Network Working Group                                        J. Peterson
Internet-Draft                                                   Neustar
Intended status: Informational                                  C. Wendt
Expires: December 14, 2017                                       Comcast
                                                           June 12, 2017

                   PASSporT Extension for Caller Name


   This document extends PASSporT, a token for conveying
   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 about callers that helps people decide
   whether to pick up the phone.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on December 14, 2017.

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   document authors.  All rights reserved.

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

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.  The STIR problem statement [RFC7340]
   declared securing the display name of callers outside of STIR's
   initial scope, so baseline STIR provides no features for caller name.
   This specification documents an optional mechanism for PASSporT and
   the associated STIR mechanisms which extends PASSporT to carry
   additional elements conveying richer information, provided it is
   information that is intended to be rendered to an end user to assist
   a called party in determining whether to accept or trust incoming
   communications.  This includes the name of the person on one side of
   a communications session, the traditional "Caller ID" of the
   telephone network, along with related display information that would
   typically be rendered to the called party during alerting.

   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 at the
   terminating side, or through a local address book maintained by a

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   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.
   Even when the originating side does not provide a display name for
   the caller, the cryptographic attestation of the validity of the
   calling number provided by STIR still 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 by the
   caller; STIR thus makes "Caller ID" more secure even when there is no
   first-party attestation of a display name.  For these cases, this
   specification outlines various ways that a display name for a calling
   party could be determined at the terminating side in a secure

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", the
   value of which is an array of JSON elements which always includes 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 any PASSporT claims object as an
   optional element.  The creator of a PASSporT MAY 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
   PASSporT header wih the "ppt" included will look as follows:

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

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   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].

      { "orig":{"tn":"12155551212"},
            "iss":"Example, Inc.",
        "cna":{"nam":"Alice A"} }

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

4.  Further Information Associated with Callers

   Beyond naming information, there may be additional human-readable
   information about the calling party that should be rendered to the
   end user in order to help the called party decide whether or not to
   pick up the phone.  This could include:

      information related to the location of the caller, or

      any organizations or institutions that the caller is associated
      with, or even categories of institutions (is this a government
      agency, or a bank, or what have you), or

      hyperlinks to images, such as logos or pictures of faces, or to
      similar external profile information, or

      information that will be process by an application before
      rendering it to a user, like social networking data that shows
      that an unknown caller is a friend-of-a-friend, or reputation
      scores derived from crowdsourcing, or confidence scores based on
      broader analytics about the caller and callee.

   All of these data elements would benefit from the secure attestations
   provided by the STIR and PASSporT frameworks.  A new IANA registry
   has been defined to hold potential values of the "cna" array; see
   Section 8.3.  Specific extensions to the "cna" PASSporT claim are
   left for future specification.

   While in the telephone network, information about the name of the
   calling party traditionally derives from the originating service
   provider, some other forms of data like crowdsourced reputation
   scores might derive from third parties.  It is more likely that when

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   those elements are present, they will be in a third-party "cna"
   object, which requires special signing rules.

5.  Third Party Uses

   When secure calling name information is not provided by an
   originating authentication service, the terminating side may use
   other means to determine the caller's name.  For example, a third-
   party information service might be queried with the calling party's
   number in order to learn the name of the calling party and other
   helpful information.  This query could come from an intermediary, or
   from an end user device, such as a smart phone.  The value of using
   the PASSporT object to convey this information from third parties
   lies largely in the preservation of the original authority's
   signature over the data, and the potential for the PASSporT to be
   conveyed from intermediaries to endpoint devices.  Effectively, these
   use cases form of subcase of out-of-band [I-D.rescorla-stir-fallback]
   use cases.

   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 PASSport in a
   response from that third-party service, the terminating side could
   add a new Identity header field 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.

   In an alternative use case, the terminating user agent might query a
   third-party service.  In this case, no new Identity header field
   would be generated, though the terminating user agent might receive a
   PASSporT object in return from the third-party service, and use the
   "cna" field in the object as a calling name to render to users while

5.1.  Signing as a Third Party

   A third-party PASSporT MUST contain the "cna" "ppt" type in its
   header object.  It moreover MUST include an "iss" claim as defined in
   [RFC7519] to indicate the source of this PASSporT; that field SHOULD
   be populated with the subject of the credential used to sign the

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   A PASSporT with a "ppt" and "cna" MAY be signed with credentials that
   do not have authority over the identity that appears in the "orig"
   element of the PASSporT claims.  Relying parties in STIR have always
   been left to make their own authorization decisions about whether or
   not the trust the signers of PASSporTs, and in the third-party case,
   where an entity has explicitly queried a service to acquire the
   PASSporT object, it may be some external trust or business
   relationship that induces the relying party to trust a PASSporT.

6.  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"

6.1.  Authentication Service Behavior

   An authentication service creating a PASSporT containing a "cna"
   claim MAY include a "ppt" for "cna" or not.  Third party
   authentication services as described in Section 5.1 MUST include a
   "ppt" of "cna".  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="; \

   This specification assumes that by default, a SIP authentication
   service will derive the value of "cna" from the display-name
   component of the From header field value of the request.  It is
   however a matter of authentication service policy to decide how it
   populates the value of "cna", which MAY 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 in SIP.

6.2.  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

   Verification services may alter their authorization policies for the
   credentials accepted to sign PASSporTs when third parties generate
   PASSporT objects, per Section 5.1.  No guidance on verification
   service policy is given here.

   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.

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]

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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

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

   Revealing information such as the name, location, and affiliation of
   a person necessarily entails certain privacy risks.  Baseline
   PASSporT has no particular confidentiality requirement, as the
   information it signs over in a using protocol like SIP is all
   information that SIP carries in the clear anyway.  Transport-level
   security can hide those SIP fields from eavesdroppers, and the same
   confidentiality mechanisms would protect any PASSporT(s) carried in

   More TBD.

10.  Informative References

              Wendt, C. and J. Peterson, "Personal Assertion Token
              (PASSporT)", draft-ietf-stir-passport-11 (work in
              progress), February 2017.

              Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-16
              (work in progress), February 2017.

              Rescorla, E. and J. Peterson, "STIR Out of Band
              Architecture and Use Cases", draft-rescorla-stir-
              fallback-01 (work in progress), October 2016.

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   [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,

   [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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