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PASSporT Extension for Rich Call Data
draft-ietf-stir-passport-rcd-26

Document Type Active Internet-Draft (stir WG)
Authors Chris Wendt , Jon Peterson
Last updated 2023-07-24 (Latest revision 2023-06-05)
Replaces draft-peterson-stir-cnam
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Nov 2019
Submit PASSPorT Extension for rich call data for publication as Proposed Standard
Document shepherd Russ Housley
Shepherd write-up Show Last changed 2022-09-20
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Details
draft-ietf-stir-passport-rcd-26
Network Working Group                                           C. Wendt
Internet-Draft                                                Somos Inc.
Intended status: Standards Track                             J. Peterson
Expires: 7 December 2023                                    Neustar Inc.
                                                             5 June 2023

                 PASSporT Extension for Rich Call Data
                    draft-ietf-stir-passport-rcd-26

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 and is also enhanced with a
   integrity mechanism that is designed to protect the authoring and
   transport of this information for different authoritative use-cases.

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 7 December 2023.

Copyright Notice

   Copyright (c) 2023 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.

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   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  . . . . . . . . .  15
     6.3.  JWT Claim Constraints usage for "rcd" and "rcdi"
           claims  . . . . . . . . . . . . . . . . . . . . . . . . .  15
   7.  PASSporT "crn" claim - Call Reason Definition and Usage . . .  16
     7.1.  JWT Constraint for "crn" claim  . . . . . . . . . . . . .  16
   8.  Rich Call Data Claims Usage Rules . . . . . . . . . . . . . .  16
     8.1.  "rcd" PASSporT Verification . . . . . . . . . . . . . . .  17
     8.2.  "rcdi" Integrity Verification . . . . . . . . . . . . . .  17
     8.3.  Example "rcd" PASSporTs . . . . . . . . . . . . . . . . .  18
   9.  Compact form of "rcd" PASSporT  . . . . . . . . . . . . . . .  21
     9.1.  Compact form of the "rcd" PASSporT claim  . . . . . . . .  21
     9.2.  Compact form of the "rcdi" PASSporT claim . . . . . . . .  21
     9.3.  Compact form of the "crn" PASSporT claim  . . . . . . . .  21
   10. Third-Party Uses  . . . . . . . . . . . . . . . . . . . . . .  21
     10.1.  Signing as a Third Party . . . . . . . . . . . . . . . .  23
     10.2.  Verification using Third Party RCD . . . . . . . . . . .  23
   11. Levels of Assurance . . . . . . . . . . . . . . . . . . . . .  24
   12. Use of "rcd" PASSporTs in SIP . . . . . . . . . . . . . . . .  24
     12.1.  Authentication Service Behavior for SIP protocol . . . .  25
     12.2.  Verification Service Behavior for SIP protocol . . . . .  26
   13. Using "rcd", "rcdi", "crn" as additional claims to other
           PASSporT extensions . . . . . . . . . . . . . . . . . . .  27

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     13.1.  Procedures for applying RCD claims as claims only  . . .  27
     13.2.  Example for applying RCD claims as claims only . . . . .  27
   14. Further Information Associated with Callers . . . . . . . . .  28
   15. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  29
   16. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
     16.1.  JSON Web Token Claim . . . . . . . . . . . . . . . . . .  29
     16.2.  Personal Assertion Token (PASSporT) Extensions . . . . .  30
     16.3.  PASSporT RCD Claim Types . . . . . . . . . . . . . . . .  30
   17. Security Considerations . . . . . . . . . . . . . . . . . . .  30
     17.1.  The use of JWT Claim Constraints in delegate certificates
            to exclude unauthorized claims . . . . . . . . . . . . .  32
   18. References  . . . . . . . . . . . . . . . . . . . . . . . . .  32
     18.1.  Normative References . . . . . . . . . . . . . . . . . .  32
     18.2.  Informative References . . . . . . . . . . . . . . . . .  34
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  34

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.  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 additional
   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.

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   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 from
   the originating to terminating side, or alternatively in the Call-
   Info header field.  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 a "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 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

   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 information such as more detailed information about the
   calling party or calling number being presented or the purpose of the
   call.  There are many use-cases that will be described in this
   document 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
   use-cases where third-party services may be authoritative over the
   rich call data on behalf of the caller.  In general, PASSporT
   [RFC8225] has been defined to be a communications protocol
   independent technology, but it's initial usage as detailed in

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   [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 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-Identity [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.
   [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 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, 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 are policy and
   restrictions around what data elements are 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 enforces
   the policies 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

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   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 rich
   call data conveyed in the PASSporT claims is pass-by-value or pass-
   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 eco-system 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. |
   +----------+---------------------+--------------------------------+

   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

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   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, to enable
   a mechanism for allowing agreed 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 referenced external
   content using URIs.

5.  PASSporT Claim "rcd" 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 from 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 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 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 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

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   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.  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 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 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 HTTPS URL 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.  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 [I-D.ietf-sipcore-callinfo-rcd] 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 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 "rcd" claims, using
   Call-Info as protocol with the addition of an identity header
   carrying the PASSPorT is not required.  The identity header carrying
   a PASSporT with "rcd" claim including a "jcd" value can be used as
   the primary and only transport of the RCD information.

5.1.5.  "jcl" key

   The "jcl" key value is an HTTPS URL that refers to a jCard [RFC7095]
   JSON object on a web server.  The web server MUST use the MIME 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 [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.  The
   "jcd" or "jcl" keys MAY only appear once in the "rcd" claim but MUST
   be mutually exclusive.

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   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 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.
   "rcdi" and "rcd" claims MAY each appear once in a PASSporT, but if
   "rcdi" is included the "rcd" MUST correspondingly be present also.
   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 URI referenced external 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 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 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 one of
   the following objects referenced by the JSON pointer key,

   *  content inline to the referenced object

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

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   *  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 crypto 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 algorithm has "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, "-", or
   ASCII 45.  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 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 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.

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   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.

   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 JWTClaimConstraints.

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 would be 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 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 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 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, the use of the "rcdi" JSON pointer and
   integrity digest as the constraint value in JWTClaimConstraints 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 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 indices
   added to the "jcl" (e.g., "/jcl/1/2/3") are treated as if the
   external content referenced by the 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": "sha256-7kdCBZqH0nqMSPsmABvsKlHPhZEStgjojhdSJGRr3rk",
     "/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 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

   When using JWT Claim Constraints for "rcd" claims the procedure when
   creating the signing certificate should follow 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 usage 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 pre-determined set
   of content.  Once both the contents of the "rcd" claim and any
   referenced content is 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 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 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 cases that there should always be both "rcd" and "rcdi"
   claims 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

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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.

7.  PASSporT "crn" claim - Call Reason 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 [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"}

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 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 as well, in which case the PASSporT
   claims MUST contain at least one or both an "rcd" or "crn" claim.
   Any entities verifying the PASSporT claims defined in this document

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   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 PASSportT 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 of this document

   *  it abides by JWT Claims Constraint rules defined in [RFC8226]
      Section 8 or extended in [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.

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   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.  This
   SHOULD NOT however 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 procedure, an entity that
   does not otherwise need to dereference a URI from the "rcd" claim for
   display to 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.

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   {  "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 requires 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 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:

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   ["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"
     }
   }

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9.  Compact form of "rcd" PASSporT

9.1.  Compact form of the "rcd" PASSporT claim

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

   The re-construction of the "nam" claim, if using 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.,
   "". "jcl" and "jcd" MUST NOT be used with compact form due to
   integrity rules and URI reference rules in this document leading to
   too restrictive of a set of constraints.  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 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 re-constructed using
   the "call-reason" parameter of a Call-Info header as defined by
   [I-D.ietf-sipcore-callinfo-rcd].

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.  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

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   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 using 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 equivelent 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.

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   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.

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 [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 document; 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.

   {  "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 is

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   multiple identity headers, for example with 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 there is 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

   As "rcd" can be provided by either first party providers that are
   directly authorized to sign PASSporTs in the STIR eco-system 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 and in
   the SIP Identity header field value.  Other using protocols of
   PASSporT may define their own usages for the "rcd" PASSporTs.

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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" or not.
   Third-party authentication services following the behavior in
   Section 10.1 MUST include a PASSporT extension value of "rcd".  If
   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 "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, {I-D.ietf-sipcore-callinfo-rcd}} defines a Call-Info
   header field that MAY be used as a source of RCD information that an
   authentication services 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.

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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 proceedures 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
   [I-D.ietf-sipcore-callinfo-rcd], 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" or "jcl" jcard information, "icn", "apn", or "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].  If future defined PASSporT RCD
   claims types are present, they should follow similar defined
   proceedures and policies.

   The behavior of a SIP 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.

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13.  Using "rcd", "rcdi", "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
   {#rcd_define}, "rcdi" defined in {#rcdi_define}, and "crn" defined in
   {#crn_define} 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 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:

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   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" defined claims.

   If the Verification Service only understands the "shaken" PASSporT
   extension claims and doesn't support "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 [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

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   *  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 16.3.  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
   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.

15.  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.

16.  IANA Considerations

16.1.  JSON Web Token Claim

   This document 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

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   Specification Document(s): [RFCThis]

   Claim Name: "crn"

   Claim Description: Call Reason

   Change Controller: IESG

   Specification Document(s): [RFCThis]

16.2.  Personal Assertion Token (PASSporT) Extensions

   This document requests that the IANA add a new entry to the Personal
   Assertion Token (PASSporT) Extensions registry for the type "rcd"
   which is specified in [RFCThis].

16.3.  PASSporT RCD Claim Types

   This document requests that the IANA create a new registry for
   PASSporT RCD claim types.  This new registry should be added to the
   "Personal Assertion Token (PASSporT)" group.  Registration of new
   PASSporT RCD claim types shall be under the Specification Required
   policy.

   This registry is to be initially populated with five claim name
   values, "nam", "apn", "icn", "jcd", and "jcl", which are specified in
   [RFCThis].  This is a two column registry with column1 = "Name" and
   column2 = "Reference Document".  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.

17.  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 should
   follow an appropriate consistent policy defined and governed by the
   eco-system using RCD and the STIR framework.  This can be of many
   forms, depending on the setup and constraints of the policy
   requirements of the eco-system 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

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   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 in many current base communications protocols,
   for example SIP, is information that 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 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 availability in the deployment of the PKI system,
   may present a privacy issue.  The use of "rcdi" claim and digests for
   representing JWT claim contents is RECOMMENDED for the prevention of
   the exposure of that information through the certificates which are
   often publically 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 implimenting this specification.  [RFC3986] Section 7
   contains good additional guidance to consider when communicating or
   dereferencing URLs and URIs.

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17.1.  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.

18.  References

18.1.  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-06, 3 June 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-sipcore-
              callinfo-rcd-06>.

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

   [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>.

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   [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>.

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   [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>.

18.2.  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.

   [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>.

   [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>.

   [W3C-SubresourceIntegrity]
              W3C, "Subresource Integrity <https://www.w3.org/TR/SRI/>",
              23 June 2016.

Authors' Addresses

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

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

Wendt & Peterson         Expires 7 December 2023               [Page 34]