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PASSporT Extension for Rich Call Data
draft-ietf-stir-passport-rcd-17

Document Type Active Internet-Draft (stir WG)
Authors Chris Wendt , Jon Peterson
Last updated 2022-05-10 (Latest revision 2022-04-25)
Replaces draft-peterson-stir-cnam
Stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
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Stream WG state In WG Last Call
Revised I-D Needed - Issue raised by WGLC, Doc Shepherd Follow-up Underway
Associated WG milestone
Nov 2019
Submit PASSPorT Extension for rich call data for publication as Proposed Standard
Document shepherd Russ Housley
IESG IESG state I-D Exists
Consensus boilerplate Yes
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Responsible AD (None)
Send notices to housley@vigilsec.com
draft-ietf-stir-passport-rcd-17
Network Working Group                                           C. Wendt
Internet-Draft                                                Somos Inc.
Intended status: Standards Track                             J. Peterson
Expires: 26 October 2022                                    Neustar Inc.
                                                           24 April 2022

                 PASSporT Extension for Rich Call Data
                    draft-ietf-stir-passport-rcd-17

Abstract

   This document extends PASSporT, a token for conveying
   cryptographically-signed call information about personal
   communications, to include rich meta-data about a call and caller
   that can be signed and integrity protected, transmitted, and
   subsequently rendered to the called party.  This framework is
   intended to include and extend caller and call specific information
   beyond human-readable display name comparable to the "Caller ID"
   function common on the telephone network.  The JSON element defined
   for this purpose, Rich Call Data (RCD), is an extensible object
   defined to either be used as part of STIR or with SIP Call-Info to
   include related information about calls that helps people decide
   whether to answer an incoming set of communications from another
   party.  This signing of the RCD information is also enhanced with a
   integrity mechanism that is designed to protect the authoring and
   transport of this information between authoritative and non-
   authoritative parties generating and signing the Rich Call Data for
   support of different usage and content policies.

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 https://datatracker.ietf.org/drafts/current/.

   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 26 October 2022.

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Copyright Notice

   Copyright (c) 2022 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 (https://trustee.ietf.org/
   license-info) 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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Overview of the use of the Rich Call Data PASSporT
           extension . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Overview of Rich Call Data Integrity  . . . . . . . . . . . .   5
   5.  PASSporT Claim "rcd" Definition and Usage . . . . . . . . . .   7
     5.1.  PASSporT "rcd" Claim  . . . . . . . . . . . . . . . . . .   7
       5.1.1.  "nam" key . . . . . . . . . . . . . . . . . . . . . .   7
       5.1.2.  "apn" key . . . . . . . . . . . . . . . . . . . . . .   7
       5.1.3.  "icn" key . . . . . . . . . . . . . . . . . . . . . .   8
       5.1.4.  "jcd" key . . . . . . . . . . . . . . . . . . . . . .   9
       5.1.5.  "jcl" key . . . . . . . . . . . . . . . . . . . . . .   9
   6.  "rcdi" RCD Integrity Claim Definition and Usage . . . . . . .  10
     6.1.  Creation of the "rcd" element digests . . . . . . . . . .  11
       6.1.1.  "nam" and "apn" elements  . . . . . . . . . . . . . .  12
       6.1.2.  "icn" elements  . . . . . . . . . . . . . . . . . . .  12
       6.1.3.  "jcd" elements  . . . . . . . . . . . . . . . . . . .  12
       6.1.4.  "jcl" elements  . . . . . . . . . . . . . . . . . . .  14
     6.2.  JWT Claim Constraints for "rcd" claims only . . . . . . .  15
   7.  JWT Claim Constraints usage for "rcd" and "rcdi" claims . . .  15
   8.  PASSporT "crn" claim - Call Reason Definition and Usage . . .  16
     8.1.  JWT Constraint for "crn" claim  . . . . . . . . . . . . .  16
   9.  Rich Call Data Claims Usage Rules . . . . . . . . . . . . . .  17
     9.1.  "rcd" PASSporT Verification . . . . . . . . . . . . . . .  17
     9.2.  "rcdi" Integrity Verification . . . . . . . . . . . . . .  18
     9.3.  Example "rcd" PASSporTs . . . . . . . . . . . . . . . . .  18
   10. Compact form of "rcd" PASSporT  . . . . . . . . . . . . . . .  20
     10.1.  Compact form of the "rcd" PASSporT claim . . . . . . . .  20
     10.2.  Compact form of the "rcdi" PASSporT claim  . . . . . . .  21
     10.3.  Compact form of the "crn" PASSporT claim . . . . . . . .  21
   11. Further Information Associated with Callers . . . . . . . . .  21
   12. Third-Party Uses  . . . . . . . . . . . . . . . . . . . . . .  22

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     12.1.  Signing as a Third Party . . . . . . . . . . . . . . . .  23
   13. Levels of Assurance . . . . . . . . . . . . . . . . . . . . .  24
   14. Using "rcd" in SIP  . . . . . . . . . . . . . . . . . . . . .  24
     14.1.  Authentication Service Behavior  . . . . . . . . . . . .  24
     14.2.  Verification Service Behavior  . . . . . . . . . . . . .  25
   15. Using "rcd" and "rcdi" as additional claims to other PASSporT
           extensions  . . . . . . . . . . . . . . . . . . . . . . .  26
     15.1.  Procedures for applying "rcd" as claims only . . . . . .  27
     15.2.  Example for applying "rcd" as claims only  . . . . . . .  27
   16. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  28
   17. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
     17.1.  JSON Web Token Claim . . . . . . . . . . . . . . . . . .  28
     17.2.  PASSporT Types . . . . . . . . . . . . . . . . . . . . .  29
     17.3.  PASSporT RCD Types . . . . . . . . . . . . . . . . . . .  29
   18. Security Considerations . . . . . . . . . . . . . . . . . . .  29
     18.1.  The use of JWT Claim Constraints in delegate certificates
            to exclude unauthorized claims . . . . . . . . . . . . .  30
   19. References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     19.1.  Normative References . . . . . . . . . . . . . . . . . .  30
     19.2.  Informative References . . . . . . . . . . . . . . . . .  32
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Introduction

   PASSporT [RFC8225] is a token format based on JWT [RFC7519] for
   conveying cryptographically-signed information about the parties
   involved in personal communications; it is used to convey a signed
   assertion of the identity of the participants in real-time
   communications established via a protocol like SIP [RFC8224].  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 procedures
   which extend PASSporT objects to protect additional elements
   conveying richer information: information that is intended to be
   rendered to assist a called party in determining whether to accept or
   trust incoming communications.  This includes the name of the person
   or entity 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.

   Traditional telephone network signaling protocols have long supported
   delivering a 'calling name' from the originating side, though in
   practice, the terminating side is often left to derive a name from
   the calling party number by consulting a local address book or an
   external database.  SIP similarly can carry this information in a

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   'display-name' in the From header field value from the originating to
   terminating side, or alternatively in the Call-Info header field.
   However, both are unsecured fields that really cannot be trusted in
   most interconnected SIP deployments, and therefore is a good starting
   point for a framework that utilizes STIR techniques and procedures
   for protecting call related information including but not limited to
   calling name.

   As such, the baseline use-case for this document extends PASSporT to
   provide cryptographic protection for the "display-name" field of SIP
   requests as well as further "rich call data" (RCD) about the caller,
   which includes the contents of the Call-Info header field or other
   data structures that can be added to the PASSporT.  This document
   furthermore specifies a third-party profile that would allow external
   authorities to convey rich information associated with a calling
   number via a new type of PASSporT.  Finally, this document describes
   how to preserve the integrity of the RCD in scenarios where there may
   be non-authoritative users initiating and signing RCD and therefore a
   constraint on the RCD data that a PASSporT can attest via
   certificate-level controls.

2.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Overview of the use of the Rich Call Data PASSporT extension

   The main intended use of the signing of Rich Call Data (RCD) using
   STIR within SIP [RFC8224] or more generally as a PASSporT extension
   [RFC8225] is for the entity that originates a call, either directly
   the caller themselves, if they are authoritative, or a service
   provider or third-party service that may be authoritative over the
   rich call data on behalf of the caller.

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   The RCD associated with the identity of the calling party described
   in this document is of two main categories.  The first data is a more
   traditional set of info about a caller associated with "display-name"
   in SIP [RFC3261], typically a textual description of the caller, or
   alternate presentation numbers often used in From Header field
   [RFC3261] or P-Asserted-ID [RFC3325].  The second category is a set
   of RCD that is defined as part of the jCard definitions or extensions
   to that data.  [I-D.ietf-sipcore-callinfo-rcd] describes the optional
   use of jCard in Call-Info header field as RCD with the "jcard" Call-
   Info purpose token.  Either or both of these two types of data can be
   incorporated into an "rcd" claim defined in this document.

   Additionally, in relation to the description of the specific
   communications event itself (versus the identity description in
   previous paragraph), [I-D.ietf-sipcore-callinfo-rcd] also describes a
   "call-reason" parameter intended for description of the intent or
   reason for a particular call.  A new PASSporT claim "crn", or call
   reason, can contain the string or object that describes the intent of
   the call.  This claim is intentionally kept separate from the "rcd"
   claim because it is envisioned that call reason is not the same as
   information associated with the caller and may change on a more
   frequent, per call, type of basis.

4.  Overview of Rich Call Data Integrity

   When incorporating call data that represents a user, even in
   traditional calling name services today, often there is policy and
   restrictions around what data is allowed to be used.  Whether
   preventing offensive language or icons or enforcing uniqueness,
   potential trademark or copyright violations or other policy
   enforcement, there might be the desire to pre-certify or "vet" the
   specific use of rich call data.  This document defines a mechanism
   that allows for a direct or indirect party that controls the policy
   to approve or certify the content, create a cryptographic digest that
   can be used to validate that data and applies a constraint in the
   certificate to allow the recipient and verifier to validate that the
   specific content of the RCD is as intended at its creation and
   approval or certification.

   There are two mechanisms that are defined to accomplish that for two
   distinct categories of purposes.  The first of the mechanisms include
   the definition of an integrity claim.  The RCD integrity mechanism is
   a process of generating a sufficiently strong cryptographic digest
   for each resource referenced by a URI within a claim value (e.g., an
   image file referenced by "jcd" or a jCard referenced by "jcl").  This
   mechanism is inspired by and based on the W3C Subresource Integrity
   specification (http://www.w3.org/TR/SRI/).  The second of the
   mechanisms uses the capability called JWT Claim Constraints, defined

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   in [RFC8226] and extended in [RFC9118].  The JWT Claim Constraints
   specifically guide the verifier within the certificate used to sign
   the PASSporT for the inclusion (or exclusion) of specific claims and
   their values, so that the content intended by the signer can be
   verified to be accurate.

   Both of these mechanisms, integrity digests and JWT Claims
   Constraints, can be used together or separately depending on the
   intended purpose.  The first category of purpose is whether the rich
   call data conveyed by the RCD passport is pass-by-value or passed-by-
   reference; i.e., is the information contained in the passport claims
   and therefore integrity protected by the passport signature, or is
   the information contained in an external resource referenced by a URI
   in the RCD PASSporT.  The second category of purpose is whether the
   signer is authoritative or has responsibility for the accuracy of the
   RCD based on the policies of the eco-system the RCD PASSporTs are
   being used.

   The following table provides an overview of the framework for how
   integrity should be used with RCD.  (Auth represents authoritative in
   this table)

   +----------+---------------------+--------------------------------+
   |   Modes  |  No external URIs   |      Includes URI refs         |
   +----------+---------------------+--------------------------------+
   |   Auth   | 1: No integrity req | 2: RDC Integrity               |
   +----------+---------------------+--------------------------------+
   | Non-Auth | 3: JWT Claim Const. | 4: RCD Integ./JWT Claim Const. |
   +----------+---------------------+--------------------------------+

   The first and simplest mode is exclusively for when all RCD content
   is directly included as part of the claims (i.e. no external
   reference URIs are included in the content) and when the signer is
   authoritative over the content.  In this mode, integrity protection
   is not required and the set of claims is simply protected by the
   signature of the standard PASSporT [RFC8225] and SIP identity header
   [RFC8224] procedures.  The second mode is an extension of the first
   where the signer is authoritative and an "rcd" claim contents include
   a URI identifying external resources.  In this mode, an RCD Integrity
   or "rcdi" claim MUST be included.  This integrity claim is defined
   later in this document and provides a digest of the "rcd" claim
   content so that, particularly for the case where there are URI
   references in the RCD, the content of that RCD can be comprehensively
   validated that it was received as intended by the signer of the
   PASSporT.

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   The third and fourth mode cover cases where there is a different
   authoritative entity responsible for the content of the RCD, separate
   from the signer of the PASSporT itself, allowing the ability to have
   forward control at the time of the creation of the certificate of the
   allowed or vetted content included in or referenced by the RCD claim
   contents.  The primary framework for allowing the separation of
   authority and the signing of PASSporTs by non-authorized entities is
   detailed in [RFC9060] although other cases may apply.  As with the
   first and second modes, the third and fourth modes differ with the
   absence or inclusion of externally referenced content using URIs.

5.  PASSporT Claim "rcd" Definition and Usage

5.1.  PASSporT "rcd" Claim

   This specification defines a new JSON Web Token claim for "rcd", Rich
   Call Data, the value of which is a JSON object that can contain one
   or more key value pairs.  This document defines a default set of key
   values.

5.1.1.  "nam" key

   The "nam" key value is a display name, 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 alternatively from the P-Asserted-Identity header field
   value, or a similar field in other PASSporT using protocols.  This
   key MUST be included once as part of the "rcd" claim value JSON
   object.  If there is no string associated with a display name, the
   claim value MUST then be an empty string.

5.1.2.  "apn" key

   The "apn" key value is an optional alternate presentation number
   associated with the originator of personal communications, which may
   for example derive from the user component of the From header field
   value of a SIP request (in cases where a network number is carried in
   the P-Asserted-Identity [RFC3325]), or alternatively from the
   Additional-Identity header field value [3GPP TS 24.229 v16.7.0], or a
   similar field in other PASSporT using protocols.  Its intended
   semantics are to convey a number that the originating user is
   authorized to show to called parties in lieu of their default number,
   such as cases where a remote call agent uses the main number of a
   call center instead of their personal telephone number.  The "apn"
   key value is a canonicalized telephone number per [RFC8224]
   Section 8.3.  If present, this key MUST be included once as part of
   the "rcd" claim value JSON object.

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   The use of the optional "apn" key is intended for cases where the
   signer of an rcd PASSporT authorizes the use of an alternate
   presentation number by the user.  How the signer determines that a
   user is authorized to present the number in question is a policy
   decision outside the scope of this document, however, the vetting of
   the alternate presentation number should follow the same level of
   vetting as telephone identities or any other information contained in
   an RCD PASSporT.  This usage is intended as an alternative to
   conveying the presentation number in the "tel" key value of a jCard,
   in situations where no other rich jCard data needs to be conveyed
   with the call.  Only one "apn" key may be present. "apn" MUST be used
   when it is the intent of the caller or signer to display the
   alternate presentation number even if "jcd" or "jcl" keys are present
   in a PASSporT with a "tel" key value.

5.1.3.  "icn" key

   The "icn" key value is an optional URI reference to an image that can
   be used to pictorially represent the originator of personal
   communications.  This icon key value should be used as a base or
   default method of associating an image with a calling party.

   When being used for SIP [RFC3261] this claim key value used to
   protect the call-info header field with a purpose parameter value of
   "icon" as described in Section 20.9 [RFC3261].  Example as follows:

   Call-Info: <http://wwww.example.com/alice/photo.jpg>;
     purpose=icon

   Note that [I-D.ietf-sipcore-callinfo-rcd] extends the specific usage
   of "icon" in SIP in the context of the larger rich call data
   framework with specific guidance on referencing images and image
   types, sizes and formats.

   It should be also noted that with jCard, as described in the
   following "jcd" and "jcl" key value sections and in
   [I-D.ietf-sipcore-callinfo-rcd], there are alternative ways of
   including photos and logos as URI references.  The "icn" key should
   be then considered a base or default image and jCard usage should be
   considered for profiles and extensions that provide more direct
   guidance on the usage of specific defined usage of what each image
   type represents for the proper rendering to end users.

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5.1.4.  "jcd" key

   The "jcd" key value is defined to contain a jCard [RFC7095] JSON
   object.  This jCard object is intended to represent and derives from
   the Call-Info header field value defined in
   [I-D.ietf-sipcore-callinfo-rcd] with a type of "jcard".  As also
   defined in [I-D.ietf-sipcore-callinfo-rcd], format of the jCard and
   properties used should follow the normative usage and formatting
   rules and procedures.  It is an extensible object where the calling
   party can provide both the standard types of information defined in
   jCard or can use the built-in extensibility of the jCard
   specification to add additional information.  The "jcd" key is
   optional.  If included, this key MUST only be included once in the
   "rcd" JSON object and MUST NOT be included if there is a "jcl" key
   included.  The use of "jcd" and "jcl" keys are mutually exclusive.

   The jCard object value for "jcd" MUST only have referenced content
   for URI values that do not further reference URIs.  Future
   specifications may extend this capability, but as stated in
   [I-D.ietf-sipcore-callinfo-rcd] it constrains the security properties
   of RCD information and the integrity of the content referenced by
   URIs.

   Note: even though we refer to [I-D.ietf-sipcore-callinfo-rcd] as the
   definition of the jcard properties for usage in an "rcd" PASSporT,
   other future specifications and protocols are encouraged to be
   adapted for use of "jcd" (or similarly "jcl" below) key beyond SIP
   and Call-Info.

5.1.5.  "jcl" key

   The "jcl" key value is defined to contain a URI that refers the
   recipient to a jCard [RFC7095] JSON object hosted on a HTTPS enabled
   web server.  The web server MUST use the MIME media type for JSON
   text as application/json with a default encoding of UTF-8 [RFC4627].
   This link may derive from the Call-Info header field value defined in
   [I-D.ietf-sipcore-callinfo-rcd] with a type of "jcard".  As also
   defined in [I-D.ietf-sipcore-callinfo-rcd], format of the jCard and
   properties used should follow the normative usage and formatting
   rules and procedures.  The "jcl" key is optional.  If included, this
   key MUST only be included once in the "rcd" JSON object and MUST NOT
   be included if there is a "jcd" key included.  The use of "jcd" and
   "jcl" keys are mutually exclusive.

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   The jCard object referenced by the URI value for "jcl" MUST only have
   referenced content for URI values that do not further reference URIs.
   Future specifications may extend this capability, but as stated in
   [I-D.ietf-sipcore-callinfo-rcd] it constrains the security properties
   of RCD information and the integrity of the content referenced by
   URIs.

6.  "rcdi" RCD Integrity Claim Definition and Usage

   The "rcdi" claim is included for the second and fourth modes
   described in the integrity overview Section 4 of this document.  If
   this claim is present it MUST be included only once with the
   corresponding single "rcd" claim.  The value of the "rcdi" claim is a
   JSON object that is defined as follows.

   The claim value of "rcdi" claim key is a JSON object with a set of
   JSON key/value pairs.  These objects correspond to each of the
   elements of the "rcd" claim object that require integrity protection
   with an associated digest over the content referenced by the key
   string.  The individual digest of different elements of the "rcd"
   claim data and external URI referenced content is kept specifically
   separate to allow the ability to verify the integrity of only the
   elements that are ultimately retrieved or downloaded or rendered to
   the end-user.

   The key value references a specific object within the "rcd" claim
   value using a JSON pointer defined in [RFC6901] with a minor
   additional rule to support external URI references that include JSON
   objects themselves, for the specific case of the use of "jcl".  JSON
   pointer syntax is the key value that specifies exactly the part of
   JSON that is used to generate the digest which produce the resulting
   string that makes up the value for the corresponding key.  Detailed
   procedures are provided below, but an example "rcdi" is provided
   here:

   "rcdi" : {
     "/jcl": "sha256-7kdCBZqH0nqMSPsmABvsKlHPhZEStgjojhdSJGRr3rk",
     "/jcl/1/2/3": "sha256-jL4f47fF82LuwcrOrSyckA4SWrlElfARHkW6kYo1JdI"
   }

   The values of each key/value pair consists of a digest across either
   the direct values or indirectly referenced resources, combined with a
   string that defines the crypto algorithm used to generate the digest.
   RCD implementations MUST support the following hash algorithms,
   "SHA256", "SHA384", and "SHA512".  The SHA-256, SHA-384, and SHA-512
   are part of the SHA-2 set of cryptographic hash functions defined by
   the National Institute of Standards and Technologies (NIST).
   Implementations MAY support additional algorithms, but MUST NOT

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   support known weak algorithms such as MD5 or SHA-1.  In the future,
   the list of algorithms may be re-evaluated based on security best
   practices.  The algorithms are represented in the text by "sha256",
   "sha384", or "sha512".  The character following the algorithm string
   MUST be a minus character, "-".  The subsequent characters are the
   base64 encoded [RFC4648] digest of a canonicalized and concatenated
   string or binary data based on the JSON pointer referenced elements
   of "rcd" claim or the URI referenced content contained in the claim.
   The details of the determination of the input string used to
   determine the digest are defined in the next section.

6.1.  Creation of the "rcd" element digests

   "rcd" claim objects can contain "nam", "apn", "icn", "jcd", or "jcl"
   keys as part of the "rcd" JSON object claim value.  This
   specification defines the use of JSON pointer [RFC6901] as a
   mechanism to reference specific "rcd" claim elements.

   In order to facilitate proper verification of the digests and whether
   the "rcd" elements or content referenced by URIs were modified, the
   input to the digest must be completely deterministic at three points
   in the process.  First, at the certification point where the content
   is evaluated to conform to the application policy and the JWT Claim
   Constraints is applied to the certificate containing the digest.
   Second, when the call is signed at the Authentication Service, there
   may be a local policy to verify that the provided "rcd" claim
   corresponds to each digest.  Third, when the "rcd" data is verified
   at the Verification Service, the verification is performed for each
   digest by constructing the input digest string for the element being
   verified and referenced by the JSON pointer string.

   The procedure for the creation of each "rcd" element digest string
   corresponding to a JSON pointer string key is as follows.

   1.  The JSON pointer either refers to a value that is a part or the
       whole of a JSON object or to a string that is a URI referencing
       an external resource.

   2.  For a JSON value, serialize the JSON to remove all white space
       and line breaks.  The procedures of this deterministic JSON
       serialization are defined in [RFC8225], Section 9.  The resulting
       string is the input for the hash function.

   3.  For any URI referenced content, the bytes of the body of the HTTP
       response is the input for the hash function.

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6.1.1.  "nam" and "apn" elements

   In the case of "nam" and "apn", the only allowed value is a string.
   For both of these key values an "rcdi" JSON pointer or integrity
   digest is optional because the direct value is protected by the
   signature and can be constrained directly with JWTClaimConstraints.
   If used, the JSON key value referenced by the JSON pointer is the
   string includes the quotes, so quotes MUST be included to compute the
   digest.

6.1.2.  "icn" elements

   In the case of "icn", the only allowed value is a URI value that
   references an image file.  If the URI references externally linked
   content there would need to be a JSON pointer and digest entry for
   the content in that linked resource.  In order to reference the "icn"
   value for a digest, the JSON pointer string would be "/icn" and the
   digest string would be created using the image file data following
   the rules of JSON pointer.  Even though this is probably not the
   typical case, an "rcdi" JSON pointer or integrity digest is optional
   if the image value is directly included via a data URI.  However,
   even though the direct value can be protected by the signature and
   can be constrained directly with JWTClaimConstraints, since the
   length of the image data is likely much larger than the integrity
   digest, this specification would recommend the use of the "rcdi" JSON
   pointer and integrity digest as the constraint value in
   JWTClaimConstraints over the image data.

6.1.3.  "jcd" elements

   In the case of "jcd", the value associated is a jCard JSON object,
   which happens to be a JSON array with sub-arrays.  JSON pointer
   notation uses numeric indexes into elements of arrays, including when
   those elements are arrays themselves.

   As example, for the following "rcd" claim:

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   "rcd": {
     "jcd": ["vcard",
       [ ["version",{},"text","4.0"],
         [“fn",{},"text","Q Branch"],
         [“org",{},"text","MI6;Q Branch Spy Gadgets"],
         ["photo",{},"uri",
           "https://example.com/photos/quartermaster-256x256.png"],
         ["logo",{},"uri",
           "https://example.com/logos/mi6-256x256.jpg"],
         ["logo",{},"uri",
           "https://example.com/logos/mi6-64x64.jpg"]
       ]
     ],
     "nam": "Q Branch Spy Gadgets"
   }

   In order to use JSON pointer to refer to the URIs, the following
   example "rcdi" claim includes a digest for the entire "jcd" array
   string as well as three additional digests for the URIs, where, as
   defined in [RFC6901] zero-based array indexes are used to reference
   the URI strings.

   "rcdi": {
     "/jcd": "sha256-tbxXX9mRY2dtss3vNdNkNkt9hrV9N1LqGST2hDlw97I",
     "/jcd/1/3/3": "sha256-RojgWwU6xUtI4q82+kHPyHm1JKbm7+663bMvzymhkl4",
     "/jcd/1/4/3": "sha256-jL4f47fF82LuwcrOrSyckA4SWrlElfARHkW6kYo1JdI",
     "/jcd/1/5/3": "sha256-GKNxxqlLRarbyBNh7hc/4lbZAdK6B0kMRf1AMRWPkSo"
     }
   }

   The use of a JSON pointer and integrity digest for the "jcd" claim
   key and value is optional.  The "jcd" value is the directly included
   jCard array and can be protected by the signature and can be
   constrained directly with JWTClaimConstraints.  However, for data
   length reasons (as with "icn" above) or more importantly for
   potential privacy and/or security considerations with a publically
   accessible certificate this specification would recommend the use of
   the "rcdi" JSON pointer and integrity digest as the contraint value
   in JWTClaimConstraints over the jCard data.

   It is important to remember the array indexes for JSON Pointer are
   dependent on the order of the elements in the jCard.  The use of
   digest for the "/jcd" corresponding to the entire jCard array string
   can be included as a redundant mechanism to avoid any possibility of
   substitution, insertion attacks, or other potential techniques that
   may be possible to avoid integrity detection.

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   Each URI referenced in the jCard array string MUST have a
   corresponding JSON pointer string key and digest value.

6.1.4.  "jcl" elements

   In the case of the use of a "jcl" URI reference to an external jCard,
   the procedures are similar to "jcd" with the exception and the minor
   modification to JSON pointer, where "/jcl" is used to refer to the
   external jCard array string and any following numeric array indexes
   added to the "jcl" (e.g., "/jcl/1/2/3") are treated as if the
   externally referenced jCard was directly part of the overall "rcd"
   claim JSON object.  The following example illustrates a "jcl" version
   of the above "jcd" example.

   "rcd": {
     "jcl": "https://example.com/qbranch.json",
     "nam": "Q Branch Spy Gadgets"
   },
   "rcdi": {
     "/jcl": "sha256-Gb0lOkj7Z9+plqbOkN32H+YX0Yav3fbioSk7DxQdGZU",
     "/jcl/1/3/3": "sha256-RojgWwU6xUtI4q82+kHPyHm1JKbm7+663bMvzymhkl4",
     "/jcl/1/4/3": "sha256-jL4f47fF82LuwcrOrSyckA4SWrlElfARHkW6kYo1JdI",
     "/jcl/1/5/3": "sha256-GKNxxqlLRarbyBNh7hc/4lbZAdK6B0kMRf1AMRWPkSo"
   }

   The following is the example contents of resource pointed to by
   https://example.com/qbranch.json used to calculate the above digest
   for "/jcl"

   ["vcard",
     [ ["version",{},"text","4.0"],
       [“fn",{},"text","Q Branch"],
       [“org",{},"text","MI6;Q Branch Spy Gadgets"]
       ["photo",{},"uri",
         "https://example.com/photos/quartermaster-256x256.png"]
       ["logo",{},"uri",
         "https://example.com/logos/mi6-256x256.jpg"]
       ["logo",{},"uri",
         "https://example.com/logos/mi6-64x64.jpg"]
     ]
   ]

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6.2.  JWT Claim Constraints for "rcd" claims only

   For the third mode described in the integrity overview Section 4 of
   this document, where only JWT Claim Constraints for "rcd" claims
   without an "rcdi" claim is required, the procedure when creating the
   certificate with the intent to always include an "rcd" claim, to
   include a JWT Claim Constraints on inclusion of an "rcd" claim with
   the intended values required to be constrained by the certificate
   used to sign the PASSporT.

   The "permittedValues" for the "rcd" claim may optionally contain
   multiple entries, to support the case where the certificate holder is
   authorized to use different sets of rich call data.

   Only including "permittedValues" for "rcd" (with no "mustInclude")
   provides the ability to either have no "rcd" claim or only the set of
   constrained "permittedValues" values for an included "rcd" claim.

7.  JWT Claim Constraints usage for "rcd" and "rcdi" claims

   The integrity overview Section 4 of this document describes a fourth
   mode where both "rcdi" and JWT Claim Constraints is used.  The use of
   this mode implies the signing of an "rcdi" claim is required to be
   protected by the authoritative certificate creator using JWT Claims
   Constraints in the certificate.  The objective of the use of both of
   these mechanisms is to constrain the signer to construct the "rcd"
   and "rcdi" claims with the "rcd" jCard object including reference
   external content via URI.  Once both the contents of the "rcd" claim
   and any linked content is certified by the party that is
   authoritative for the certificate being created and the construction
   of the "rcdi" claim is complete, the "rcdi" claim is linked to the
   STIR certificate associated with the signature in the PASSporT via
   JWT Claim Constraints extension as defined in [RFC8226] Section 8.
   It should be recognized that the "rcdi" set of digests is intended to
   be unique for only a specific combination of "rcd" content and URI
   referenced external content, and therefore provides a robust
   integrity mechanism for an authentication service being performed by
   a non-authoritative party.  This would often be associated with the
   use of delegate certificates [RFC9060] for the signing of calls by
   the calling party directly as an example, even though the "authorized
   party" is not necessarily the subject of a STIR certificate.

   For the case that there should always be both "rcd" and "rcdi" values
   included in the "rcd" PASSporT, the certificate JWT Claims Constraint
   extension MUST include both of the following:

   *  a "mustInclude" for the "rcd" claim, which simply constrains the
      fact that an "rcd" must be included

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   *  a "mustInclude" for the "rcdi" claim and a "permittedValues" equal
      to the created "rcdi" claim value string.

   Note that optionally the "rcd" claims may be included in the
   "permittedValues" however it is recognized that this may be redundant
   with the "rcdi" permittedValues because the "rcdi" digest will imply
   the content of the "rcd" claims themselves.

   The "permittedValues" for the "rcdi" claims (or "rcd" claims more
   generally) may contain multiple entries, to support the case where
   the certificate holder is authorized to use different sets of rich
   call data.

8.  PASSporT "crn" claim - Call Reason Definition and Usage

   This specification defines a new JSON Web Token claim for "crn", Call
   Reason, the value of which is a single string or object that can
   contains information as defined in [I-D.ietf-sipcore-callinfo-rcd]
   corresponding to the "call-reason" parameter for the Call-Info
   header.  This claim is optional.

   Example "crn" claim with "rcd":

   "crn" : "For your ears only",
   "rcd": { "nam": "James Bond",
            "jcl": "https://example.org/james_bond.json"}

   As also noted in [I-D.ietf-sipcore-callinfo-rcd] this claim is
   included as corresponding to "call-reason" Call-Info parameter, but
   there is an alternative suggested way to include call-reason which is
   to use the "cif" claim with a "call-reason" key value, as defined
   below in this document.

8.1.  JWT Constraint for "crn" claim

   The integrity of the "crn" claim can optionally be protected by the
   authoritative certificate creator using JWT Constraints in the
   certificate.  If the intent of the issuer of the certificate is to
   always including a call reason, a "mustInclude" for the "crn" claim
   indicates that a "crn" claim must be present.  If the issuer of the
   certificate wants to constrain the contents of "crn", then it may set
   "permittedValues" for "crn" in the certificate.

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9.  Rich Call Data Claims Usage Rules

   Either or both the "rcd" or "crn" claims may appear in any PASSporT
   claims object as optional elements.  The creator of a PASSporT MAY
   also add a "ppt" value of "rcd" to the header of a PASSporT as well,
   in which case the PASSporT claims MUST contain either an "rcd" or
   "crn" claim, and any entities verifying the PASSporT object are
   required to understand the "ppt" extension in order to process the
   PASSporT in question.  An example PASSporT header with the "ppt"
   included is shown as follows:

   { "typ":"passport",
     "ppt":"rcd",
     "alg":"ES256",
     "x5u":"https://www.example.com/cert.cer" }

   The PASSporT claims object contains 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].

   After the header and claims PASSporT objects have been constructed,
   their signature is generated normally per the guidance in [RFC8225].

9.1.  "rcd" PASSporT Verification

   An "rcd" PASSporT that uses claims defined in this specification, in
   order to have a successful verification outcome, MUST conform to the
   following:

   *  have a valid signature

   *  abide by all rules set forth in the proper construction of the
      claims

   *  abide by JWT Claims Constraint rules defined in [RFC8226]
      Section 8 or extended in [RFC9118] if present in the certificate
      used to sign the PASSporT

   Consistent with the verification rules of PASSporTs more generally
   [RFC8225], if any of the above criteria is not met, relying parties
   MUST NOT use any of the claims in the PASSporT.

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9.2.  "rcdi" Integrity Verification

   If the "rcdi" claim exists, any party that dereferences a URI (i.e.
   downloading content for display to users) from the "rcd" claim MUST
   perform integrity validation of the content against the corresponding
   digest.  Consequently, if URIs with contents covered by integrity
   digests are passed to another entity, the corresponding integrity
   digest MUST also be included, for example by passing the PASSporT.
   Entities that pass on the content without the URI do not have to pass
   on the corresponding integrity digest.  An entity that does not
   otherwise need to dereference a URI from the "rcd" claim would be
   discouraged from unnecessarily dereferencing the URI solely to
   perform integrity verification.

   If there is any issue with completing the integrity verification
   procedures for externally referenced content, including HTTP or HTTPS
   errors, the referenced content MUST be considered not verified.  This
   SHOULD NOT however impact the result of base PASSporT verification
   for claims content that is directly included in the claims of the
   PASSporT.

9.3.  Example "rcd" PASSporTs

   An example of a "nam" only PASSporT claims object is shown next (with
   line breaks for readability only).

   {  "orig":{"tn":"12025551000"},
      "dest":{"tn":["12025551001"]},
      "iat":1443208345,
      "rcd":{"nam":"James Bond"} }

   An example of a "nam" and "apn" only PASSporT claims object is shown
   next (with line breaks for readability only).

   {  "orig":{"tn":"12025551000"},
      "dest":{"tn":["12155551001"]},
      "iat":1443208345,
      "rcd":{
        "apn":"12025559990",
        "nam":"Her Majesty's Secret Service" } }

   An example of an "rcd" claims object that includes the "jcd" and also
   contains URI references to content which requires the inclusion of an
   "rcdi" claim and corresponding digests.

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 {
   "crn": "Rendezvous for Little Nellie",
   "orig": { "tn": "12025551000"},
   "dest": { "tn": ["12155551001"]},
   "iat": 1443208345,
   "rcd": {
     "jcd": ["vcard",
     [ ["version",{},"text","4.0"],
       ["fn",{},"text","Q Branch"],
       ["org",{},"text","MI6;Q Branch Spy Gadgets"],
       ["photo",{},"uri","https://example.com/photos/q-256x256.png"],
       ["logo",{},"uri","https://example.com/logos/mi6-256x256.jpg"],
       ["logo",{},"uri","https://example.com/logos/mi6-64x64.jpg"]
     ] ],
     "nam": "Q Branch Spy Gadgets"
   },
   "rcdi": {
     "/jcd/1/3/3": "sha256-RojgWwU6xUtI4q82+kHPyHm1JKbm7+663bMvzymhkl4",
     "/jcd/1/4/3": "sha256-jL4f47fF82LuwcrOrSyckA4SWrlElfARHkW6kYo1JdI",
     "/jcd/1/5/3": "sha256-GKNxxqlLRarbyBNh7hc/4lbZAdK6B0kMRf1AMRWPkSo"
   }
 }

   In an example PASSporT, where a jCard is linked via HTTPS URL using
   "jcl", a jCard file served at a particular URL.

   An example jCard JSON file hosted at the example web address of
   https://example.com/qbranch.json is shown as follows:

   ["vcard",
     [ ["version",{},"text","4.0"],
       ["fn",{},"text","Q Branch"],
       ["org",{},"text","MI6;Q Branch Spy Gadgets"],
       ["photo",{},"uri","https://example.com/photos/q-256x256.png"],
       ["logo",{},"uri","https://example.com/logos/mi6-256x256.jpg"],
       ["logo",{},"uri","https://example.com/logos/mi6-64x64.jpg"]
     ]
   ]

   For the above referenced jCard, the corresponding PASSporT claims
   object would be as follows:

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 {
   "crn": "Rendezvous for Little Nellie",
   "orig": {"tn": "12025551000"},
   "dest": {"tn": ["12155551001"]},
   "iat": 1443208345,
   "rcd": {
     "nam": "Q Branch Spy Gadgets",
     "jcl": "https://example.com/qbranch.json"
   },
   "rcdi": {
     "/jcl": "sha256-qCn4pEH6BJu7zXndLFuAP6DwlTv5fRmJ1AFkqftwnCs",
     "/jcl/1/3/3": "sha256-RojgWwU6xUtI4q82+kHPyHm1JKbm7+663bMvzymhkl4",
     "/jcl/1/4/3": "sha256-jL4f47fF82LuwcrOrSyckA4SWrlElfARHkW6kYo1JdI",
     "/jcl/1/5/3": "sha256-GKNxxqlLRarbyBNh7hc/4lbZAdK6B0kMRf1AMRWPkSo"
   }
 }

   An example "rcd" PASSporT that uses "nam" and "icn" keys with "rcdi"
   for calling name and referenced icon image content:

   {
     "crn": "Rendezvous for Little Nellie",
     "orig": {"tn": "12025551000"},
     "dest": {"tn": ["12155551001"]},
     "iat": 1443208345,
     "rcd": {
       "nam": "Q Branch Spy Gadgets",
       "icn": "https://example.com/photos/q-256x256.png"
     },
     "rcdi": {
       "/nam": "sha256-sM275lTgzCte+LHOKHtU4SxG8shlOo6OS4ot8IJQImY",
       "/icn": "sha256-RojgWwU6xUtI4q82+kHPyHm1JKbm7+663bMvzymhkl4"
     }
   }

10.  Compact form of "rcd" PASSporT

10.1.  Compact form of the "rcd" PASSporT claim

   Compact form of an "rcd" PASSporT claim has some restrictions that
   will be enumerated below, but mainly follows standard PASSporT
   compact form procedures.  For re-construction of the "nam" claim the
   string for the display-name in the From header field. "jcl" and "jcd"
   MAY NOT be used with compact form due to integrity rules and URI
   reference rules in this specification leading to too restrictive of a
   set of constraints.  Future specifications may revisit this to
   propose a consisent and comprehensive way of addressing integrity and
   security of information.

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10.2.  Compact form of the "rcdi" PASSporT claim

   Compact form of an "rcdi" PASSporT claim is not supported, so if
   "rcdi" is required compact form MUST NOT be used.

10.3.  Compact form of the "crn" PASSporT claim

   Compact form of a "crn" PASSporT claim shall be re-constructed using
   the "call-reason" parameter of a Call-Info header as defined by
   [I-D.ietf-sipcore-callinfo-rcd].

11.  Further Information Associated with Callers

   Beyond naming information and the information that can be contained
   in a jCard [RFC7095] object, 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 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 17.3.  Specific extensions to the "rcd" PASSporT claim are
   left for future specification.

   There is a few ways RCD can be extended in the future, jCard is an
   extensible object and the key/values in the RCD claim object can also
   be extended.  General guidance for future extensibility that were
   followed by the authors is that jCard generally should refer to data

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   that references the caller as an individual or entity, where other
   claims, such as "crn" refer to data regarding the specific call.
   There may be other considerations discovered in the future, but this
   logical grouping of data to the extent possible should be followed
   for future extensibility.

12.  Third-Party Uses

   While rich data about the call can be provided by an originating
   authentication service, an intermediary in the call path could also
   acquire rich call data by querying a third-party service.  Such a
   service effectively acts as a STIR Authentication Service, generating
   its own PASSporT, and that PASSporT could be attached to a SIP call
   by either the originating or terminating side.  This third-party
   PASSporT attests information about the calling number, rather than
   the call or caller itself, and as such its RCD MUST NOT be used when
   a call lacks a first-party PASSporT that assures verification
   services that the calling party number is not spoofed.  It is
   intended to be used in cases when the originating side does not
   supply a display-name for the caller, so instead some entity in the
   call path invokes a third-party service to provide rich caller data
   for a call.

   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 third party's signature over the
   data, and the potential for the PASSporT to be conveyed from
   intermediaries to endpoint devices.  Effectively, these use cases
   form a sub-case of out-of-band [RFC8816] 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 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.

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

   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.  When those elements are present, they MUST be in
   a third-party "rcd" PASSporT using "iss" claim described in the next
   section.

12.1.  Signing as a Third Party

   A third-party PASSporT contains an "iss" element to distinguish its
   PASSporTs from first-party PASSporTs.  Third-party "rcd" PASSporTs
   are signed with credentials that do not have authority over the
   identity that appears in the "orig" element of the PASSporT claims.
   The presence of "iss" signifies that a different category of
   credential is being used to sign a PASSporT than the [RFC8226]
   certificates used to sign STIR calls; it is instead a certificate
   that identifies the source of the "rcd" data.  How those credentials
   are issued and managed is outside the scope of this specification;
   the value of "iss" however MUST reflect the Subject of the
   certificate used to sign a third-party PASSporT.  The explicit
   mechanism for reflecting the subject field of the certificate is out
   of scope of this document and left to the certificate governance
   policies that define how to map the "iss" value in the PASSporT to
   the subject field in the certificate.  Relying parties in STIR have
   always been left to make their own authorization decisions about
   whether to 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.

   An example of a Third Party issued PASSporT claims object is as
   follows.

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   {  "orig":{"tn":"12025551000"},
      "dest":{"tn":["12025551001"]},
      "iat":1443208345,
      "iss":"Zorin Industries",
      "rcd":{"nam":"James St. John Smythe"} }

13.  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, third-party PASSporTs that
   carry "rcd" data MUST also carry an indication of the relationship of
   the generator of the PASSporT to the caller in the form of the "iss"
   claim.  As stated in the previous section, the use of "iss" MUST
   reflect the subject field of the certificate used to sign a third-
   party PASSporT to represent that relationship.

14.  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"
   claim.

14.1.  Authentication Service Behavior

   An authentication service creating a PASSporT containing an "rcd"
   claim MAY include a "ppt" for "rcd" or not.  Third-party
   authentication services following the behavior in Section 12.1 MUST
   include a "ppt" of "rcd".  If "ppt" does contain an "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:

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   Identity: sv5CTo05KqpSmtHt3dcEiO/1CWTSZtnG3iV+1nmurLXV/HmtyNS7Ltrg9
          dlxkWzoeU7d7OV8HweTTDobV3itTmgPwCFjaEmMyEI3d7SyN21yNDo2ER/Ovgt
          w0Lu5csIppPqOg1uXndzHbG7mR6Rl9BnUhHufVRbp51Mn3w0gfUs=;
          info=<https://biloxi.example.org/biloxi.cer>;alg=ES256;
          ppt="rcd"

   This specification assumes that by default, a SIP authentication
   service derives the value of "rcd", specifically only for the "nam"
   key value, from the display-name component of the From header field
   value of the request, alternatively for some calls this may come from
   the P-Asserted-ID header.  It is however a matter of authentication
   service policy to decide how it populates the value of "nam" key,
   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 an "rcd" claim containing "nam" 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.

14.2.  Verification Service Behavior

   [RFC8224] 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 "nam" key when it recomputes the
   header and claims of the PASSporT object.  Additionally, if there
   exists a Call-Info header field as defined in
   [I-D.ietf-sipcore-callinfo-rcd], the "jcard" value can be derived to
   determine the "jcd" 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 allows SIP networks that convey the display name through a field
   other than the From header field to interoperate with this
   specification.  Similarly, the "jcd" or linked "jcl" jcard
   information and "crn" can be optionally, based on local policy for
   devices that support it, used to populate a Call-Info header field
   following the format of [I-D.ietf-sipcore-callinfo-rcd].

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   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 12.1.  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 an "rcd" claim largely remains 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.

15.  Using "rcd" and "rcdi" as additional claims to other PASSporT
     extensions

   Rich Call Data, including calling name information, as a common
   example, is often data that is additive to the personal
   communications information defined in the core PASSporT data required
   to support the security properties defined in [RFC8225].  For cases
   where the entity originating the personal communications is
   supporting the authentication service for the calling identity and is
   the authority of the Rich Call Data, rather than creating multiple
   Identity header fields cooresponding to multiple PASSporT extensions,
   the authentication service can alternatively directly add the "rcd"
   claim to a PASSporT that authenticates the calling identity.

   Note: There is one very important caveat to this capability, because
   generally if there is URI referenced content in an "rcd" PASSporT
   there is often the requirement to use "rcdi" and JWT Claims

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   Constraints.  So, it is important for the user of this specification
   to recognize that the certificates used should include the necessary
   JWT Claims Constraints for proper integrity and security of the
   values in the "rcd" claim incorporated into PASSporTs that are not
   "rcd".

15.1.  Procedures for applying "rcd" as claims only

   For a given PASSporT using some other extension than "rcd", the
   Authentication Service MAY additionally include the "rcd" claim as
   defined in this document.  This would result in a set of claims that
   correspond to the original intended extension with the addition of
   the "rcd" claim.

   The Verification service that receives the PASSporT, if it supports
   this specification and chooses to, should interpret the "rcd" claim
   as simply just an additional claim intended to deliver and/or
   validate delivered Rich Call Data.

15.2.  Example for applying "rcd" as claims only

   In the case of [RFC8588] which is the PASSporT extension supporting
   the SHAKEN specification [ATIS-1000074.v002], a common case for an
   Authentication service to co-exist in a CSP network along with the
   authority over the calling name used for the call.  Rather than
   require two identity headers, the CSP Authentication Service can
   apply both the SHAKEN PASSporT claims and extension and simply add
   the "rcd" required claims defined in this document.

   For example, the PASSporT claims for the "shaken" PASSporT with "rcd"
   claims would be as follows:

   Protected Header
   {
      "alg":"ES256",
      "typ":"passport",
      “ppt”:”shaken”,
      "x5u":"https://cert.example.org/passport.cer"
   }
   Payload
   {
      “attest”:”A”,
      "dest":{“tn”:["12025551001"]},
      "iat":1443208345,
      "orig":{“tn”:"12025551000"},
      “origid”:”123e4567-e89b-12d3-a456-426655440000”,
      "rcd":{"nam":"James Bond"}
   }

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   A Verification Service that supports "rcd" and "shaken" PASSporT
   extensions is able to receive the above PASSporT and interpret both
   the "shaken" claims as well as the "rcd" defined claim.

   If the Verification Service only understands the "shaken" PASSporT
   extension claims and doesn't support "rcd" PASSporT extension, then
   the "rcd" claim is used during PASSporT signature validation but is
   otherwise ignored and disregarded.

16.  Acknowledgements

   We would like to thank David Hancock, Robert Sparks, Russ Housley,
   Eric Burger, Alec Fenichel, Ben Campbell, Jack Rickard, Jordan
   Simpson for helpful suggestions, review, and comments.

17.  IANA Considerations

17.1.  JSON Web Token Claim

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

   Claim Name: "rcd"

   Claim Description: Rich Call Data Information

   Change Controller: IESG

   Specification Document(s): [RFCThis]

   Claim Name: "rcdi"

   Claim Description: Rich Call Data Integrity Information

   Change Controller: IESG

   Specification Document(s): [RFCThis]

   Claim Name: "crn"

   Claim Description: Call Reason

   Change Controller: IESG

   Specification Document(s): [RFCThis]

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17.2.  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
   [RFCThis].

17.3.  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 four values, "nam",
   "apn", "jcd", and "jcl", which are specified in [RFCThis].

18.  Security Considerations

   Whether its identities, alternate identities, images, logos, physical
   addresses, all of the information contained in a RCD PASSporT must
   follow some form of vetting in which the authoritative entity or user
   of the information being signed MUST follow an applicable policy of
   the eco-system using RCD.  This can be of many forms, depending on
   the setup and constraints of the eco-system so is therefore out-of-
   scope of this document.  However, the general chain of trust that
   signers of RCD PASSporT are either directly authoritative or have
   been delegated authority through certificates using JWT Claim
   Constraints and integrity mechanisms defined in this and related
   documents is critical to maintain the integrity of the eco-system
   utilizing this and other STIR related specifications.

   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
   SIP.

   The use of JWTClaimConstraints, a mechanism defined in [RFC8226] and
   extended in [RFC9118] to constrain any of the RCD information in the
   public certificate by including that information in the certificate,
   depending on the availbility in the deployment of the PKI system, may
   present a privacy issue.  The use of "rcdi" claim and digests for
   representing JWT claim contents may be a recommended way of
   preventing the exposure of that information through the certificates
   which are often publically accessible and available.

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   Since computation of "rcdi" digests for URIs requires the loading of
   referenced content, it would be best practice to validate that
   content at the creation of the "rcdi" or corresponding JWT claim
   constraint value by checking for content that may cause issues for
   verification services or that doesn't follow the behavior defined in
   this document, e.g., unreasonably sized data, the inclusion of
   recursive URI references, etc.  Along the same lines, the
   verification service should also use precautionary best practices to
   avoid attacks when accessing URI linked content.

18.1.  The use of JWT Claim Constraints in delegate certificates to
       exclude unauthorized claims

   While this can apply to any PASSporT that is signed with a STIR
   Delegate Certificates [RFC9060], it is important to note that when
   constraining PASSporTs to include specific claims or contents of
   claims, it is also important to consider potential attacks by non-
   authorized signers that may include other potential PASSporT claims
   that weren't originally vetted by the authorized entity providing the
   delegate certificate.  The use of JWT claims constraints as defined
   in [RFC9118] for preventing the ability to include claims beyond the
   claims defined in this document may need to be considered.

   Certificate issuers SHOULD NOT include an entry in mustExclude for
   the "rcdi" claim for a certificate that will be used with the
   PASSporT Extension for Rich Call Data defined in this document.
   Excluding this claim would prevent the integrity protection mechanism
   from working properly.

19.  References

19.1.  Normative References

   [I-D.ietf-sipcore-callinfo-rcd]
              Wendt, C. and J. Peterson, "SIP Call-Info Parameters for
              Rich Call Data", Work in Progress, Internet-Draft, draft-
              ietf-sipcore-callinfo-rcd-04, 7 March 2022,
              <https://www.ietf.org/archive/id/draft-ietf-sipcore-
              callinfo-rcd-04.txt>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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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,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              DOI 10.17487/RFC3325, November 2002,
              <https://www.rfc-editor.org/info/rfc3325>.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627,
              DOI 10.17487/RFC4627, July 2006,
              <https://www.rfc-editor.org/info/rfc4627>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/info/rfc6901>.

   [RFC7095]  Kewisch, P., "jCard: The JSON Format for vCard", RFC 7095,
              DOI 10.17487/RFC7095, January 2014,
              <https://www.rfc-editor.org/info/rfc7095>.

   [RFC7340]  Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
              Telephone Identity Problem Statement and Requirements",
              RFC 7340, DOI 10.17487/RFC7340, September 2014,
              <https://www.rfc-editor.org/info/rfc7340>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8224]  Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 8224,
              DOI 10.17487/RFC8224, February 2018,
              <https://www.rfc-editor.org/info/rfc8224>.

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   [RFC8225]  Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
              Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
              <https://www.rfc-editor.org/info/rfc8225>.

   [RFC8226]  Peterson, J. and S. Turner, "Secure Telephone Identity
              Credentials: Certificates", RFC 8226,
              DOI 10.17487/RFC8226, February 2018,
              <https://www.rfc-editor.org/info/rfc8226>.

   [RFC8588]  Wendt, C. and M. Barnes, "Personal Assertion Token
              (PaSSporT) Extension for Signature-based Handling of
              Asserted information using toKENs (SHAKEN)", RFC 8588,
              DOI 10.17487/RFC8588, May 2019,
              <https://www.rfc-editor.org/info/rfc8588>.

   [RFC9060]  Peterson, J., "Secure Telephone Identity Revisited (STIR)
              Certificate Delegation", RFC 9060, DOI 10.17487/RFC9060,
              September 2021, <https://www.rfc-editor.org/info/rfc9060>.

   [RFC9118]  Housley, R., "Enhanced JSON Web Token (JWT) Claim
              Constraints for Secure Telephone Identity Revisited (STIR)
              Certificates", RFC 9118, DOI 10.17487/RFC9118, August
              2021, <https://www.rfc-editor.org/info/rfc9118>.

19.2.  Informative References

   [ATIS-1000074.v002]
              ATIS/SIP Forum NNI Task Group, "Signature-based Handling
              of Asserted information using toKENs (SHAKEN)
              <https://access.atis.org/apps/group_public/
              download.php/62391/ATIS-1000074.v002.pdf>", November 2021.

   [RFC8816]  Rescorla, E. and J. Peterson, "Secure Telephone Identity
              Revisited (STIR) Out-of-Band Architecture and Use Cases",
              RFC 8816, DOI 10.17487/RFC8816, February 2021,
              <https://www.rfc-editor.org/info/rfc8816>.

Authors' Addresses

   Chris Wendt
   Somos Inc.
   Email: chris-ietf@chriswendt.net

   Jon Peterson
   Neustar Inc.
   Email: jon.peterson@neustar.biz

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