



Internet Engineering Task Force (IETF)                          C. Wendt
Request for Comments: 9795                                    Somos Inc.
Category: Standards Track                                    J. Peterson
ISSN: 2070-1721                                               TransUnion
                                                               July 2025


    Personal Assertion Token (PASSporT) Extension for Rich Call Data

Abstract

   This document extends Personal Assertion Token (PASSporT), a token
   for conveying cryptographically signed call information about
   personal communications, to include rich metadata 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.  It is also enhanced with
   an integrity mechanism that is designed to protect the authoring and
   transport of this information for different authoritative use cases.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9795.

Copyright Notice

   Copyright (c) 2025 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 extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Overview of the Use of the Rich Call Data PASSporT Extension
   4.  Overview of Rich Call Data Integrity
   5.  "rcd" PASSporT Claim: Definition and Usage
     5.1.  PASSporT "rcd" Claim
       5.1.1.  "nam" key
       5.1.2.  "apn" key
       5.1.3.  "icn" key
       5.1.4.  "jcd" key
       5.1.5.  "jcl" key
   6.  "rcdi" PASSporT Claim: Definition and Usage
     6.1.  Creation of the "rcd" Element Digests
       6.1.1.  "nam" and "apn" Elements
       6.1.2.  "icn" Elements
       6.1.3.  "jcd" Elements
       6.1.4.  "jcl" Elements
     6.2.  JWT Claim Constraints for "rcd" Claims
     6.3.  JWT Claim Constraints for "rcd" and "rcdi" Claims
   7.  "crn" PASSporT Claim: Definition and Usage
     7.1.  JWT Constraint for "crn" Claim
   8.  Rich Call Data Claims Usage Rules
     8.1.  "rcd" PASSporT Verification
     8.2.  "rcdi" Integrity Verification
     8.3.  Example "rcd" PASSporTs
   9.  Compact Form of "rcd" PASSporT
     9.1.  Compact Form of the "rcd" PASSporT Claim
     9.2.  Compact Form of the "rcdi" PASSporT Claim
     9.3.  Compact Form of the "crn" PASSporT Claim
   10. Third-Party Uses
     10.1.  Signing as a Third Party
     10.2.  Verification Using Third-Party RCD
   11. Levels of Assurance
   12. Use of "rcd" PASSporTs in SIP
     12.1.  Authentication Service Behavior for SIP Protocol
     12.2.  Verification Service Behavior for SIP Protocol
   13. Using "rcd", "rcdi", and "crn" as Additional Claims to Other
           PASSporT Extensions
     13.1.  Procedures for Applying RCD Claims as Claims Only
     13.2.  Example for Applying RCD Claims as Claims Only
   14. Further Information Associated with Callers
   15. IANA Considerations
     15.1.  JSON Web Token Claim
     15.2.  Personal Assertion Token (PASSporT) Extensions
     15.3.  PASSporT RCD Claim Types
   16. Security Considerations
     16.1.  Use of JWT Claim Constraints in Delegate Certificates to
            Exclude Unauthorized Claims
   17. References
     17.1.  Normative References
     17.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   PASSporT [RFC8225] is a token format based on JSON Web Token (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
   Secure Telephone Identity Revisited (STIR) problem statement
   [RFC7340] declared securing the display name of callers outside of
   STIR's initial scope.  This document extends the use of JWT and
   PASSporT in the overall STIR framework by defining a PASSporT
   extension and the associated STIR procedures to protect additional
   caller- and call-related information.  This is information beyond the
   calling party originating identity (e.g., telephone number or SIP
   URI) that is intended to be rendered to assist a called party in
   determining whether to accept or trust incoming communications.  This
   includes information such as the name of the person or entity on one
   side of a communications session, for example, 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 to a call and whom is calling.

   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 determine a name from
   the calling party number by consulting a local address book or an
   external database.  SIP, for example, similarly can carry this
   information in a display-name in the From header field value (or
   alternatively the Call-Info header field) from the originating to
   terminating side.  In this document, we utilize the STIR framework to
   more generally extend the assertion of an extensible set of identity
   information not limited to but including calling name.

   This document extends PASSporT to provide cryptographic protection
   for the "display-name" field of SIP requests, or similar name fields
   in other protocols, 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.  In
   addition, Section 12 describes use cases that enable external third-
   party authorities to convey rich information associated with a
   calling number via an "rcd" PASSporT while clearly identifying the
   third-party as the source of the Rich Call Data information.
   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, therefore limiting a PASSporT and the RCD
   claims it asserts via certificate-level controls.

2.  Terminology

   The key words "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

   This document defines Rich Call Data (RCD), which is a PASSporT
   extension [RFC8225] that defines an extensible claim for asserting
   information about the call beyond the telephone number.  This
   includes more detailed information about the calling party, calling
   number, or the purpose of the call.  There are many use cases that
   this document describes around the entities responsible for the
   signing and integrity of this information, whether it is the entity
   that originates a call, a service provider acting on behalf of a
   caller, or when third-party services may be authoritative over the
   RCD on behalf of the caller.  In general, PASSporT [RFC8225] has been
   defined to be independent of the communications protocol, but its
   initial usage as detailed in [RFC8224] is with the SIP protocol
   [RFC3261].  There are many SIP-specific references and definitions in
   this document, but future specifications may extend the usage of RCD
   PASSporTs and claims to other protocol-specific usage and
   definitions.

   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 information about a caller associated with
   "display-name" in SIP [RFC3261], typically a textual description of
   the caller, or alternate presentation numbers often used in the From
   header field [RFC3261] or P-Asserted-Identity header field [RFC3325],
   or an icon associated with the caller.  The second category is a set
   of RCD that is defined as part of the jCard definitions or extensions
   to that data.  [RFC9796] describes the optional use of jCard in the
   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 as defined in this document.

   Additionally, in relation to the description of the specific
   communications event itself (versus the identity description in the
   previous paragraph), [RFC9796] 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 a string 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 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 are policy and
   restrictions around what data elements are allowed to be used.
   Whether preventing offensive language or icons, enforcing uniqueness,
   notifying about potential trademark or copyright violations, or
   enforcing other policies, there might be the desire to pre-certify or
   "vet" the specific use of RCD.  This document defines a mechanism
   that allows for a direct or indirect party that (a) enforces the
   policies to approve or certify the content, (b) creates a
   cryptographic digest that can be used to validate that data, and (c)
   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 its 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 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 [W3C-SubresourceIntegrity].  The second of the
   mechanisms uses the capability called JWT Claim Constraints, defined
   in [RFC8226] and extended in [RFC9118].  The JWT Claim Constraints
   specifically guide the verifier within the certificate used to
   compute the signature in 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 RCD
   conveyed in the PASSporT claims is passed 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 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 ecosystem the "rcd" PASSporTs or
   "rcd" claims 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 URI refs         | Includes URI refs                |
   +==========+=====================+==================================+
   | Auth     | 1: No integrity req | 2: RCD Integrity                 |
   +==========+---------------------+----------------------------------+
   | Non-Auth | 3: JWT Claim Const. | 4: RCD Integ. /                  |
   |          |                     | JWT Claim Const.                 |
   +==========+---------------------+----------------------------------+

                                  Table 1

   The first and simplest mode is exclusively for when all RCD content
   is directly included as part of the claims (i.e., no URIs referencing
   external content 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.

   The third and fourth modes 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, in
   particular when delegating signing authority for PASSporT, for agreed
   or vetted content to be 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 referenced external content using URIs.

5.  "rcd" PASSporT Claim: Definition and Usage

5.1.  PASSporT "rcd" Claim

   This document 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, match the
   display-name component of the From header field value of a SIP
   request [RFC3261] or alternatively of the P-Asserted-Identity header
   field value [RFC3325], or a similar field in other PASSporT using
   protocols.  This key MUST be included once as part of the "rcd" claim
   value JSON object.  The key syntax of "nam" MUST follow the display-
   name ABNF given in [RFC3261].  If there is no string associated with
   a display name, the claim value MUST 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, match 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 of the Additional-
   Identity header field value [TS.3GPP.24.229], 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.

   The use of the optional "apn" key is intended for cases where the
   signer of an "rcd" PASSporT or "rcd" claims 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 or "rcd" claims.  The use of the "apn"
   key 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 HTTPS URL reference to an image
   resource 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 is used to
   protect the Call-Info header field with a purpose parameter value of
   "icon" as described in Section 20.9 of [RFC3261].  For example:

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

   Note that [RFC9796] 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 for "jcd" and
   "jcl" key values (Sections 5.1.4 and 5.1.5) and in [RFC9796], there
   are alternative ways of including photos and logos as HTTPS URL
   references.  The "icn" key should be 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 what
   each image type represents for the proper rendering to end users.

5.1.4.  "jcd" key

   The "jcd" key value is defined to contain a jCard JSON object
   [RFC7095].  The jCard is defined in this specification as an
   extensible object format used to contain RCD information about the
   call initiator.  This object is intended to directly match the Call-
   Info header field value defined in [RFC9796] with a type of "jcard",
   where the format of the jCard and properties used should follow the
   normative usage and formatting rules and procedures in that document.
   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.  Either a "jcd" or "jcl" MAY
   appear in the "rcd" claim, but not both.

   The jCard object value for "jcd" MUST be a jCard JSON object that MAY
   have URI-referenced content, but that URI-referenced content MUST NOT
   further reference URIs.  Future specifications may extend this
   capability, but [RFC9796] constrains the security properties of RCD
   information and the integrity of the content referenced by URIs.

      |  Note: Even though we refer to [RFC9796] as the definition of
      |  the jCard properties for usage in "rcd" claims, using the Call-
      |  Info header field with RCD information in a SIP request beyond
      |  the use of identity header as defined in this document is not
      |  required.  Identity header fields are generally encouraged for
      |  all transport of authenticated and protected RCD information
      |  over Network-to-Network Interfaces (NNIs) between untrusted
      |  parties or over untrusted networks.  The use of Call-Info
      |  header fields to carry RCD information as defined in [RFC9796]
      |  is suggested for use in trusted networks relationships,
      |  generally for User-Network Interfaces (UNIs).

5.1.5.  "jcl" key

   The "jcl" key value is an HTTPS URL that refers to a jCard JSON
   object [RFC7095] on a web server.  The web server MUST use the media
   type for JSON text as application/json with a default encoding of
   UTF-8 [RFC8259].  This link may correspond to the Call-Info header
   field value defined in [RFC9796] with a type of "jcard".  As also
   defined in [RFC9796], the format of the jCard and properties used
   should follow the normative usage and formatting rules and
   procedures.  The "jcl" key is optional.  The "jcd" or "jcl" keys MAY
   only appear once in the "rcd" claim but MUST be mutually exclusive.

   The jCard object referenced by the URI value for "jcl" MUST be a
   jCard JSON object that MAY have URI-referenced content, but that URI-
   referenced content MUST NOT further reference URIs.  Future
   specifications may extend this capability, but [RFC9796] constrains
   the security properties of RCD information and the integrity of the
   content referenced by URIs.

6.  "rcdi" PASSporT Claim: Definition and Usage

   The "rcdi" claim is included for the second and fourth modes
   described in the integrity overview (Section 4). "rcdi" and "rcd"
   claims MAY each appear once in a PASSporT, but if "rcdi" is included,
   the "rcd" MUST be present correspondingly.  The value of the "rcdi"
   claim is a JSON object that is defined as follows.

   The claim value of the "rcdi" claim key is a JSON object with a set
   of JSON key/value pairs.  Each "rcdi" claim key/value pair
   corresponds 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 URI-referenced
   external content is kept specifically separate to allow the ability
   to verify the integrity of only the elements that are ultimately
   retrieved, 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 URI references to external content that
   include JSON objects themselves, for the specific case of the use of
   "jcl", defined in Section 6.1.4.  JSON pointer syntax is the key
   value that documents exactly the part of JSON that is used to
   generate the digest that produces 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 one of
   the following objects referenced by the JSON pointer key:

   *  the content inline to the referenced object,

   *  the content of a resource referenced by an inline URI object, or

   *  the content of a resource specified by a URI that is in embedded
      in content specified by an inline URI object (e.g., "jcl")

   This is combined with a string that defines the cryptographic
   algorithm used to generate the digest.  RCD implementations MUST
   support the hash algorithms SHA-256, SHA-384, and SHA-512.  These
   hash algorithms are identified by "sha256", "sha384", and "sha512",
   respectively.  SHA-256, SHA-384, and SHA-512 are part of the SHA-2
   set of cryptographic hash functions [RFC6234] defined by the US
   National Institute of Standards and Technology (NIST).
   Implementations MAY support additional recommended hash algorithms in
   [IANA-COSE-ALG], that is, the hash algorithms with "Yes" in the
   "Recommended" column of the IANA registry.  Hash algorithm
   identifiers MUST use only lowercase letters, and they MUST NOT
   contain hyphen characters.  The character following the algorithm
   string MUST be a hyphen character ("-", %x2D).  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 the "rcd" claim or the URI-referenced content
   contained in the claim.  The next section covers the details of the
   determination of the input string used to determine the digest.

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 document
   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 to
   determine 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, it must be
   deterministic at the certification point when the content is
   evaluated to conform to the application policy and when the JWT Claim
   Constraints are 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 are the input for the hash function.

   Note that the digest is computed on the JSON representation of the
   string, which necessarily includes the beginning and ending double-
   quote characters.

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 JWT Claim Constraints.

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 MUST be a JSON pointer and digest entry for the
   content in that linked resource.  When creating a key/value
   representing "icn", the key is the JSON pointer string "/icn", and
   the digest value string is created using the image file byte data
   referenced in the URI.

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 indices into elements of arrays, including when
   those elements are arrays themselves.

   As an example, we have the following "rcd" claim:

   "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 a 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 indices are used to reference
   the URI strings.

   "rcdi": {
     "/jcd": "sha256-7kdCBZqH0nqMSPsmABvsKlHPhZEStgjojhdSJGRr3rk",
     "/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; it can be protected by the signature and can be
   constrained directly with JWT Claim Constraints.  However, for data
   length reasons (as with "icn" above) or more importantly for
   potential privacy and/or security considerations with a publicly
   accessible certificate, the use of the "rcdi" JSON pointer and
   integrity digest as the constraint value in JWT Claim Constraints
   over the jCard data is RECOMMENDED.

   It is important to remember the array indices 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 to
   undermine integrity detection.

   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 minor modification to
   the JSON pointer, where "/jcl" is used to refer to the external jCard
   array string.  Also, any following numeric array indices added to the
   "jcl" (e.g., "/jcl/1/2/3") are treated as if the external content
   referenced by the jCard were 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": "sha256-7kdCBZqH0nqMSPsmABvsKlHPhZEStgjojhdSJGRr3rk",
     "/jcl/1/3/3": "sha256-RojgWwU6xUtI4q82+kHPyHm1JKbm7+663bMvzymhkl4",
     "/jcl/1/4/3": "sha256-jL4f47fF82LuwcrOrSyckA4SWrlElfARHkW6kYo1JdI",
     "/jcl/1/5/3": "sha256-GKNxxqlLRarbyBNh7hc/4lbZAdK6B0kMRf1AMRWPkSo"
   }

   The "rcdi" MUST have a "/jcl" key value and digest value to protect
   the referenced jCard object, and each URI referenced in the
   referenced jCard array string MUST have a corresponding JSON pointer
   string key and digest value.

   The following is the example contents of the resource pointed to by
   https://example.com/qbranch.json; it is 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"]
     ]
   ]

6.2.  JWT Claim Constraints for "rcd" Claims

   When using JWT Claim Constraints for "rcd" claims, the procedure when
   creating the signing certificate should adhere to the following
   guidelines.

   The "permittedValues" for the "rcd" claim MAY contain a single entry
   or optionally MAY contain multiple entries with the intent of
   supporting cases where the certificate holder is authorized to use
   different sets of rich call data corresponding to different call
   scenarios.

   Only including "permittedValues" for "rcd", with no "mustInclude",
   provides the ability for the construction a valid PASSporT that can
   either have no "rcd" claim within or only the set of constrained
   "permittedValues" values for an included "rcd" claim.

6.3.  JWT Claim Constraints for "rcd" and "rcdi" Claims

   The use of JWT Claim Constraints with an "rcdi" claim is for cases
   where URI-referenced content is to be protected by the authoritative
   certificate issuer.  The objective for the use of JWT Claim
   Constraints for the combination of both "rcd" and "rcdi" claims is to
   constrain the signer to only construct the "rcd" and "rcdi" claims
   inside a PASSporT to contain and reference only a predetermined set
   of content.  Once both the contents of the "rcd" claim and any
   referenced content are certified by the party that is authoritative
   for the certificate being issued to the signer, the "rcdi" claim is
   constructed and linked to the STIR certificate associated with the
   signature in the PASSporT via the JWT Claim Constraints extension as
   defined in [RFC8226], Section 8 and extended in [RFC9118].  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 the set provides a robust integrity
   mechanism for an authentication service being performed by a non-
   authoritative party.  For example, this may be used with delegate
   certificates [RFC9060] for the signing of calls by the calling party
   directly, even though the "authorized party" is not necessarily the
   subject of a STIR certificate.

   For the cases where both "rcd" and "rcdi" claims should always be
   included in the 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

   *  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 RCD.

7.  "crn" PASSporT Claim: Definition and Usage

   This document defines a new JSON Web Token claim for "crn", Call
   Reason, the value of which is a single string that can contain
   information as defined in [RFC9796] and 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"}

7.1.  JWT Constraint for "crn" Claim

   The integrity of the "crn" claim contents can optionally be protected
   by the authoritative certificate issuer using JWT Claim Constraints
   in the certificate.  When the signer of the PASSporT intends to
   always include a call reason string of any value, a "mustInclude" for
   the "crn" claim in the JWT Claim Constraints indicates that a "crn"
   claim must always be present and is RECOMMENDED to be included by the
   certificate issuer.  If the signer of the "crn" claim wants to
   constrain the contents of "crn", then "permittedValues" for "crn" in
   JWT Claim Constraints should match the contents of the allowed
   strings and is RECOMMENDED to be included by the certificate issuer.

8.  Rich Call Data Claims Usage Rules

   The "rcd" or "crn" claims MAY appear in any PASSporT claims object as
   optional elements.  The creator of a PASSporT MAY also add a PASSporT
   extension ("ppt") value, defined in [RFC8225], Section 8.1, of "rcd"
   to the header of a PASSporT.  In that case, the PASSporT claims MUST
   contain at least one "rcd" or "crn" claim (or both).  Any entities
   verifying the PASSporT claims defined in this document are required
   to understand the PASSporT extension in order to process the PASSporT
   in question.  An example PASSporT header with the PASSporT extension
   ("ppt") value of "rcd" 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" key and value, is mandatory.

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

8.1.  "rcd" PASSporT Verification

   A verifier that successfully verifies a PASSporT that contains an
   "rcd" claim MUST ensure the following about the PASSporT:

   *  It has a valid signature per the verification procedures detailed
      in [RFC8225].

   *  It abides by all rules set forth in the proper construction of the
      claims defined in Section 5.

   *  It abides by JWT Claims Constraint rules defined in [RFC8226],
      Section 8 or extended by [RFC9118] if present in the certificate
      used to compute the signature in the PASSporT.

   In addition, if the "iss" claim is included in the PASSporT,
   verification should follow procedures described in Section 10.2.

   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.

8.2.  "rcdi" Integrity Verification

   When the "rcdi" claim exists, the verifier should verify the digest
   for each JSON pointer key.  Any digest string that doesn't match a
   generated digest MUST be considered a failure of the verification of
   the content referenced by the JSON pointer.

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

   As a potential optimization of verification procedures, an entity
   that does not otherwise need to dereference a URI from the "rcd"
   claim for display to the end user is NOT RECOMMENDED to unnecessarily
   dereference the URI solely to perform integrity verification.

8.3.  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", "apn", and "icn" using an https URI PASSporT
   claims object is shown next (with line breaks for readability only).
   Note, in this example, there is no integrity protection over the
   "icn" element in the "rcd" claim.

   {  "orig":{"tn":"12025551000"},
      "dest":{"tn":["12155551001"]},
      "iat":1443208345,
      "rcd":{
        "apn":"12025559990",
        "icn":"https://example.com/photos/quartermaster-256x256.png",
        "nam":"Her Majesty's Secret Service" } }

   An example of a "nam", "apn", and "icn" using data URI PASSporT
   claims object is shown next (with line breaks for readability only).
   Note, in this example, the "icn" data is incorporated directly in the
   "rcd" claim, and therefore separate integrity protection is not
   required.

   {  "orig":{"tn":"12025551000"},
      "dest":{"tn":["12155551001"]},
      "iat":1443208345,
      "rcd":{
        "apn":"12025559990",
        "icn":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAY
          AAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OH
          wAAAABJRU5ErkJggg==",
        "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 require the inclusion of an
   "rcdi" claim and corresponding digests.  Note, in this example, the
   "rcdi" claim includes integrity protection of the URI-referenced
   content.

   {
     "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 the following PASSporT example, a jCard is linked via HTTPS URL
   using "jcl", and a jCard file is served at a particular URL.

   Example jCard JSON file hosted at https://example.com/qbranch.json:

   ["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:

   {
     "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"
     }
   }

9.  Compact Form of "rcd" PASSporT

9.1.  Compact Form of the "rcd" PASSporT Claim

   The specific usage of the compact form of an "rcd" PASSporT claim,
   defined in [RFC8225], Section 7, has some restrictions that will be
   enumerated below, but it mainly follows standard PASSporT compact
   form procedures.  Compact form only provides the signature from the
   PASSporT, requiring the reconstruction of the other PASSporT claims
   from the SIP header fields as discussed in Section 4.1 of [RFC8224].

   The reconstruction of the "nam" claim, if using the SIP protocol,
   should use the display-name string in the From header field.  For
   other protocols, if there is a display name field that exists, the
   string should be used; otherwise, the string should be an empty
   string, e.g., "".  The claims "jcl" and "jcd" MUST NOT be used with
   compact form because the integrity rules and URI reference rules
   defined in this document would lead a set of constraints that is too
   restrictive.  Future specifications may revisit this to propose a
   consistent and comprehensive way of addressing integrity and security
   of information and to provide specific guidance for other protocol
   usage.

9.2.  Compact Form of the "rcdi" PASSporT Claim

   The use of the compact form of a PASSporT using an "rcdi" claim is
   not supported, so if "rcdi" is required, compact form MUST NOT be
   used.

9.3.  Compact Form of the "crn" PASSporT Claim

   Compact form of a "crn" PASSporT claim shall be reconstructed using
   the "call-reason" parameter of a Call-Info header as defined by
   [RFC9796].

10.  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 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.  A third-party
   PASSporT 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 use cases [RFC8816].  The manner in
   which third-party services are discovered is outside the scope of
   this document.

   An intermediary use case might look as follows using the SIP protocol
   for this example: 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 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
   PASSporT object matches, or is string-equivalent to, 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
   "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 the "iss" claim described in the
   next section.

10.1.  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 certificates (as
   defined in [RFC8226]) 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
   document; however, the value of "iss" 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; 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 PASSporT claims object issued by a third party is as
   follows.

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

10.2.  Verification Using Third-Party RCD

   The third-party "rcd" PASSporT cases must be considered in the
   verification service, 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.
   Following the rules of [RFC8225] and in particular if there are
   multiple identity headers (as in the case of the inclusion of an
   "rcd" and "shaken" PASSporTs from two different signing providers), 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.  It is possible that
   if multiple identity headers are present, only the verified identity
   information should be considered when presenting call information to
   an end user.

   Verification services may alter their authorization policies for the
   credentials accepted to sign PASSporTs when third parties generate
   PASSporT objects, per Section 10.1.  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.

11.  Levels of Assurance

   A set of "rcd" claims can be provided by either first-party providers
   that are directly authorized to sign PASSporTs in the STIR ecosystem
   or third-party providers that are indirectly or delegated authority
   to sign PASSporTs.  Relying parties could benefit from an additional
   claim that indicates the identification, in the form of a uniquely
   identifiable name, of the attesting party to the caller.  Even in
   first-party cases, 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 be determined 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 are RECOMMENDED to also carry an indication of the
   identity of the generator of the PASSporT in the form of the 'iss'
   claim.

12.  Use of "rcd" PASSporTs in SIP

   This section documents SIP-specific usage for "rcd" PASSporTs in the
   SIP Identity header field value.  Other protocols using PASSporT may
   define their own guidance for "rcd" PASSporTs.

12.1.  Authentication Service Behavior for SIP Protocol

   An authentication service creating a PASSporT containing an "rcd"
   claim MAY include a PASSporT extension ("ppt" value) of "rcd".
   Third-party authentication services following the behavior in
   Section 10.1 MUST include a PASSporT extension value of "rcd".  If
   the PASSporT extension does contain an "rcd", then any SIP
   authentication services MUST add a PASSporT extension "ppt" parameter
   to the Identity header field containing that PASSporT with a value of
   "rcd".  The resulting Identity header field might look as follows:

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

   This document assumes that by default when using the SIP protocol, an
   authentication service determines 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 the "nam" key, which MAY also match or be determined by
   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 string-
   equivalent to the From header field display-name value, it MUST use
   the full form of the PASSporT object in SIP.

   In addition, [RFC9796] defines a Call-Info header field that MAY be
   used as a source of RCD information that an authentication service
   uses to construct the appropriate PASSporT RCD claim types used.

   Note also that, as a best practice, the accuracy and legitimacy of
   Rich Call Data information that is included in the claims is
   RECOMMENDED to follow a trust framework that is out of scope of this
   document.  As with telephone numbers for the STIR framework, the
   authentication of Rich Call Data should follow some type of vetting
   process by an entity that is authoritative over determining the
   accuracy and legitimacy of that information.  This includes the
   mechanisms for how and from whom that information is received by the
   authentication service.  For example, the general use of Call-Info
   via SIP as a trusted source of RCD information on the authentication
   side is NOT RECOMMENDED.

12.2.  Verification Service Behavior for SIP Protocol

   [RFC8224], Section 6.2, Step 5 requires that future specifications
   defining PASSporT extension ("ppt") values describe any additional
   verifier behavior specific to the SIP protocol.  The general
   verification procedures defined in Section 8.1 should be followed,
   but the following paragraphs describe some of the specifics needed to
   implement a verification service using the SIP protocol.

   If the PASSporT is in compact form, then the verification service
   MUST extract the display-name from the From header field value, if
   any, and MUST use that as the string 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
   [RFC9796], the "jcard" JSON object value MUST be used to construct
   the "jcd" key value when it recomputes the header and claims of the
   PASSporT object.  If the signature validates over the recomputed
   object, then the verification is considered successful.

   If the PASSporT is in full form with a PASSporT extension value of
   "rcd", then the verification service MUST extract the value
   associated with the "rcd" claim "nam" key in the object.  If the
   PASSporT signature is verified successfully, then the verification
   service MUST additionally compare the string value of the "rcd" claim
   "nam" key value with the From header field value or the preferred
   value.  The preferred value depends on local policy of the SIP
   network technique that conveys the display name string through a
   field other than the From header field to interoperate with this
   specification (e.g., P-Asserted-Identity) as discussed in [RFC8224].
   Similarly, "jcd", "jcl", "icn", "apn", or "crn" elements can be used
   optionally (based on local policy for devices that support it) to
   populate a Call-Info header field following the format of [RFC9796].
   If PASSporT RCD claims types defined in the future are present, they
   should follow similar defined procedures and policies.

   The behavior of a SIP User Agent Server (UAS) upon receiving an
   INVITE or other type of session initiation request 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.

13.  Using "rcd", "rcdi", and "crn" 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 corresponding to multiple PASSporT extensions,
   the authentication service can alternatively directly add the "rcd"
   claim to a PASSporT that authenticates the calling identity.

13.1.  Procedures for Applying RCD Claims as Claims Only

   For a given PASSporT using some other extension than "rcd", the
   Authentication Service MAY additionally include the "rcd" defined in
   Section 5, "rcdi" defined in Section 6, and "crn" defined in
   Section 7 claims.  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.

13.2.  Example for Applying RCD Claims as Claims Only

   In the case of [RFC8588], which is the PASSporT extension supporting
   the Signature-based Handling of Asserted information using toKENs
   (SHAKEN) specification [ATIS-1000074.v003], a common case is for an
   authentication service to coexist 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"}
   }

   A verification service that understands and supports claims defined
   in the "rcd" and "shaken" PASSporT extensions is able to receive the
   above PASSporT and interpret both the "shaken" claims as well as the
   "rcd" claims.

   If the verification service only understands the "shaken" PASSporT
   extension claims and doesn't support the "rcd" PASSporT extension or
   claims, then the "rcd" claim in this example is used during PASSporT
   signature validation but is otherwise ignored and disregarded.

14.  Further Information Associated with Callers

   Beyond naming information and the information that can be contained
   in a jCard object [RFC7095], 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; it 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 (whether this a
      government agency, 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 15.3.  Specific extensions to the "rcd" PASSporT claim are
   left for future specification.

   There are 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 was
   followed by the authors is that jCard typically should refer to data
   that references the caller as an individual or entity, whereas 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 should be followed to the extent possible
   for future extensibility.

15.  IANA Considerations

15.1.  JSON Web Token Claim

   Per this document, IANA has added 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:  IETF
   Reference:  RFC 9795

   Claim Name:  "rcdi"
   Claim Description:  Rich Call Data Integrity Information
   Change Controller:  IETF
   Reference:  RFC 9795

   Claim Name:  "crn"
   Claim Description:  Call Reason
   Change Controller:  IETF
   Reference:  RFC 9795

15.2.  Personal Assertion Token (PASSporT) Extensions

   Per this document, IANA has added a new entry to the "Personal
   Assertion Token (PASSporT) Extensions" registry for the type "rcd"
   which is specified in this document.

15.3.  PASSporT RCD Claim Types

   IANA has created a new "PASSporT RCD Claim Types" registry in the
   "Personal Assertion Token (PASSporT)" registry group.  Registration
   of new PASSporT RCD claim types shall be under the Specification
   Required policy [RFC8126].

   This registry is initially populated with five claim name values,
   "nam", "apn", "icn", "jcd", and "jcl", which are specified in this
   document.  The columns are "Name" and "Reference".  Any new
   registrations should consist of only of the name and the reference
   document.  There is an obligation for expert review, where the
   designated expert should validate that the proposed new PASSporT RCD
   claim type has a scope that doesn't potentially conflict or overlap
   with the usage or interpretation of the other existing types in the
   registry.

16.  Security Considerations

   The process of signing information contained in a "rcd" PASSporT
   (whether the identities, identifiers, alternate identities or
   identifiers, images, logos, physical addresses, or otherwise) should
   follow some vetting process in which an authoritative entity follows
   an appropriate consistent policy defined and governed by the
   ecosystem using RCD and the STIR framework.  This can be of many
   forms, depending on the setup and constraints of the policy
   requirements of the ecosystem, and 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 ecosystem 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 in many current base communications protocols
   (for example, SIP) is information that is carried 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 dereferencing and download of any RCD URI-linked resources as
   part of verification either in-network or on device could provide
   some level of information about calling patterns, so this should be
   considered when making these resources available.

   The use of JWT Claim Constraints, 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 availability in the deployment of the
   PKI system, may present a privacy issue.  The use of the "rcdi" claim
   and digests for representing JWT claim contents is RECOMMENDED for
   the prevention of the exposure of that information through the
   certificates that are often publicly accessible and available.

   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.

   As general guidance, the use of URLs and URIs that reference
   potentially dangerous or intentionally harmful content should be
   considered in implementing this specification.  [RFC3986], Section 7
   contains good additional guidance to consider when communicating or
   dereferencing URLs and URIs.

16.1.  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 Certificate [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.

17.  References

17.1.  Normative References

   [IANA-COSE-ALG]
              IANA, "COSE Algorithms",
              <https://www.iana.org/assignments/cose>.

   [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>.

   [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>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [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>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,
              <https://www.rfc-editor.org/info/rfc6234>.

   [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>.

   [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>.

   [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>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [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>.

   [RFC9796]  Wendt, C. and J. Peterson, "SIP Call-Info Parameters for
              Rich Call Data", RFC 9796, DOI 10.17487/RFC9796, July
              2025, <https://www.rfc-editor.org/info/rfc9796>.

17.2.  Informative References

   [ATIS-1000074.v003]
              Alliance for Telecommunications Industry Solutions,
              "Signature-based Handling of Asserted information using
              toKENs (SHAKEN)", ATIS-1000074.v003, August 2022,
              <https://access.atis.org/higherlogic/ws/public/
              download/67436>.

   [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>.

   [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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [TS.3GPP.24.229]
              3GPP, "IP multimedia call control protocol based on
              Session Initiation Protocol (SIP) and Session Description
              Protocol (SDP); Stage 3", 16.7.0, 3GPP TS 24.229,
              September 2020,
              <https://www.3gpp.org/ftp/Specs/html-info/24229.htm>.

   [W3C-SubresourceIntegrity]
              Braun, F., Ed., "Subresource Integrity", W3C First Public
              Working Draft, 25 April 2025,
              <https://www.w3.org/TR/2025/WD-sri-2-20250422/>.

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.

Authors' Addresses

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


   Jon Peterson
   TransUnion
   Email: jon.peterson@transunion.com
