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

                        Persona Assertion Token


   This document defines a token format for verifying with non-
   repudiation the sender of and authorization to send information
   related to the originator of personal communications.  A
   cryptographic signature is defined to protect the integrity of the
   information used to identify the originator of a personal
   communications session (e.g. the telephone number or URI) and verify
   the accuracy of this 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 unsecure channel.  The Persona
   Assertion Token (PASSporT) is particularly useful for many personal
   communications applications over IP networks and other multi-hop
   interconnection scenarios where the originating and 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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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 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
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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.  Token Overview  . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  PASSporT Definition . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  PASSporT Header . . . . . . . . . . . . . . . . . . . . .   4
       3.1.1.  "typ" (Type) Header Parameter . . . . . . . . . . . .   4
       3.1.2.  "alg" (Algorithm) Header Parameter  . . . . . . . . .   5
       3.1.3.  "x5u" (X.509 URL) Header Parameter  . . . . . . . . .   5
     3.2.  PASSporT Payload  . . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  JWT defined claims  . . . . . . . . . . . . . . . . .   5  "iat" - Issued at claim . . . . . . . . . . . . .   5
       3.2.2.  PASSporT specific claims  . . . . . . . . . . . . . .   6  Originating and Destination Identity Claims . . .   6  "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.  Human Readability . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
     7.1.  Avoidance of replay and cut and paste attacks . . . . . .  10
     7.2.  Solution Considerations . . . . . . . . . . . . . . . . .  11
     7.3.  Privacy Considerations  . . . . . . . . . . . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Media Type Registration . . . . . . . . . . . . . . . . .  11
       8.1.1.  Media Type Registry Contents Additions Requested  . .  11
     8.2.  JSON Web Token Claims Registration  . . . . . . . . . . .  13
       8.2.1.  Registry Contents Additions Requested . . . . . . . .  13
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13

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     10.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Appendix A.  Example PASSporT JWS Serialization and Signature . .  15
     A.1.  X.509 Private Key Certificate for Example . . . . . . . .  16
     A.2.  X.509 Public Key Certificate for Example  . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

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 common method for creating and validating a
   token that cryptographically verifies an originating identity, or
   more generally a URI or application specific identity string
   representing the originator of personal communications.  Through
   extended profiles other information relevant to the personal
   communications can also be attached to the token.  The primary goal
   of PASSporT is to provide a common framework for signing persona
   related information in an extensible way.  A secondary goal is to
   provide this functionality independent of any specific personal
   communications signaling call logic, so that creation and
   verification of persona information can be implemented in a flexible
   way and can be used in many personal communications applications
   including end-to-end applications that require different signaling
   protocols.  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

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2.  Token Overview

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

3.  PASSporT Definition

   The PASSporT is constructed based on JWT [RFC7519] and JWS [RFC7515]
   specifications.  JWS defines the use of JSON data structures in a
   specified canonical format for signing data corresponding to JOSE
   header, JWS Payload, and JWS Signature.  JWT defines specific set of
   claims that are represented by specified key value pairs which can be
   extended with custom keys for specific applications.

3.1.  PASSporT Header

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

   An example of the header for the case of an ECDSA P-256 digital
   signature would be the following,


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 minimally include and begin
   with "passport".  This represents that the encoded token is a JWT of
   type passport.

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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.  Note: The definition of what the URI
   represents in terms of the actor serving the X.509 public key is out
   of scope of this document.  However, generally this would correspond
   to an HTTPS or DNSSEC resource with the guidance that it MUST be a
   TLS protected, per JWS spec.

3.2.  PASSporT Payload

   The token payload claims should consist of the information which
   needs to be verified at the destination party.  This claim should
   correspond to a JWT claim [RFC7519] and be encoded as defined by the
   JWS Payload [RFC7515]

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

   Key values outside the US-ASCII range should be encoded using percent
   encoding as described in section 2.1 of RFC 3986, 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] defined claim issued
   at.  As defined this should be set to a date cooresponding to 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

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   attacks, as explained further in the security considerations in
   section 7.

3.2.2.  PASSporT specific claims  Originating and Destination Identity Claims

   Baseline 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" should have values that are JSON
   objects that include identities represented by key value pairs, where
   the key represents an identity type and the value is the identity
   string.  Currently, these identities can be represented as either
   telephone numbers or Uniform Resource Indicators (URIs).  The
   definition of how telephone numbers or URIs and examples are provided

   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 should 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
   should 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" JSON

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   objects with "tn" and "uri" allow for other identity types with
   unique keys to represent these forms.  Examples

   Single Originator to Single Destination example:


   Single Originator to Multiple Destination Identities 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 via the "a=fingerprint"
   attribute; multiple instances of that fingerprint may appear in a
   single SDP body corresponding to difference media streams offered.
   The "mky" value of PASSporT contains a hexadecimal key presentation
   of any hash(es) necessary to establish media security via DTLS-SRTP.
   This mky value should be formated in a JSON form including the 'alg'
   and 'dig' keys with the corresponding algorithm and hexadecimal
   values.  Note that per guidance of Section 5 of this document any
   whitespace and line feeds must be removed.  If there is multiple
   fingerprint values, more than one, the fingerprint values should be
   constructed as a JSON array denoted by bracket characters.  For the
   'dig' key value, the hash value should be the hexadecimal value
   without any colons, in order to provide a more efficient, compact
   form to be encoded in PASSporT token claim.

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

   For an SDP offer that includes the following fingerprint values,

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       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:

   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 represents the bare minimum set of claims needed to assert
   the originating identity and support the secure propoerties discussed
   in various parts of this document, however there will certainly be
   both new uses and ways of extending the application and usage of
   PASSPorT that requires the ability to extend the defined base set of
   claims to represent other information requiring assertion or
   validation beyond the identity itself.

4.1.  "ppt" (PASSporT) header parameter

   For the extension of the base set of claims defined in this document,
   a new JWS header parameter "ppt" MUST be used with a string that
   uniquely identifies and points to a profile specification that
   defines any new claims that would extend the base set of claims of

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


4.2.  Extended PASSporT Claims

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

5.  Deterministic JSON Serialization

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

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

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

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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.  Human Readability

   JWT [RFC7519] and JWS [RFC7515] are defined to use Base64 and/or UTF8
   encoding to the Header, Payload, and Signature sections.  However,
   many personal communications protocols, such as SIP and XMPP, use a
   "human readable" format to allow for ease of use and ease of
   operational debugging and monitoring.  As such, specifications using
   PASSporT may provide guidance on whether Base64 encoding or plain
   text will be used for the construction of the PASSporT Header and
   Claim sections.

7.  Security Considerations

7.1.  Avoidance of replay and cut and paste attacks

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

   These would include:

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

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

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7.2.  Solution Considerations

   It should be recognized that the use of this token should not, in
   it's own right, be considered a full solution for absolute non-
   repudiation of the persona being asserted.  This only provides non-
   repudiation of the signer of PASSporT.  If the signer and the persona
   are not one in the same, which can and often 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.

   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

7.3.  Privacy Considerations

   Because PASSporT explicity includes claims of identitifiers of
   parties involved in communications, 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 illegitimately
   intented actors.  These identifiers are often exposed through many
   communications signaling protocols as of today, but appropriate
   precautions should be taken.

8.  IANA Considerations

8.1.  Media Type Registration

8.1.1.  Media Type Registry Contents Additions Requested

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

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   [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
      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

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8.2.  JSON Web Token Claims Registration

8.2.1.  Registry Contents Additions Requested

   o  Claim Name: "orig"

   o  Claim Description: Originating Identity String

   o  Change Controller: IESG

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

   o  Claim Name: "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-

9.  Acknowledgements

   Particular thanks to members of the ATIS and SIP Forum NNI Task Group
   including Jim McEchern, Martin Dolly, Richard Shockey, John Barnhill,
   Christer Holmberg, Victor Pascual Avila, Mary Barnes, 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.

10.  References

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10.1.  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,

   [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"",

10.2.  Informative References

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   [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))

   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:

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   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


   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-----

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Internet-Draft                  PASSporT                       July 2016

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


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