Network Working Group                                           C. Wendt
Internet-Draft                                                   Comcast
Intended status: Standards Track                             J. Peterson
Expires: August 26, 2021                                    Neustar Inc.
                                                       February 22, 2021

                 PASSporT Extension for Rich Call Data


   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 users.  This framework is intended to extend
   caller and call specific information beyond human-readable display
   name comparable to the "Caller ID" function common on the telephone
   network.  The JSON element defined for this purpose, Rich Call Data
   (RCD), is an extensible object defined to either be used as part of
   STIR or with SIP Call-Info to include related information about calls
   that helps people decide whether to pick up the phone.  This signing
   of the RCD information is also enhanced with a integrity mechanism
   that is designed to protect the authoring and transport of this
   information between authoritative and non-authoritative parties
   generating and signing the Rich Call Data for support of different
   usage and content policies.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 26, 2021.

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Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   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 Claims . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  PASSporT "rcd" Claim  . . . . . . . . . . . . . . . . . .   6
       5.1.1.  "nam" key . . . . . . . . . . . . . . . . . . . . . .   7
       5.1.2.  "jcd" key . . . . . . . . . . . . . . . . . . . . . .   7
       5.1.3.  "jcl" key . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  "rcdi" RCD Integrity Claim  . . . . . . . . . . . . . . .   8
       5.2.1.  Creation of the "rcd" element digests . . . . . . . .   9
       5.2.2.  JWT Claim Constraint for "rcd" claims only  . . . . .  12
       5.2.3.  JWT Claim Constraint for "rcd" and "rcdi" claims  . .  12
     5.3.  PASSporT "crn" claim - Call Reason  . . . . . . . . . . .  13
       5.3.1.  JWT Constraint for "crn" claim  . . . . . . . . . . .  13
   6.  "rcd" and "crn" Claims Usage  . . . . . . . . . . . . . . . .  13
     6.1.  Example "rcd" PASSporTs . . . . . . . . . . . . . . . . .  14
   7.  Compact form of "rcd" PASSporT  . . . . . . . . . . . . . . .  15
     7.1.  Compact form of the "rcd" PASSporT claim  . . . . . . . .  15
     7.2.  Compact form of the "rcdi" PASSporT claim . . . . . . . .  16
     7.3.  Compact form of the "crn" PASSporT claim  . . . . . . . .  16
   8.  Further Information Associated with Callers . . . . . . . . .  16
   9.  Third-Party Uses  . . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  Signing as a Third Party  . . . . . . . . . . . . . . . .  18
   10. Levels of Assurance . . . . . . . . . . . . . . . . . . . . .  19
   11. Using "rcd" in SIP  . . . . . . . . . . . . . . . . . . . . .  19
     11.1.  Authentication Service Behavior  . . . . . . . . . . . .  19
     11.2.  Verification Service Behavior  . . . . . . . . . . . . .  20
   12. Using "rcd" as additional claims to other PASSporT extensions  21
     12.1.  Procedures for applying "rcd" as claims only . . . . . .  22
     12.2.  Example for applying "rcd" as claims only  . . . . . . .  22

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   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  23
   14. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
     14.1.  JSON Web Token Claim . . . . . . . . . . . . . . . . . .  23
     14.2.  PASSporT Types . . . . . . . . . . . . . . . . . . . . .  23
     14.3.  PASSporT RCD Types . . . . . . . . . . . . . . . . . . .  24
   15. Security Considerations . . . . . . . . . . . . . . . . . . .  24
     15.1.  The use of JWT Claim Constraints in delegate
            certificates to exclude unauthorized Claims  . . . . . .  24
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     16.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   PASSporT [RFC8225] is a token format based on JWT [RFC7519] for
   conveying cryptographically-signed information about the parties
   involved in personal communications; it is used to convey a signed
   assertion of the identity of the participants in real-time
   communications established via a protocol like SIP [RFC8224].  The
   STIR problem statement [RFC7340] declared securing the display name
   of callers outside of STIR's initial scope, so baseline STIR provides
   no features for caller name.  This specification documents an
   optional mechanism for PASSporT and the associated STIR procedures
   which extend PASSporT objects to protect additional elements
   conveying richer information: information that is intended to be
   rendered to an end user to assist a called party in determining
   whether to accept or trust incoming communications.  This includes
   the name of the person on one side of a communications session, the
   traditional "Caller ID" of the telephone network, along with related
   display information that would be rendered to the called party during
   alerting, or potentially used by an automaton to determine whether
   and how to alert a called party.

   Traditional telephone network signaling protocols have long supported
   delivering a 'calling name' from the originating side, though in
   practice, the terminating side is often left to derive a name from
   the calling party number by consulting a local address book or an
   external database.  SIP similarly can carry this information in a
   'display-name' in the From header field value from the originating to
   terminating side, or alternatively in the Call-Info header field.
   However, both are unsecured fields that really cannot be trusted in
   most interconnected SIP deployments, and therefore is a good starting
   point for a framework that utilizes STIR techniques and procedures
   for protecting call related information including but not limited to
   calling name.

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

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
   described in [RFC2119] and [RFC6919].

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

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

   The RCD 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.  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 a "rcd" claim defined in this document.

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

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4.  Overview of Rich Call Data Integrity

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

   There are two mechanisms that will be defined to accomplish that for
   two distinct categories of purposes.  The first of the mechanisms
   include the definition of an integrity claim.  The RCD integrity
   mechanism is a process of generating a sufficiently strong
   cryptographic digest for both the "rcd" claim contents (e.g. "nam",
   "jcd", "jcl") defined below and the resources defined by one or more
   globally unique HTTPS URLs referenced by the contents (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 (  The second of the
   mechanisms uses the capability called JWT Claim Constraints, defined
   in [RFC8226] and extended in [I-D.housley-stir-enhance-rfc8226].  The
   JWT Claim Constraints specifically guide the verifier within the
   certificate used to sign the PASSporT for the inclusion (or
   exclusion) of specific claims and their values, so that the content
   intended by the signer can be verified to be accurate.

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

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

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

   The first and simplest mode is exclusively for when all RCD content
   is directly included as part of the claims (i.e. no external
   reference URIs are included in the content, for example, "photo" or
   "logo" properties that aren't directly encoded into the JSON of the
   jCard) 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 a "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 mode cover cases where there is a different
   authoritative entity responsible for the content of the RCD, separate
   from the signer of the PASSporT itself, allowing the ability to have
   forward control at the time of the creation of the certificate of the
   allowed or vetted content included in or referenced by the RCD claim
   contents.  The primary framework for allowing the separation of
   authority and the signing of PASSporTs by non-authorized entities is
   detailed in [I-D.ietf-stir-cert-delegation] although other cases may
   apply.  As with the first and second modes, the third and fourth
   modes differ with the absence or inclusion of externally referenced
   content using URIs.

5.  PASSporT Claims

5.1.  PASSporT "rcd" Claim

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

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5.1.1.  "nam" key

   The "nam" key value is a display name, associated with the originator
   of personal communications, which may for example derive from the
   display-name component of the From header field value of a SIP
   request or alternatively from the P-Asserted-Identity header field
   value, or a similar field in other PASSporT using protocols.  This
   key MUST be included once and MUST be included as part of the "rcd"
   claim value JSON object.  If there is no string associated with a
   display name, the claim value SHOULD then be an empty string.

5.1.2.  "jcd" key

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

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

5.1.3.  "jcl" key

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

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5.2.  "rcdi" RCD Integrity Claim

   The "rcdi" claim is claim that MUST be included for the second and
   fourth modes described in integrity overview section of this
   document.  If this claim is present it MUST be only included once
   with a corresponding single "rcd" claim.  The value of the "rcdi" key
   pair 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 will correspond to each of the
   elements of the "rcd" claim object that require integrity protection
   with an associated digest over the content referenced by the key
   string.  The individual digest of different elements of the "rcd"
   claim data and external URI referenced content is kept specifically
   separate to allow the ability to verify the integrity of only the
   elements that are ultimately retrieved or downloaded or rendered to
   the end-user.

   The key value will reference a specific object within the "rcd" claim
   value using a JSON pointer defined in [RFC6901] with a minor
   additional rule to support external URI references that include JSON
   objects themselves, in particular for the specific case of the use of
   "jcl".  JSON pointer syntax is the key value that specifies exactly
   the part of JSON that should be used to generate the digest which
   will be 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" : {
     "/jcd": "sha256-H8BRh8j48O9oAZzq6A9RINQZngK7T62em8MUt1FLm52",
     "/jcd/1/2/3": "sha256-AZzq6A9RINQZngK7T62em8MUt1FLm52H8BRh8j48O9o"

   The values of each key pair are a digest combined with a string that
   defines the crypto algorithm used to generate the digest.  For RCD,
   implementations MUST support the following hash algorithms, "SHA256",
   "SHA384", or "SHA512".  The SHA-256, SHA-384, and SHA-512 are part of
   the SHA-2 set of cryptographic hash functions defined by the NIST.
   Implementations MAY support additional algorithms, but MUST NOT
   support known weak algorithms such as MD5 or SHA-1.  In the future,
   the list of algorithms may be re-evaluated based on security best
   practices.  The algorithms MUST be represented in the text by
   "sha256", "sha384", or "sha512".  The character following the
   algorithm string MUST be a minus character, "-".  The subsequent
   characters MUST be the base64 encoded digest of a canonicalized and
   concatenated string based on the JSON pointer referenced elements of
   "rcd" claim or the URI referenced content contained in the claim.

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   The details of the determination of the input string used to
   determine the digest are defined in the next section.

5.2.1.  Creation of the "rcd" element digests

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

   In the case of "nam", the only allowed value is a "string".  In order
   to reference the "nam" string value for a digest, the JSON pointer
   string would be "/nam" and the digest string would be created using
   only the string pointed to by that "/nam" following the rules of JSON

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

   As example, for the following "rcd" claim:

   "rcd": {
     "nam": "Q Branch Spy Gadgets",
     "jcd": ["vcard",
       [ ["version",{},"text","4.0"],
         ["fn",{},"text","Q Branch"],
         ["org",{},"text","MI6;Q Branch Spy Gadgets"],

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

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   "rcdi": {
     "/jcd": "sha256-30SFLGHL40498527",
     "/jcd/1/3/3": "sha256-12938918VNJDSNCJ",
     "/jcd/1/4/3": "sha256-VNJDSNCJ12938918",
     "/jcd/1/5/3": "sha256-4049852730SFLGHL"

   For the use of JSON pointer in "jcd" and because array indexes are
   dependent on the order of the elements in the jCard, the digest for
   the "/jcd" corresponding to the entire jCard array string MUST be
   included to avoid any possibility of substitution or insertion
   attacks that may be possible to avoid integrity detection, even
   though unlikely.  Each URI referenced in the jCard array string MUST
   have a corresponding JSON pointer string key and digest value.

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

   "rcd": {
     "nam": "Q Branch Spy Gadgets",
     "jcl": ""
   "rcdi": {
     "/jcl": "sha256-30SFLGHL40498527",
     "/jcl/1/3/3": "sha256-12938918VNJDSNCJ",
     "/jcl/1/4/3": "sha256-VNJDSNCJ12938918",
     "/jcl/1/5/3": "sha256-4049852730SFLGHL"

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     [ ["version",{},"text","4.0"],
       ["fn",{},"text","Q Branch"],
       ["org",{},"text","MI6;Q Branch Spy Gadgets"]

   In order to facilitate proper verification of the digest 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, it should verify 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 will either refer to an element that is a part
       or whole of a JSON object string or to a string that is a URI
       referencing an external resource.

   2.  For a JSON formatted string, serialize the element 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 used to create the digest.

   3.  For any URI referenced content, the content can either be a
       string as in jCard JSON objects or binary content.  For example,
       image and audio files contain binary content.  If the content is
       binary format it should be Base64 encoded to create a string,
       otherwise the direct string content of the file is used to create
       the digest.

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5.2.2.  JWT Claim Constraint for "rcd" claims only

   For the third mode described in the integrity overview section of
   this document, where only JWT Claim Constraint for "rcd" claims,
   without an "rcdi" claim, is required, the procedure should be, when
   creating the certificate to include a constraint on inclusion of the
   "rcd" claim as well as the contents of that claim.

   The certificate JWT Claims Constraint MUST include the following:

   o  a "mustInclude" for the "rcd" claim and a "permittedValues" equal
      to the created "rcd" claim value string.

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

5.2.3.  JWT Claim Constraint for "rcd" and "rcdi" claims

   For the fourth mode described in the integrity overview section of
   this document, if the signing of an "rcdi" claim is required to be
   protected by the authoritative certificate creator using JWT
   Constraints in the certificate, the procedure which is intended to
   constrain the signer to construct the "rcd" and "rcdi" claims and
   reference external content via URI in a pre-determined way.  Once
   both the contents of the "rcd" claim and any linked content is
   certified and the construction of the "rcdi" claim is complete, the
   "rcdi" claim is linked to the STIR certificate associated with the
   signature in the PASSporT via JWT Claim Constraints as defined in
   [RFC8226] Section 8.  It should be recognized that the "rcdi" set of
   digests is intended to be unique for only a specific combination of
   "rcd" content and URI referenced external content.

   The certificate JWT Claims Constraint MUST include both of the

   o  a "mustInclude" for the "rcd" claim, which simply constrains the
      fact that an "rcd" should be included if there is a "rcdi"

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

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

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5.3.  PASSporT "crn" claim - Call Reason

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

   Example "crn" claim with "rcd":
   "rcd": { "nam": "James Bond",
            "jcl": ""},
   "crn" : "For your ears only"

5.3.1.  JWT Constraint for "crn" claim

   The integrity of the "crn" claim can optionally be protected by the
   authoritative certificate creator using JWT Constraints in the
   certificate.  If this protection is used, a "mustInclude" for the
   "rcdi" claim and a "permittedValues" equal to the "crn" claim value
   string SHOULD be included.

6.  "rcd" and "crn" Claims Usage

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

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

   The PASSporT claims object will then contain the "rcd" key with its
   corresponding value.  The value of "rcd" is an array of JSON objects,
   of which one, the "nam" object, is mandatory.  The key syntax of
   "nam" follows the display-name ABNF given in [RFC3261].

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

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6.1.  Example "rcd" PASSporTs

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

   {  "orig":{"tn":"12025551000"},
      "rcd":{"nam":"James Bond"} }

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

   {  "orig":{"tn":"12025551000"},
      "rcd":{"nam":"James Bond"},
      "rcdi":{"/nam": "sha256-918VNJD12938SNCJ"}

   An example of a "rcd" claims object that includes the "jcd" and also
   contains a URI which requires the inclusion of an "rcdi" claim.

     "orig": { "tn": "12025551000"},
     "dest": { "tn": ["12155551001"]},
     "iat": 1443208345,
     "rcd": {
       "nam": "Q Branch Spy Gadgets",
       "jcd": ["vcard",
       [ ["version",{},"text","4.0"],
         ["fn",{},"text","Q Branch"],
         ["org",{},"text","MI6;Q Branch Spy Gadgets"],
       ] ]
     "crn": "Rendezvous for Little Nellie",
     "rcdi": {
       "/nam": "sha256-918VNJD12938SNCJ",
       "/jcd": "sha256-VNJDSNCJ12938918",
       "/jcd/1/3/3": "sha256-12938918VNJDSNCJ",
       "/jcd/1/4/3": "sha256-VNJDSNCJ12938918",
       "/jcd/1/5/3": "sha256-4049852730SFLGHL"

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   In an example PASSporT where a jCard is linked via HTTPS URL and
   "jcl" a jCard file served at a particular URL will be created.

   An example jCard JSON file is shown as follows:
     [ ["version",{},"text","4.0"],
       ["fn",{},"text","Q Branch"],
       ["org",{},"text","MI6;Q Branch Spy Gadgets"],

   If that jCard is hosted at the example address of
   "", the corresponding PASSporT claims
   object would be as follows:

     "orig": {"tn": "12025551000"},
     "dest": {"tn": ["12155551001"]},
     "iat": 1443208345,
     "rcd": {
       "nam": "Q Branch Spy Gadgets",
       "jcl": ""
     "crn": "Rendezvous for Little Nellie",
     "rcdi": {
       "/nam": "sha256-918VNJD12938SNCJ",
       "/jcl": "sha256-VNJDSNCJ12938918",
       "/jcl/1/3/3": "sha256-12938918VNJDSNCJ",
       "/jcl/1/4/3": "sha256-VNJDSNCJ12938918",
       "/jcl/1/5/3": "sha256-4049852730SFLGHL"

7.  Compact form of "rcd" PASSporT

7.1.  Compact form of the "rcd" PASSporT claim

   Compact form of an "rcd" PASSporT claim has some restrictions but
   mainly follows standard PASSporT compact form procedures.  For re-
   construction of the "nam" claim the string for the display-name in
   the From header field.  For re-construction of the "jcl", the Call-
   Info header as with purpose "jcard" defined in

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   [I-D.ietf-sipcore-callinfo-rcd] MUST be used. "jcd" claim MAY NOT be
   used as part of compact form.

7.2.  Compact form of the "rcdi" PASSporT claim

   Compact form of an "rcdi" PASSPorT claim is not supported, so if
   "rcdi" is required compact form should not be used.

7.3.  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

8.  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:

   o  information related to the location of the caller, or

   o  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

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

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

   All of these data elements would benefit from the secure attestations
   provided by the STIR and PASSporT frameworks.  A new IANA registry
   has been defined to hold potential values of the "rcd" array; see
   Section 14.3.  Specific extensions to the "rcd" PASSporT claim are
   left for future specification.

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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.  It is more likely that when those elements are
   present, they will be in a third-party "rcd" PASSporT.

9.  Third-Party Uses

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

   In telephone operations today, a third-party information service is
   commonly queried with the calling party's number in order to learn
   the name of the calling party, and potentially other helpful
   information could also be passed over that interface.  The value of
   using a PASSporT to convey this information from third parties lies
   largely in the preservation of the third party's signature over the
   data, and the potential for the PASSporT to be conveyed from
   intermediaries to endpoint devices.  Effectively, these use cases
   form a sub-case of out-of-band [I-D.ietf-stir-oob] use cases.  The
   manner in which third-party services are discovered is outside the
   scope of this document.

   An intermediary use case might look as follows: a SIP INVITE carries
   a display name in its From header field value and an initial PASSporT
   object without the "rcd" claim.  When a terminating verification
   service implemented at a SIP proxy server receives this request, and
   determines that the signature is valid, it might query a third-party
   service that maps telephone numbers to calling party names.  Upon
   receiving the PASSport in a response from that third-party service,
   the terminating side could add a new Identity header field to the
   request for the "rcd" PASSporT object provided by the third-party
   service.  It would then forward the INVITE to the terminating user
   agent.  If the display name in the "rcd" PASSporT object matches the

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   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

9.1.  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
   will necessarily be signed with credentials that do not have
   authority over the identity that appears in the "orig" element of the
   PASSporT claims.  The presence of "iss" signifies that a different
   category of credential is being used to sign a PASSporT than the
   [RFC8226] certificates used to sign STIR calls; it is instead a
   certificate that identifies the source of the "rcd" data.  How those
   credentials are issued and managed is outside the scope of this
   specification; the value of "iss" however MUST reflect the Subject
   Name field of the certificate used to sign a third-party PASSporT.
   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

   {  "orig":{"tn":"12025551000"},
      "iss":"Example, Inc.",
      "rcd":{"nam":"James Bond"} }

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10.  Levels of Assurance

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

11.  Using "rcd" in SIP

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

11.1.  Authentication Service Behavior

   An authentication service creating a PASSporT containing a "rcd"
   claim MAY include a "ppt" for "rcd" or not.  Third-party
   authentication services following the behavior in Section 9.1 MUST
   include a "ppt" of "rcd".  If "ppt" does contain a "rcd", then any
   SIP authentication services MUST add a "ppt" parameter to the
   Identity header containing that PASSporT with a value of "rcd".  The
   resulting Identity header might look as follows:

   Identity: sv5CTo05KqpSmtHt3dcEiO/1CWTSZtnG3iV+1nmurLXV/HmtyNS7Ltrg9
          w0Lu5csIppPqOg1uXndzHbG7mR6Rl9BnUhHufVRbp51Mn3w0gfUs=; \

   This specification assumes that by default, a SIP authentication
   service will derive 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

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   come from the P-Asserted-ID header.  It is however a matter of
   authentication service policy to decide how it populates the value of
   "rcd" and "nam" key, which MAY also derive from other fields in the
   request, from customer profile data, or from access to external
   services.  If the authentication service generates a PASSporT object
   containing "rcd" with a value that is not equivalent to the From
   header field display-name value, it MUST use the full form of the
   PASSporT object in SIP.

11.2.  Verification Service Behavior

   [RFC8224] Section 6.2 Step 5 requires that specifications defining
   "ppt" values describe any additional verifier behavior.  The behavior
   specified for the "ppt" values of "rcd" is as follows.  If the
   PASSporT is in compact form, then the verification service SHOULD
   extract the display-name from the From header field value, if any,
   and use that as the value for the "nam" key when it recomputes the
   header and claims of the PASSporT object.  Optionally, if there
   exists a Call-Info header field as defined in
   [I-D.ietf-sipcore-callinfo-rcd], the "jcard" value can be derived to
   determine the "jcd" key when it recomputes the header and claims of
   the PASSporT object.  If the signature validates over the recomputed
   object, then the verification should be considered successful.

   However, if the PASSport is in full form with a "ppt" value of "rcd",
   then the verification service MUST extract the value associated with
   the "rcd" "nam" key in the object.  If the signature validates, then
   the verification service can use the value of the "rcd" "nam" key as
   the display name of calling party, which would in turn be rendered to
   alerted users or otherwise leveraged in accordance with local policy.
   This will allow SIP networks that convey the display name through a
   field other than the From header field to interoperate with this
   specification.  Similarly, the "jcd" or linked "jcl" jcard
   information and "crn" can be optionally, based on local policy for
   devices that support it, used to populate a Call-Info header field
   following the format of [I-D.ietf-sipcore-callinfo-rcd].

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

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   has received, and that the "iat" field of the "rcd" PASSporT is
   within the date interval that the verification service would
   ordinarily accept for a PASSporT.

   Verification services may alter their authorization policies for the
   credentials accepted to sign PASSporTs when third parties generate
   PASSporT objects, per Section 9.1.  This may include accepting a
   valid signature over a PASSporT even if it is signed with a
   credential that does not attest authority over the identity in the
   "orig" claim of the PASSporT, provided that the verification service
   has some other reason to trust the signer.  No further guidance on
   verification service authorization policy is given here.

   The behavior of a SIP UAS upon receiving an INVITE containing a
   PASSporT object with a "rcd" claim will largely remain a matter of
   implementation policy.  In most cases, implementations would render
   this calling party name information to the user while alerting.  Any
   user interface additions to express confidence in the veracity of
   this information are outside the scope of this specification.

12.  Using "rcd" as additional claims to other PASSporT extensions

   Rich Call Data, including calling name information, for example, is
   often data that is additive data 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
   that is originating the personal communications and additionally is
   supporting the authentication service and also is the authority of
   the Rich Call Data, rather than creating multiple identity headers
   with multiple PASSporT extensions or defining multiple combinations
   and permutations of PASSporT extension definitions, the
   authentication service can alternatively directly add the "rcd"
   claims to the PASSporT it is creating, whether it is constructed with
   a PASSporT extension or not.

   Note: There is one very important caveat to this capability, because
   generally if there is URI referenced content in an "rcd" PASSporT
   there is often the requirement to use "rcdi" and JWT Claims
   Constraints.  So, it is important for the user of this specification
   to recognize that the certificates used must include the necessary
   JWT Claims Constraints for proper integrity and security of the
   values in the "rcd" claim incorporated into PASSporTs that are not

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12.1.  Procedures for applying "rcd" as claims only

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

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

12.2.  Example for applying "rcd" as claims only

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

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

   Protected Header
      "rcd":{"nam":"James Bond"}

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

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   If the Verification Service only understands the "shaken" extension
   claims but doesn't support "rcd", the "rcd" can simply be ignored and

13.  Acknowledgements

   We would like to thank David Hancock, Robert Sparks, Russ Housley,
   Eric Burger, and Alec Fenichel for helpful suggestions and comments.

14.  IANA Considerations

14.1.  JSON Web Token Claim

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

   Claim Name: "rcd"

   Claim Description: Rich Call Data Information

   Change Controller: IESG

   Specification Document(s): [RFCThis]

   Claim Name: "rcdi"

   Claim Description: Rich Call Data Integrity Information

   Change Controller: IESG

   Specification Document(s): [RFCThis]

   Claim Name: "crn"

   Claim Description: Call Reason

   Change Controller: IESG

   Specification Document(s): [RFCThis]

14.2.  PASSporT Types

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

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14.3.  PASSporT RCD Types

   This document requests that the IANA create a new registry for
   PASSporT RCD types.  Registration of new PASSporT RCD types shall be
   under the Specification Required policy.

   This registry is to be initially populated with three values, "nam",
   "jcd", and "jcl", which are specified in [RFCThis].

15.  Security Considerations

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

15.1.  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 [I-D.ietf-stir-cert-delegation], 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 [I-D.housley-stir-enhance-rfc8226]
   for preventing the ability to include claims beyond the claims
   defined in this document may need to be considered.

16.  References

16.1.  Normative References

              Housley, R., "Enhanced JWT Claim Constraints for STIR
              Certificates", draft-housley-stir-enhance-rfc8226-00 (work
              in progress), January 2021.

              Wendt, C. and J. Peterson, "SIP Call-Info Parameters for
              Rich Call Data", draft-ietf-sipcore-callinfo-rcd-01 (work
              in progress), November 2020.

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              Peterson, J., "STIR Certificate Delegation", draft-ietf-
              stir-cert-delegation-03 (work in progress), July 2020.

   [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,

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627,
              DOI 10.17487/RFC4627, July 2006,

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,

   [RFC6919]  Barnes, R., Kent, S., and E. Rescorla, "Further Key Words
              for Use in RFCs to Indicate Requirement Levels", RFC 6919,
              DOI 10.17487/RFC6919, April 2013,

   [RFC7095]  Kewisch, P., "jCard: The JSON Format for vCard", RFC 7095,
              DOI 10.17487/RFC7095, January 2014,

   [RFC7340]  Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
              Telephone Identity Problem Statement and Requirements",
              RFC 7340, DOI 10.17487/RFC7340, September 2014,

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,

   [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,

   [RFC8225]  Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
              Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,

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Internet-Draft                     RCD                     February 2021

   [RFC8226]  Peterson, J. and S. Turner, "Secure Telephone Identity
              Credentials: Certificates", RFC 8226,
              DOI 10.17487/RFC8226, February 2018,

   [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,

16.2.  Informative References

              ATIS/SIP Forum NNI Task Group, "Signature-based Handling
              of Asserted information using toKENs (SHAKEN)
              download.php/32237/ATIS-1000074.pdf>", January 2017.

              Rescorla, E. and J. Peterson, "STIR Out-of-Band
              Architecture and Use Cases", draft-ietf-stir-oob-07 (work
              in progress), March 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

Authors' Addresses

   Chris Wendt
   Comcast Technology Center
   Philadelphia, PA  19103


   Jon Peterson
   Neustar Inc.
   1800 Sutter St Suite 570
   Concord, CA  94520


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