,
              DOI 10.17487/RFC8122, March 2017,
              <https://www.rfc-editor.org/info/rfc8122>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in
              RFC 2119 Key Words", BCP 14, RFC 8174,
              DOI 10.17487/RFC8174, May 2017,
              <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8224]  Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 8224,
              DOI 10.17487/RFC8224, February 2018,
              <https://www.rfc-editor.org/info/rfc8224>.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard",
              <http://www.unicode.org/versions/latest/>.

12.2.  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,
              <https://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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc7340>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Appendix A.  Example ES256-Based 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); it 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":1471375418,
     "orig":{"tn":"12155551212"}
   }

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

   {"dest":{"uri":["sip:alice@example.com"]},"iat":1471375418,
   "orig":{"tn":"12155551212"}}

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

   eyJkZXN0Ijp7InVyaSI6WyJzaXA6YWxpY2VAZXhhbXBsZS5jb20iXX0sImlhdCI
   6MTQ3MTM3NTQxOCwib3JpZyI6eyJ0biI6IjEyMTU1NTUxMjEyIn19

   For Step 3, an example PASSporT Protected Header constructed as a
   JOSE Header is as follows:

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

   This would be serialized to the following 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, producing this value (with line break used for display
   purposes only):

   eyJhbGciOiJFUzI1NiIsInR5cCI6InBhc3Nwb3J0IiwieDV1IjoiaHR0cHM6Ly9j
   ZXJ0LmV4YW1wbGUub3JnL3Bhc3Nwb3J0LmNlciJ9

   Steps 5 and 6 perform 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).

   VLBCIVDCaeK6M4hLJb6SHQvacAQVvoiiEOWQ_iUkqk79UD81fHQ0E1b3_GluIkb
   a7UWYRM47ZbNFdOJquE35cw

   Step 8 describes how to create the final PASSporT, 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 periods used for readability
   purposes only):

   eyJhbGciOiJFUzI1NiIsInR5cCI6InBhc3Nwb3J0IiwieDV1IjoiaHR0cHM6Ly9j
   ZXJ0LmV4YW1wbGUub3JnL3Bhc3Nwb3J0LmNlciJ9
   .
   eyJkZXN0Ijp7InVyaSI6WyJzaXA6YWxpY2VAZXhhbXBsZS5jb20iXX0sImlhdCI
   6MTQ3MTM3NTQxOCwib3JpZyI6eyJ0biI6IjEyMTU1NTUxMjEyIn19
   .
   VLBCIVDCaeK6M4hLJb6SHQvacAQVvoiiEOWQ_iUkqk79UD81fHQ0E1b3_GluIkb
   a7UWYRM47ZbNFdOJquE35cw

A.1.  X.509 Private Key in PKCS #8 Format for ES256 Example

   -----BEGIN PRIVATE KEY-----
   MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgi7q2TZvN9VDFg8Vy
   qCP06bETrR2v8MRvr89rn4i+UAahRANCAAQWfaj1HUETpoNCrOtp9KA8o0V79IuW
   ARKt9C1cFPkyd3FBP4SeiNZxQhDrD0tdBHls3/wFe8++K2FrPyQF9vuh
   -----END PRIVATE KEY-----

A.2.  X.509 Public Key for ES256 Example

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

Acknowledgments

   Particular thanks to members of the ATIS and SIP Forum NNI Task
   Group, including Jim McEachern, Martin Dolly, Richard Shockey, John
   Barnhill, Christer Holmberg, Victor Pascual Avila, Mary Barnes, and
   Eric Burger, for their review, ideas, and contributions.  Thanks also
   to Henning Schulzrinne, Russ Housley, Alan Johnston, Richard Barnes,
   Mark Miller, Ted Hardie, Dave Crocker, Robert Sparks, and Jim Schaad
   for valuable feedback on the technical and security aspects of the
   document.  Additional thanks to Harsha Bellur for assistance in
   coding the example tokens.

Authors' Addresses

   Chris Wendt
   Comcast
   One Comcast Center
   Philadelphia, PA  19103
   United States of America

   Email: chris-ietf@chriswendt.net

   Jon Peterson
   Neustar Inc.
   1800 Sutter St. Suite 570
   Concord, CA  94520
   United States of America

   Email: jon.peterson@neustar.biz

 

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