Network Working Group                                        J. Peterson
Internet-Draft                                                   Neustar
Intended status: Informational                                  C. Wendt
Expires: January 4, 2018                                         Comcast
                                                            July 3, 2017

                 PASSporT Extension for Rich Call Data


   This document extends PASSporT, a token for conveying
   cryptographically-signed information about personal communications,
   to include rich data that can be rendered to users, such as 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 calls that helps
   people decide whether to pick up the phone.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 4, 2018.

Copyright Notice

   Copyright (c) 2017 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

Peterson & Wendt         Expires January 4, 2018                [Page 1]

Internet-Draft              STIR Caller Name                   July 2017

   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 'rcd' Claim  . . . . . . . . . . . . . . . . . . . .   3
   4.  Further Information Associated with Callers . . . . . . . . .   4
   5.  Third-Party Uses  . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Signing as a Third Party  . . . . . . . . . . . . . . . .   6
   6.  Levels of Assurance . . . . . . . . . . . . . . . . . . . . .   6
   7.  Using 'rcd' in SIP  . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Authentication Service Behavior . . . . . . . . . . . . .   7
     7.2.  Verification Service Behavior . . . . . . . . . . . . . .   7
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  JSON Web Token Claims . . . . . . . . . . . . . . . . . .   8
     9.2.  PASSporT Types  . . . . . . . . . . . . . . . . . . . . .   9
     9.3.  PASSporT RCD Types  . . . . . . . . . . . . . . . . . . .   9
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   11. Informative References  . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

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: 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 be rendered to the called
   party during alerting, or potentially used by an automaton to
   determine whether and how to alert a called party.

   In the traditional telephone network, the display name associated
   with a call is typically provided in one of three ways: by a third-

Peterson & Wendt         Expires January 4, 2018                [Page 2]

Internet-Draft              STIR Caller Name                   July 2017

   party service queried at the terminating side, by the originator of
   the call, 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.  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 fashion.

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 'rcd' Claim

   This specification defines a new JSON Web Token claim for "rcd", Rich
   Call Data, the value of which is an array of JSON subelements.  The
   initial subelement defined here is a display name, "nam", associated
   with the originator of personal communications, which 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

   The "rcd" claim may appear in any PASSporT claims object as an
   optional element.  The creator of a PASSporT MAY however add a "ppt"
   value of "rcd" to the header of a PASSporT as well, in which case the
   PASSporT claims MUST contain a "rcd" 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":"" }

Peterson & Wendt         Expires January 4, 2018                [Page 3]

Internet-Draft              STIR Caller Name                   July 2017

   The PASSporT claims object will then contain the "rcd" key with its
   corresponding value.  The value of "rcd" 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.",
        "rcd":{"nam":"Alice Atlanta"} }

   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 is not limited to information about the
   caller, but includes information about the call itself, which may
   derive from analytics that determine based on call patterns or
   similar data if the call is likely to be one the called party wants
   to receive.  Such data 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 processed 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 "rcd" array; see
   Section 9.3.  Specific extensions to the "rcd" PASSporT claim are
   left for future specification.

Peterson & Wendt         Expires January 4, 2018                [Page 4]

Internet-Draft              STIR Caller Name                   July 2017

   While in the traditional telephone network, the business relationship
   between calling customers and their telephone service providers is
   the ultimate root of information about a calling party's name, some
   other forms of data like crowdsourced reputation scores might derive
   from third parties.  It is more likely that when those elements are
   present, they will be in a third-party "rcd" PASSporT.

5.  Third-Party Uses

   While rich data about the call can be provided by an originating
   authentication service, the terminating side or an intermediary in
   the call path could also acquire rich call data by querying a third-
   party service.  In telephone operations today, a third-party
   information service is commonly queried with the calling party's
   number in order to learn the name of the calling party, and
   potentially other helpful information could also be passed over that
   interface.  The value of using a PASSporT 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.  The manner in which third-
   party services are discovered is outside the scope of this document.

   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 "rcd" claim.  When the a terminating verification
   service implemented at a SIP proxy server 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 for the "rcd" PASSporT object provided by the third-party
   service.  It would then forward the INVITE to the terminating user
   agent.  If the display name in the "rcd" 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.

   A very similar flow could be followed by an intermediary closer to
   the origination of the call.  Presumably such a service could be
   implemented at an originating network in order to decouple the
   systems that sign for calling party numbers from the systems that
   provide rich data about calls.

   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

Peterson & Wendt         Expires January 4, 2018                [Page 5]

Internet-Draft              STIR Caller Name                   July 2017

   "rcd" field in the object as a calling name to render to users while

5.1.  Signing as a Third Party

   When a third party issues a PASSporT with an "rcd" claim, the
   PASSporT MUST contain the "rcd" "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 PASSporT.

   A PASSporT with a "ppt" of "rcd" 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.  Levels of Assurance

   As "rcd" can be provided by either first or third parties, relying
   parties could benefit from an additional claim that indicates the
   relationship of the attesting party to the caller.  Even in first
   party cases, this admits of some complexity: the Communications
   Service Provider (CSP) to which a number was assigned might in turn
   delegate the number to a reseller, who would then sell the number to
   an enterprise, in which case the CSP might have little insight into
   the caller's name.  In third party cases, a caller's name could
   derive from any number of data sources, on a spectrum between public
   data scraped from web searches to a direct business relationship to
   the caller.  As multiple PASSporTs can be associated with the same
   call, potentially a verification service could receive attestations
   of the caller name from multiple sources, which have different levels
   of granularity or accuracy.

   Therefore PASSporTs that carry "rcd" data SHOULD also carry an
   indication of the relationship of the generator of the PASSporT to
   the caller.  [TBD claim - take from SHAKEN?]

7.  Using 'rcd' in SIP

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

Peterson & Wendt         Expires January 4, 2018                [Page 6]

Internet-Draft              STIR Caller Name                   July 2017

7.1.  Authentication Service Behavior

   An authentication service creating a PASSporT containing a "rcd"
   claim MAY include a "ppt" for "rcd" or not.  Third-party
   authentication services following the behavior in Section 5.1 MUST
   include a "ppt" of "rcd".  If "ppt" does contain a "rcd", then any
   SIP authentication services MUST add a "ppt" parameter to the
   Identity header containing that PASSporT with a value of "rcd".  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 "rcd" 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 "rcd", 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 "rcd" 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.

7.2.  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 "rcd" is as
   follows.  If the PASSporT is in compact form, then the verification
   service SHOULD extract the display-name from the From header field
   value, if any, and use that as the value for the "rcd" 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 "rcd",
   then the verification service MUST extract the value associated with
   the "rcd" "nam" key in the object.  If the signature validates, then
   the verification service can use the value of the "rcd" "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

Peterson & Wendt         Expires January 4, 2018                [Page 7]

Internet-Draft              STIR Caller Name                   July 2017

   The third-party "rcd" PASSporT cases presents some new challenges, as
   an attacker could attempt to cut-and-paste such a third-party
   PASSporT into a SIP request in an effort to get the terminating user
   agent to render the display name or confidence values it contains to
   a call that should have no such assurance.  A third-party "rcd"
   PASSporT provides no assurance that the calling party number has not
   been spoofed: if it is carried in a SIP request, for example, then
   some other PASSporT in another Identity header field value would have
   to carry a PASSporT attesting that.  A verification service MUST
   determine that the calling party number shown in the "orig" of the
   "rcd" PASSporT corresponds to the calling party number of the call it
   has received, and that the "iat" field of the "rcd" PASSporT is
   within the date interval that the verification service would
   ordinarily accept for a PASSporT.

   Verification services may alter their authorization policies for the
   credentials accepted to sign PASSporTs when third parties generate
   PASSporT objects, per Section 5.1.  This may include accepting a
   valid signature over a PASSporT even if it is signed with a
   credential that does not attest authority over the identity in the
   "orig" claim of the PASSporT, provided that the verification service
   has some other reason to trust the signer.  No further guidance on
   verification service authorization policy is given here.

   The behavior of a SIP UAS upon receiving an INVITE containing a
   PASSporT object with a "rcd" 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.

8.  Acknowledgments

   We would like to thank Robert Sparks for helpful suggestions.

9.  IANA Considerations

9.1.  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: "rcd"

   Claim Description: Caller Name Information

   Change Controller: IESG

Peterson & Wendt         Expires January 4, 2018                [Page 8]

Internet-Draft              STIR Caller Name                   July 2017

   Specification Document(s): [RFCThis]

9.2.  PASSporT Types

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

9.3.  PASSporT RCD Types

   This document requests that the IANA create a new registry for
   PASSporT RCD types.  Registration of new PASSporT RCD 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].

10.  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.

11.  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-02 (work in progress), June 2017.

Peterson & Wendt         Expires January 4, 2018                [Page 9]

Internet-Draft              STIR Caller Name                   July 2017

   [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


Peterson & Wendt         Expires January 4, 2018               [Page 10]