Network Working Group                                        J. Peterson
Internet-Draft                                                   Neustar
Intended status: Informational                                  C. Wendt
Expires: May 4, 2017                                             Comcast
                                                        October 31, 2016

                   PASSporT Extension for Caller Name


   This document extends the PASSporT object, which conveys
   cryptographically-signed information about the people involved in
   personal communications, to include a human-readable display name
   comparable to the "Caller ID" function common on the telephone
   network.  The element defined for this purpose is extensible to
   include related information callers.

Status of This Memo

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   This Internet-Draft will expire on May 4, 2017.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  PASSporT 'cna' Claim  . . . . . . . . . . . . . . . . . . . .   3
   4.  Using 'cna' in SIP  . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Authentication Service Behavior . . . . . . . . . . . . .   4
     4.2.  Verification Service Behavior . . . . . . . . . . . . . .   4
   5.  Third Party Uses  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Further Information Associated with Callers . . . . . . . . .   6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  JSON Web Token Claims . . . . . . . . . . . . . . . . . .   6
     8.2.  PASSporT Types  . . . . . . . . . . . . . . . . . . . . .   6
     8.3.  PASSporT CNA Types  . . . . . . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. Informative References  . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   PASSporT [I-D.ietf-stir-passport] is a token format based on JWT
   [RFC7519] for conveying cryptographically-signed information about
   the people involved in personal communications; it is used with STIR
   [I-D.ietf-stir-rfc4474bis] to convey a signed assertion of the
   identity of the participants in real-time communications established
   via a protocol like SIP.  This specification extends PASSporT to
   carry the name of the person on one side of a communications session,
   along with related display information that would typically be
   rendered to the called party during alerting.  This format is
   designed to be extended with additional elements to convey richer

   In the traditional telephone network, the display name associated
   with a call is typically provided in one of three ways: by the
   originator of a call, by a third-party service queried by the
   terminating side, or through a local address book maintained by a
   device on the terminating side.  The STIR architecture lends itself
   especially to the first of these approaches, as it assumes that an
   authority on the originating side of the call provides a
   cryptographic assurance of the validity of the calling party number
   in order to prevent impersonation attacks.  That same authority could
   sign for a display name associated with that number, which the
   terminating side could render to the user when the call is alerting.
   But even when the originating side cannot provide a display name for

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   the caller, the cryptographic attestation of the validity of the
   number provided by STIR allows the terminating side to query a local
   or remote service for a name associated with that number without fear
   that the number has been impersonated.  This specification also
   outlines various ways that a display name for a calling party could
   be associated with a call on the terminating side in a secure

   The STIR problem statement [RFC7340] notes that securing the display
   name of callers is outside of STIR's immediate scope, so it includes
   no core feature for caller name.  This specification documents an
   optional extension to PASSporT and the associated STIR mechanisms to
   provide this function.

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
   described in RFC 2119 [RFC2119] and RFC 6919 [RFC6919].

3.  PASSporT 'cna' Claim

   This specification defines a new JSON Web Token claim for "cna",
   which provides a display name associated with the originator of
   personal communications.  This name may for example derive from the
   display-name component of the From header field value of a SIP
   request, or a similar field in other PASSporT using protocols.

   The "cna" claim may appear in the PASSporT claim as an optional
   element.  The creator of a PASSporT object can however add a "ppt"
   value of "cna" to the header of a PASSporT object as well, in which
   case the PASSporT claims MUST contain a "cna" claim, and any entities
   verifying the PASSporT object will be required to understand the
   "ppt" extension in order to process the PASSporT in question.  A
   header wih the "ppt" included will look as follows:

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

   The PASSporT claims object will then contain the "cna" key with its
   corresponding value.  The value of "cna" is an array of JSON objects,
   of which one, the "nam" object, is mandatory.  The key syntax of
   "nam" follows the display-name ABNF given in [RFC3261].

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      { "orig":{"tn":"12155551212"},
        "cna":{"nam":"Alice A"} }

   After the header and claims PASSporT objects have been constructed,
   their signature is generated normally per the guidance in

4.  Using 'cna' in SIP

   This section specifies SIP-specific usage for the "cna" claim in
   PASSporT, and in the SIP Identity header field value.  Other using
   protocols of PASSporT may define their own usages for the "cna"

4.1.  Authentication Service Behavior

   A PASSporT containing a "cna" claim may contain a "ppt" for "cna" or
   not.  If "ppt" does contain a "cna", then any SIP authentication
   services MUST add a "ppt" parameter to the Identity header containing
   that PASSporT with a value of "cna".  The resulting Identity header
   might look as follows:

  Identity: "sv5CTo05KqpSmtHt3dcEiO/1CWTSZtnG3iV+1nmurLXV/HmtyNS7Ltrg9dlxkWzo
      pPqOg1uXndzHbG7mR6Rl9BnUhHufVRbp51Mn3w0gfUs="; \

   Otherwise, there is no no need for the "ppt" parameter of the SIP
   Identity header.

   A SIP authentication service typically will derive the value of "cna"
   from the display-name component of the From header field value.  It
   is however a matter of authentication service policy to decide how it
   populates the value of "cna", which might also derive from other
   fields in the request, from customer profile data or from access to
   external services.  If the authentication service generates a
   PASSporT object containing "cna" with a value that is not equivalent
   to the From header field display-name value, it MUST use the full
   form of the PASSporT object.

4.2.  Verification Service Behavior

   [I-D.ietf-stir-rfc4474bis] Section 6.2 Step 5 requires that
   specifications defining "ppt" values describe any additional verifier
   behavior.  The behavior specified for the "ppt" values of "cna" is as
   follows.  If the PASSporT is in compact form, then the verification

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   service SHOULD extract the display-name from the From header field
   value, if any, and use that as the value for the "cna" key when it
   recomputes the header and claims of the PASSporT object.  If the
   signature validates over the recomputed object, then the verification
   should be considered successful.

   However, if the PASSport is in full form with a "ppt" value of "cna",
   then the verification service MUST extract the value associated with
   the "cna" "nam" key in the object.  If the signature validates, then
   the verification service can use the value of the "cna" "nam" key as
   the display name of calling party, which would in turn be rendered to
   alerted users or otherwise leveraged in accordance with local policy.
   This will allow SIP networks that convey the display name through a
   field other than the From header field to interoperate with this

   The behavior of a SIP UAS upon receiving an INVITE containing a
   PASSporT object with a "cna" claim will largely remain a matter of
   implementation policy.  In most cases, implementations would render
   this calling party name information to the user while alerting.  Any
   user interface additions to express confidence in the veracity of
   this information are outside the scope of this specification.

5.  Third Party Uses

   When calling name information cannot be provided on the originating
   side, a third-party information service may be queried by the
   terminating side with the calling party's number in order to learn
   the name of the calling party.  This query could come from an
   intermediary on the terminating side, or from the terminating user
   agent, such as a smart phone.

   An intermediary use case might look as follows: a SIP INVITE carries
   a display name in its From header field value and an initial PASSporT
   object without the "cna" claim.  When the terminating verification
   service receives this request, and determines that the signature is
   valid, it might query a third-party service that maps telephone
   numbers to calling party names.  Upon receiving the response, the
   terminating side could add a new Identity to the request (effectively
   acting as an authentication service) which contains a "cna" PASSporT
   object provided by the third-party service.  If the display name in
   the "cna" PASSporT object matches the display name in the INVITE,
   then the name would presumably be rendered to the end user by the
   terminating user agent.

   Alternatively, it might be the terminating user agent that queries a
   third-party service.  In this case, no new Identity header would be
   gneerated, though the terminating user agent might receive a PASSporT

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   object in return from the third-party service, and use the "cna"
   field in the object as a calling name to render to users during

   Detailed behavior for third-party uses is left for future versions of
   this specification.

6.  Further Information Associated with Callers

   Beyond naming information, there may be additional information about
   the calling party that should be rendered to the end user.  This may
   include information related to the location of the caller, or to any
   institutions that the caller is associated with, or even categories
   of institutions.  All of these data elements would benefit from the
   secure attestations provided by the STIR and PASSporT frameworks.
   The specification of the "cna" claim could entail the optional
   presence of one or more such additional information fields.

   A new IANA registry has been defined to hold potential values of the
   "cna" array; see Section 8.3.  Details of extensions to the "cna"
   claim to encompass other data elements are left for future version of
   this specification.

7.  Acknowledgments

   We would like to thank YOU for contributions to this problem
   statement and framework.

8.  IANA Considerations

8.1.  JSON Web Token Claims

   This specification requests that the IANA add a new claim to the JSON
   Web Token Claims registry as defined in [RFC7519].

   Claim Name: "cna"

   Claim Description: Caller Name Information

   Change Controller: IESG

   Specification Document(s): [RFCThis]

8.2.  PASSporT Types

   This specification requests that the IANA add a new entry to the
   PASSporT Types registry for the type "cna" which is specified in

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8.3.  PASSporT CNA Types

   This document requests that the IANA create a new registry for
   PASSporT CNA types.  Registration of new PASSporT CNA types shall be
   under the Specification Required policy.

   This registry is to be initially populated with a single value for
   "nam" which is specified in [RFCThis].

9.  Security Considerations


10.  Informative References

              Wendt, C. and J. Peterson, "Personal Assertion Token
              (PASSporT)", draft-ietf-stir-passport-09 (work in
              progress), October 2016.

              Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-14
              (work in progress), October 2016.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [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,

   [RFC6919]  Barnes, R., Kent, S., and E. Rescorla, "Further Key Words
              for Use in RFCs to Indicate Requirement Levels", RFC 6919,
              DOI 10.17487/RFC6919, April 2013,

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

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

Authors' Addresses

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


   Chris Wendt
   One Comcast Center
   Philadelphia, PA  19103


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