STIR                                                            C. Wendt
Internet-Draft                                                   Comcast
Intended status: Standards Track                             J. Peterson
Expires: February 23, 2017                                  Neustar Inc.
                                                         August 22, 2016

                        Persona Assertion Token


   This document defines a canonical string object or 'token' for
   verifying with non-repudiation the author of the token, their
   authority to author the token and, minimally, the asserted
   originating identity or persona contained within the token
   corresponding specifically to the originator of 'personal
   communications', or any signalled communications between a set of
   parties with identities.  A cryptographic signature is defined to
   protect the integrity of the information used to 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.  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 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
   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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 23, 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
   ( 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  PASSporT Token Overview . . . . . . . . . . . . . . . . . . .   3
   3.  PASSporT Components . . . . . . . . . . . . . . . . . . . . .   4
     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 Payload  . . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  JWT defined claims  . . . . . . . . . . . . . . . . .   5  "iat" - Issued At claim . . . . . . . . . . . . .   5
       3.2.2.  PASSporT specific claims  . . . . . . . . . . . . . .   5  Originating and Destination Identity Claims . . .   5  "mky" - Media Key claim . . . . . . . . . . . . .   7
     3.3.  PASSporT Signature  . . . . . . . . . . . . . . . . . . .   8
   4.  Extending PASSporT  . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  "ppt" (PASSporT) header parameter . . . . . . . . . . . .   8
     4.2.  Extended PASSporT Claims  . . . . . . . . . . . . . . . .   9
   5.  Deterministic JSON Serialization  . . . . . . . . . . . . . .   9
     5.1.  Example PASSport deterministic JSON form  . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
     6.1.  Avoidance of replay and cut and paste attacks . . . . . .  10
     6.2.  Solution Considerations . . . . . . . . . . . . . . . . .  10
     6.3.  Privacy Considerations  . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Media Type Registration . . . . . . . . . . . . . . . . .  11
       7.1.1.  Media Type Registry Contents Additions Requested  . .  11
     7.2.  JSON Web Token Claims Registration  . . . . . . . . . . .  12
       7.2.1.  Registry Contents Additions Requested . . . . . . . .  12
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13

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     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Appendix A.  Example PASSporT JWS Serialization and Signature . .  14
     A.1.  X.509 Private Key Certificate for Example . . . . . . . .  16
     A.2.  X.509 Public Key Certificate for Example  . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

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, 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.

   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

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

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   an associated digital signature using X.509 based certificates.  JWT
   provides a set of claims in JSON format that can conveniently
   accomidate 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.

3.  PASSporT Components

   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
   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.

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

3.1.1.  "typ" (Type) Header Parameter

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

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

3.1.2.  "alg" (Algorithm) Header Parameter

   For PASSporT, the "alg" should be defined as follows, for the
   creation and verification of PASSporT tokens and their digital
   signatures ES256 MUST be implemented.

   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.  Generally this would correspond to

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   an HTTPS or DNSSEC resource with the guidance that it MUST be TLS
   protected, per JWS spec.

   An example of the header, would be the following,


3.2.  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] and be encoded as defined by the
   JWS Payload [RFC7515].

   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

   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 of [RFC3986].  Matching of these values should
   use string exact match.

3.2.1.  JWT defined claims  "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.

3.2.2.  PASSporT specific claims  Originating and Destination Identity Claims

   PASSporT defines claims that convey the identity of the origination
   and destination of personal communications.  There are two claims
   that are required for PASSporT, the "orig" and "dest" claims.  Both
   "orig" and "dest" MUST have claims where the key represents an

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   identity type and the value is the identity string, both defined in
   subsecquent 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.  Additionaly, 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.  "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 7.2.  "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.  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.  Examples

   Single Originator, with telephone number identity +12155551212, to
   Single Destination, with URI identity '',

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   Single Originator, with telephone number identity +12155551212, to
   Multiple Destination Identities, with telephone number identity
   +12125551212 and two URI identities, and, example:

       }  "mky" - Media Key claim

   Some protocols that use PASSporT convey hashes for media security
   keys within their signaling in order to bind those keys to the
   identities established in the signaling layers.  One example would be
   the DTLS-SRTP key fingerprints carried in SDP [RFC4566] via the
   "a=fingerprint" attribute; multiple instances of that fingerprint may
   appear in a single SDP body corresponding to 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 is multiple fingerprint values, for example
   associated with different media streams in SDP, the fingerprint
   values MUST be constructed as a JSON array denoted by bracket

   For the 'dig' key value, the hash value MUST be the hexadecimal value
   without any colons.

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

   For an SDP offer that includes the following fingerprint values,

       a=fingerprint:sha-256 02:1A:CC:54:27:AB:EB:9C:53:3F:3E:4B:65:
       a=fingerprint:sha-256 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:

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   the PASSporT Payload object would be:


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.

4.  Extending PASSporT

   PASSporT includes the bare minimum set of claims needed to securely
   assert the originating identity and support the secure propoerties
   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.

4.1.  "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"
   hedaer 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

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4.2.  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.

5.  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 digitial
   signature verification work deterministically, the JSON
   representation of the PASSporT Header and Claims, particularly if
   PASSporT is used across multiple signaling environments, specifically
   the JSON header object and JSON Claim object MUST be computed as

   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.

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5.1.  Example PASSport deterministic JSON form

   For the example PASSporT Payload shown in Section, the
   following is the deterministic JSON object form.

       {"dest":{"uri":[""],"iat": 1443208345,"mky"

6.  Security Considerations

6.1.  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.
      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

6.2.  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 will be the case in
   telecommunications networks today, protecting the destination party
   from being spoofed may take some interpretation or additional
   verification of the link between the PASSporT signature and the
   persona being asserted.

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   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

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

6.3.  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.

7.  IANA Considerations

7.1.  Media Type Registration

7.1.1.  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

   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

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      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

   o  Intended usage: COMMON

   o  Restrictions on usage: none

   o  Author: Chris Wendt,

   o  Change Controller: IESG

   o  Provisional registration?  No

7.2.  JSON Web Token Claims Registration

7.2.1.  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-

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   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-

   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-

8.  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, and Ted Hardie for valuable feedback on the technical and
   security aspects of the document.  Additional thanks to Harsha Bellur
   for assistance in coding the example tokens.

9.  References

9.1.  Normative References

              Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-10
              (work in progress), July 2016.

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

   [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,

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   [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, <>.

   [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"",

9.2.  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,

   [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,

   [RFC7340]  Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
              Telephone Identity Problem Statement and Requirements",
              RFC 7340, DOI 10.17487/RFC7340, September 2014,

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))

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

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

   Note: there will never be a JWS Unprotected Header for PASSporT.

   First, an example PASSporT Protected Header is as follows:


   This would be serialized to the form:


   Encoding this with UTF8 and BASE64 encoding produces this value:


   Second, an example PASSporT Payload is as follows:


   This would be serialized to the form:


   Encoding this with the UTF8 and BASE64 encoding produces this value:


   Computing the digital signature of the PASSporT Signing Input
   ASCII(BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS


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   The final PASSporT token is produced by concatenating the values in
   the order Header.Payload.Signature with period (',') characters.  For
   the above example values this would produce the following:


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

       -----BEGIN EC PRIVATE KEY-----
       -----END EC PRIVATE KEY-----

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

       -----BEGIN PUBLIC KEY-----
       -----END PUBLIC KEY-----

Authors' Addresses

   Chris Wendt
   One Comcast Center
   Philadelphia, PA  19103


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


Wendt & Peterson        Expires February 23, 2017              [Page 16]