PASSporT Extension for Rich Call Data

PASSporT is a token format based on JWT 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 . The STIR problem statement declared securing the display name of callers outside of STIR’s initial scope, so baseline STIR provides no features for caller name. This specification documents an optional mechanism for PASSporT and the associated STIR procedures which extend PASSporT objects to protect additional elements conveying richer information: information that is intended to be rendered to assist a called party in determining whether to accept or trust incoming communications. This includes the name of the person or entity on one side of a communications session, the traditional “Caller ID” of the telephone network, along with related display information that would be rendered to the called party during alerting, or potentially used by an automaton to determine whether and how to alert a called party. Traditional telephone network signaling protocols have long supported delivering a ‘calling name’ from the originating side, though in practice, the terminating side is often left to derive a name from the calling party number by consulting a local address book or an external database. SIP similarly can carry this information in a ‘display-name’ in the From header field value from the originating to terminating side, or alternatively in the Call-Info header field. However, both are unsecured fields that really cannot be trusted in most interconnected SIP deployments, and therefore is a good starting point for a framework that utilizes STIR techniques and procedures for protecting call related information including but not limited to calling name. As such, the baseline use-case for this document extends PASSporT to provide cryptographic protection for the “display-name” field of SIP requests as well as further “rich call data” (RCD) about the caller, which includes the contents of the Call-Info header field or other data structures that can be added to the PASSporT. This document furthermore specifies a third-party profile that would allow external authorities to convey rich information associated with a calling number via a new type of PASSporT. Finally, this document describes how to preserve the integrity of the RCD in scenarios where there may be non-authoritative users initiating and signing RCD and therefore a constraint on the RCD data that a PASSporT can attest via certificate-level controls.

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 when, and only when, they appear in all capitals, as shown here.

The main intended use of the signing of Rich Call Data (RCD) using STIR within SIP or more generally as a PASSporT extension 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 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 , typically a textual description of the caller, or alternate presentation numbers often used in From Header field or P-Asserted-ID . The second category is a set of RCD that is defined as part of the jCard definitions or extensions to that data. 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), 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.

When incorporating call data that represents a user, even in traditional calling name services today, often there is policy and restrictions around what data is allowed to be used. Whether preventing offensive language or icons or enforcing uniqueness, potential trademark or copyright violations or other policy enforcement, there might be the desire to pre-certify or “vet” the specific use of rich call data. This document defines a mechanism that allows for a direct or indirect party that controls the policy to approve or certify the content, create a cryptographic digest that can be used to validate that data and applies a constraint in the certificate to allow the recipient and verifier to validate that the specific content of the RCD is as intended at its creation and approval or certification. There are two mechanisms that are defined to accomplish that for two distinct categories of purposes. The first of the mechanisms include the definition of an integrity claim. The RCD integrity mechanism is a process of generating a sufficiently strong cryptographic digest for each resource referenced as a claim value or as a value within a claim value by one or more globally unique URIs (e.g., an image file referenced by “jcd” or a jCard referenced by “jcl”). This mechanism is inspired by and based on the W3C Subresource Integrity specification (http://www.w3.org/TR/SRI/). The second of the mechanisms uses the capability called JWT Claim Constraints, defined in and extended in . The JWT Claim Constraints specifically guide the verifier within the certificate used to sign the PASSporT for the inclusion (or exclusion) of specific claims and their values, so that the content intended by the signer can be verified to be accurate. Both of these mechanisms, integrity digests and JWT Claims Constraints, can be used together or separately depending on the intended purpose. The first category of purpose is whether the rich call data conveyed by the RCD passport is pass-by-value or passed-by-reference; i.e., is the information contained in the passport claims and therefore integrity protected by the passport signature, or is the information contained in an external resource referenced by a URI in the RCD PASSporT. The second category of purpose is whether the signer is authoritative or has responsibility for the accuracy of the RCD based on the policies of the eco-system the RCD PASSporTs are being used. The following table provides an overview of the framework for how integrity should be used with RCD. (Auth represents authoritative in this table)

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

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

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

The “apn” key value is an optional alternate presentation number associated with the originator of personal communications, which may for example derive from the user component of the From header field value of a SIP request (in cases where a network number is carried in the P-Asserted-Identity ), or alternatively from the Additional-Identity header field value [3GPP TS 24.229 v16.7.0], or a similar field in other PASSporT using protocols. Its intended semantics are to convey a number that the originating user is authorized to show to called parties in lieu of their default number, such as cases where a remote call agent uses the main number of a call center instead of their personal telephone number. The “apn” key value is a canonicalized telephone number per 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 authorizes the use of an alternate presentation number by the user. How the signer determines that a user is authorized to present the number in question is a policy decision outside the scope of this document, however, the vetting of the alternate presentation number should follow the same level of vetting as telephone identities or any other information contained in an RCD PASSporT. This usage is intended as an alternative to conveying the presentation number in the “tel” key value of a jCard, in situations where no other rich jCard data needs to be conveyed with the call. Only one “apn” key may be present. “apn” MUST be used when it is the intent of the caller or signer to display the alternate presentation number even if “jcd” or “jcl” keys are present in a PASSporT with a “tel” key value.

The “icn” key value is an optional URI reference to an image that can be used to pictorially represent the originator of personal communications. This icon key value should be used as a base or default method of associating an image with a calling party. When being used for SIP 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 . Example as follows:

; purpose=icon ]]> Note that 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 , there are alternative ways of including photos and logos as URI references. The “icn” key should be then considered a base or default image and jCard usage should be considered for profiles and extensions that provide more direct guidance on the usage of specific defined usage of what each image type represents for the proper rendering to end users.

The “jcd” key value is defined to contain a jCard JSON object. This jCard object is intended to represent and derives from the Call-Info header field value defined in with a type of “jcard”. As also defined in , format of the jCard and properties used should follow the normative usage and formatting rules and procedures. It is an extensible object where the calling party can provide both the standard types of information defined in jCard or can use the built-in extensibility of the jCard specification to add additional information. The “jcd” key is optional. If included, this key MUST only be included once in the “rcd” JSON object and MUST NOT be included if there is a “jcl” key included. The use of “jcd” and “jcl” keys are mutually exclusive. The jCard object value for “jcd” MUST only have referenced content for URI values that do not further reference URIs. Future specifications may extend this capability, but as stated in it constrains the security properties of RCD information and the integrity of the content referenced by URIs. Note: even though we refer to as the definition of the jcard properties for usage in an “rcd” PASSporT, other future specifications and protocols are encouraged to be adapted for use of “jcd” (or similarly “jcl” below) key beyond SIP and Call-Info.

The “jcl” key value is defined to contain a URI that refers the recipient to a jCard 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 . This link may derive from the Call-Info header field value defined in with a type of “jcard”. As also defined in , format of the jCard and properties used should follow the normative usage and formatting rules and procedures. The “jcl” key is optional. If included, this key MUST only be included once in the “rcd” JSON object and MUST NOT be included if there is a “jcd” key included. The use of “jcd” and “jcl” keys are mutually exclusive. The jCard object referenced by the URI value for “jcl” MUST only have referenced content for URI values that do not further reference URIs. Future specifications may extend this capability, but as stated in it constrains the security properties of RCD information and the integrity of the content referenced by URIs.

The “rcdi” claim is included for the second and fourth modes described in the integrity overview of this document. If this claim is present it MUST be included only once with the corresponding single “rcd” claim. The value of the “rcdi” claim is a JSON object that is defined as follows. The claim value of “rcdi” claim key is a JSON object with a set of JSON key/value pairs. These objects correspond to each of the elements of the “rcd” claim object that require integrity protection with an associated digest over the content referenced by the key string. The individual digest of different elements of the “rcd” claim data and external URI referenced content is kept specifically separate to allow the ability to verify the integrity of only the elements that are ultimately retrieved or downloaded or rendered to the end-user. The key value references a specific object within the “rcd” claim value using a JSON pointer defined in with a minor additional rule to support external URI references that include JSON objects themselves, for the specific case of the use of “jcl”. JSON pointer syntax is the key value that specifies exactly the part of JSON that is used to generate the digest which produce the resulting string that makes up the value for the corresponding key. Detailed procedures are provided below, but an example “rcdi” is provided here:

The values of each key/value pair consists of a digest across either the direct values or indirectly referenced resources, combined with a string that defines the crypto algorithm used to generate the digest. RCD implementations MUST support the following hash algorithms, “SHA256”, “SHA384”, and “SHA512”. The SHA-256, SHA-384, and SHA-512 are part of the SHA-2 set of cryptographic hash functions defined by the National Institute of Standards and Technologies (NIST). Implementations MAY support additional algorithms, but MUST NOT support known weak algorithms such as MD5 or SHA-1. In the future, the list of algorithms may be re-evaluated based on security best practices. The algorithms are represented in the text by “sha256”, “sha384”, or “sha512”. The character following the algorithm string MUST be a minus character, “-“. The subsequent characters are the base64 encoded 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.

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

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

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

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:

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 zero-based array indexes are used to reference the URI strings.

The use of a JSON pointer and integrity digest for the “jcd” claim key and value is optional. The “jcd” value is the directly included jCard array and can be protected by the signature and can be constrained directly with JWTClaimConstraints. However, for data length reasons (as with “icn” above) or more importantly for potential privacy and/or security considerations with a publically accessible certificate this specification would recommend the use of the “rcdi” JSON pointer and integrity digest as the contraint value in JWTClaimConstraints over the jCare data. It is important to remember the array indexes for JSON Pointer are dependent on the order of the elements in the jCard. The use of digest for the “/jcd” corresponding to the entire jCard array string can be included as a redundant mechanism to avoid any possibility of substitution, insertion attacks, or other potential techniques that may be possible to avoid integrity detection. 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 directly part of the overall “rcd” claim JSON object. The following example illustrates a “jcl” version of the above “jcd” example.

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

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. The JSON pointer either refers 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. 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 , Section 9. The resulting string MUST be a Base64 encoded digest string (for sha256 this should result in approximately 44 characters). 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 URI referenced content is JSON formatted, follow the procedures defined in list item 2 above. Either the binary data or string content of the file is used to create a resulting string which MUST be a Base64 encoded digest string (for sha256 this should result in approximately 44 characters).

For the third mode described in the integrity overview of this document, where only JWT Claim Constraints for “rcd” claims without an “rcdi” claim is required, the procedure when creating the certificate with the intent to always include an “rcd” claim, to include a JWT Claim Constraints on inclusion of an “rcd” claim with the intended values required to be constrained by the certificate used to sign the PASSporT. The “permittedValues” for the “rcd” claim may optionally contain multiple entries, to support the case where the certificate holder is authorized to use different sets of rich call data. Only including “permittedValues” for “rcd” (with no “mustInclude”) provides the ability to either have no “rcd” claim or only the set of constrained “permittedValues” values for an included “rcd” claim.

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

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 corresponding to the “call-reason” parameter for the Call-Info header. This claim is optional.

As also noted in this claim is included as corresponding to “call-reason” Call-Info parameter, but there is an alternative suggested way to include call-reason which is to use the “cif” claim with a “call-reason” key value, as defined below in this document.

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

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

The PASSporT claims object contains the “rcd” key with its corresponding value. The value of “rcd” is an array of JSON objects, of which one, the “nam” object, is mandatory. The key syntax of “nam” follows the display-name ABNF given in . After the header and claims PASSporT objects have been constructed, their signature is generated normally per the guidance in .

An “rcd” PASSporT that uses claims defined in this specification, in order to have a successful verification outcome, MUST conform to the following: have a valid signature abide by all rules set forth in the proper construction of the claims abide by JWT Claims Constraint rules defined in Section 8 or extended in if present in the certificate used to sign the PASSporT Consistent with the verification rules of PASSporTs more generally , if any of the above criteria is not met, relying parties MUST NOT use any of the claims in the PASSporT.

If the “rcdi” claim exists, any party that dereferences a URI (i.e. downloading content for display to users) from the “rcd” claim MUST perform integrity validation of the content against the corresponding digest. Consequently, if URIs with contents covered by integrity digests are passed to another entity, the corresponding integrity digest MUST also be included, for example by passing the PASSporT. Entities that pass on the content without the URI do not have to pass on the corresponding integrity digest. An entity that does not otherwise need to dereference a URI from the “rcd” claim would be discouraged from unnecessarily dereferencing the URI solely to perform integrity verification. If there is any issue with completing the integrity verification procedures for externally referenced content, including HTTP or HTTPS errors, the referenced content MUST be considered not verified. This SHOULD NOT however impact the result of base PASSporT verification for claims content that is directly included in the claims of the PASSporT.

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

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

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.

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:

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

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

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

Compact form of a “crn” PASSporT claim shall be re-constructed using the “call-reason” parameter of a Call-Info header as defined by .

Beyond naming information and the information that can be contained in a jCard object, there may be additional human-readable information about the calling party that should be rendered to the end user in order to help the called party decide whether or not to pick up the phone. This is not limited to information about the caller, but includes information about the call itself, which may derive from analytics that determine based on call patterns or similar data if the call is likely to be one the called party wants to receive. Such data could include: information related to the location of the caller, or any organizations or institutions that the caller is associated with, or even categories of institutions (is this a government agency, or a bank, or what have you), or hyperlinks to images, such as logos or pictures of faces, or to similar external profile information, or information processed by an application before rendering it to a user, like social networking data that shows that an unknown caller is a friend-of-a-friend, or reputation scores derived from crowdsourcing, or confidence scores based on broader analytics about the caller and callee. All of these data elements would benefit from the secure attestations provided by the STIR and PASSporT frameworks. A new IANA registry has been defined to hold potential values of the “rcd” array; see . 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.

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 use cases. The manner in which third-party services are discovered is outside the scope of this document. An intermediary use case might look as follows: a SIP INVITE carries a display name in its From header field value and an initial PASSporT object without the “rcd” claim. When a terminating verification service implemented at a SIP proxy server receives this request, and determines that the signature is valid, it might query a third-party service that maps telephone numbers to calling party names. Upon receiving the PASSport in a response from that third-party service, the terminating side could add a new Identity header field to the request for the “rcd” PASSporT object provided by the third-party service. It would then forward the INVITE to the terminating user agent. If the display name in the “rcd” PASSporT object matches the display name in the INVITE, then the name would presumably be rendered to the end user by the terminating user agent. A very similar flow could be followed by an intermediary closer to the origination of the call. Presumably such a service could be implemented at an originating network in order to decouple the systems that sign for calling party numbers from the systems that provide rich data about calls. In an alternative use case, the terminating user agent might query a third-party service. In this case, no new Identity header field would be generated, though the terminating user agent might receive a PASSporT object in return from the third-party service, and use the “rcd” field in the object as a calling name to render to users while alerting. While in the traditional telephone network, the business relationship between calling customers and their telephone service providers is the ultimate root of information about a calling party’s name, some other forms of data like crowdsourced reputation scores might derive from third parties. When those elements are present, they MUST be in a third-party “rcd” PASSporT using “iss” claim described in the next section.

A third-party PASSporT contains an “iss” element to distinguish its PASSporTs from first-party PASSporTs. Third-party “rcd” PASSporTs are signed with credentials that do not have authority over the identity that appears in the “orig” element of the PASSporT claims. The presence of “iss” signifies that a different category of credential is being used to sign a PASSporT than the certificates used to sign STIR calls; it is instead a certificate that identifies the source of the “rcd” data. How those credentials are issued and managed is outside the scope of this specification; the value of “iss” however MUST reflect the Subject of the certificate used to sign a third-party PASSporT. The explicit mechanism for reflecting the subject field of the certificate is out of scope of this document and left to the certificate governance policies that define how to map the “iss” value in the PASSporT to the subject field in the certificate. Relying parties in STIR have always been left to make their own authorization decisions about whether to trust the signers of PASSporTs, and in the third-party case, where an entity has explicitly queried a service to acquire the PASSporT object, it may be some external trust or business relationship that induces the relying party to trust a PASSporT. An example of a Third Party issued PASSporT claims object is as follows.

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

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

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

;alg=ES256; ppt="rcd" ]]> This specification assumes that by default, a SIP authentication service derives the value of “rcd”, specifically only for the “nam” key value, from the display-name component of the From header field value of the request, alternatively for some calls this may come from the P-Asserted-ID header. It is however a matter of authentication service policy to decide how it populates the value of “nam” key, which MAY also derive from other fields in the request, from customer profile data, or from access to external services. If the authentication service generates an “rcd” claim containing “nam” with a value that is not equivalent to the From header field display-name value, it MUST use the full form of the PASSporT object in SIP.

Section 6.2 Step 5 requires that specifications defining “ppt” values describe any additional verifier behavior. The behavior specified for the “ppt” values of “rcd” is as follows. If the PASSporT is in compact form, then the verification service SHOULD extract the display-name from the From header field value, if any, and use that as the value for the “nam” key when it recomputes the header and claims of the PASSporT object. Additionally, if there exists a Call-Info header field as defined in , the “jcard” value can be derived to determine the “jcd” key when it recomputes the header and claims of the PASSporT object. If the signature validates over the recomputed object, then the verification should be considered successful. However, if the PASSport is in full form with a “ppt” value of “rcd”, then the verification service MUST extract the value associated with the “rcd” “nam” key in the object. If the signature validates, then the verification service can use the value of the “rcd” “nam” key as the display name of calling party, which would in turn be rendered to alerted users or otherwise leveraged in accordance with local policy. This allows SIP networks that convey the display name through a field other than the From header field to interoperate with this specification. Similarly, the “jcd” or linked “jcl” jcard information and “crn” can be optionally, based on local policy for devices that support it, used to populate a Call-Info header field following the format of . The third-party “rcd” PASSporT cases presents some new challenges, as an attacker could attempt to cut-and-paste such a third-party PASSporT into a SIP request in an effort to get the terminating user agent to render the display name or confidence values it contains to a call that should have no such assurance. A third-party “rcd” PASSporT provides no assurance that the calling party number has not been spoofed: if it is carried in a SIP request, for example, then some other PASSporT in another Identity header field value would have to carry a PASSporT attesting that. A verification service MUST determine that the calling party number shown in the “orig” of the “rcd” PASSporT corresponds to the calling party number of the call it has received, and that the “iat” field of the “rcd” PASSporT is within the date interval that the verification service would ordinarily accept for a PASSporT. Verification services may alter their authorization policies for the credentials accepted to sign PASSporTs when third parties generate PASSporT objects, per . This may include accepting a valid signature over a PASSporT even if it is signed with a credential that does not attest authority over the identity in the “orig” claim of the PASSporT, provided that the verification service has some other reason to trust the signer. No further guidance on verification service authorization policy is given here. The behavior of a SIP UAS upon receiving an INVITE containing a PASSporT object with an “rcd” claim largely remains a matter of implementation policy. In most cases, implementations would render this calling party name information to the user while alerting. Any user interface additions to express confidence in the veracity of this information are outside the scope of this specification.

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 . For cases where the entity originating the personal communications is supporting the authentication service for the calling identity and is the authority of the Rich Call Data, rather than creating multiple Identity header fields cooresponding to multiple PASSporT extensions, the authentication service can alternatively directly add the “rcd” claim to a PASSporT that authenticates the calling identity. It is critically important for the user of this specification to recognize that the certificates used must include the necessary JWT Claims Constraints and permitted values for proper integrity and security of the values in the “rcd” claim incorporated into PASSporTs that are not “rcd”. The verifier of “rcd” claims MUST recognize if the signing certificate contains no claim constraints for direct values or referenced content that they should have some sort of “trust” relationship with the signer of the PASSPorT that can vouch for or have an understanding of how the rich call data was properly vetted. An example scenario that demonstrates this might be when an “rcd” PASSporT with information that was properly vetted, integrity protected and constrained and is transferred by a middle party to another PASSporT and signed by that party without that integrity protection and constraints provided in the certificate. These scenarios lose the end-to-end trust and integrity required by this specification. However, it is recognized that some UNI or provider to device scenarios where there is an authenticated “trust” relationship MAY warrant the technique described in this section.

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.

In the case of which is the PASSporT extension supporting the SHAKEN specification , 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:

A Verification Service that supports “rcd” and “shaken” PASSporT extensions is able to receive the above PASSporT and interpret both the “shaken” claims as well as the “rcd” defined claim. If the Verification Service only understands the “shaken” PASSporT extension claims and doesn’t support “rcd” PASSporT extension, then the “rcd” claim is used during PASSporT signature validation but is otherwise ignored and disregarded.

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.

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

This specification requests that the IANA add a new entry to the PASSporT Types registry for the type “rcd” which is specified in [RFCThis].

This document requests that the IANA create a new registry for PASSporT RCD types. Registration of new PASSporT RCD types shall be under the Specification Required policy. This registry is to be initially populated with four values, “nam”, “apn”, “jcd”, and “jcl”, which are specified in [RFCThis].

Whether its identities, alternate identities, images, logos, physical addresses, all of the information contained in a RCD PASSporT must follow some form of vetting in which the authoritative entity or user of the information being signed MUST follow an applicable policy of the eco-system using RCD. This can be of many forms, depending on the setup and constraints of the eco-system so is therefore out-of-scope of this document. However, the general chain of trust that signers of RCD PASSporT are either directly authoritative or have been delegated authority through certificates using JWT Claim Constraints and integrity mechanisms defined in this and related documents is critical to maintain the integrity of the eco-system utilizing this and other STIR related specifications. Revealing information such as the name, location, and affiliation of a person necessarily entails certain privacy risks. Baseline PASSporT has no particular confidentiality requirement, as the information it signs over in a using protocol like SIP is all information that SIP carries in the clear anyway. Transport-level security can hide those SIP fields from eavesdroppers, and the same confidentiality mechanisms would protect any PASSporT(s) carried in SIP. The use of JWTClaimConstraints, a mechanism defined in and extended in to constrain any of the RCD information in the public certificate by including that information in the certificate, depending on the availbility in the deployment of the PKI system, may present a privacy issue. The use of “rcdi” claim and digests for representing JWT claim contents may be a recommended way of preventing the exposure of that information through the certificates which are often publically accessible and available. 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.

While this can apply to any PASSporT that is signed with a STIR Delegate Certificates , 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 for preventing the ability to include claims beyond the claims defined in this document may need to be considered. Certificate issuers SHOULD NOT include an entry in mustExclude for the “rcdi” claim for a certificate that will be used with the PASSporT Extension for Rich Call Data defined in this document. Excluding this claim would prevent the integrity protection mechanism from working properly.