]> Somos Inc.

chris@appliedbits.com

TransUnion

mary.ietf.barnes@gmail.com

This document extends the Personal Assertion Token (PASSporT), which is a token object that conveys cryptographically signed information about the participants involved in communications. The extension is defined based on the "Signature-based Handling of Asserted information using toKENs (SHAKEN)" specification by the ATIS/SIP[ Forum IP-NNI Task Group. It provides both (1) a specific set of levels of confidence in the correctness of the originating identity of a call originated in a SIP-based telephone network as well as (2) an identifier that allows the Service Provider (SP) to uniquely identify the origin of the call within its network. This document obsoletes RFC8588.

Introduction The Signature-based Handling of Asserted information using toKENs (SHAKEN) specification defines a framework for using Secure Telephone Identity Revisited (STIR) protocols including the Personal Assertion Token (PASSporT) , SIP Authenticated Identity Management , and the STIR certificate framework for implementing the cryptographic validation of an authorized originator of telephone calls using SIP. Because the current telephone network contains traffic originated from both VoIP and TDM/SS7 (Time Division Multiplexing / Signaling System 7), there are many scenarios that need to be accounted for where PASSporT signatures may represent either direct or indirect call origination scenarios. The SHAKEN specification defines levels of attestation of the origination of the call as well as an origination identifier that can help create a unique association between the origin of a particular call to the point in the VoIP or TDM telephone network the call came from to identify, for example, either a customer or class of service that call represents. This document specifies these values as claims to extend the base set of PASSporT claims.

Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. In addition, the following terms are used in this document:

• Verified association: Typically defined as an authenticated relationship between a customer and a device that initiated a call on behalf of that customer, for example, a subscriber account with a specific SIM card or set of SIP credentials.
• PASSporT: Defined in is a JSON Web Token defined specifically for securing the identity of an initiator of personal communication. This document defines a specific extension to PASSporT.

Overview of "shaken" PASSporT Extension The SHAKEN framework is designed to use PASSporT as a method of asserting the caller's telephone identity. In addition to the PASSporT base claims, there are two additional claims that have been defined for the needs of a service provider to signal information beyond just the telephone identity. First, in order to help bridge the transition of the state of the current telephone network (which has calls with no authentication and non-SIP signaling not compatible with the use of PASSporT and Secure Telephone Identity (STI) in general), there is an attestation claim. This provides three levels of attestation: a full attestation when the service provider can fully attest to the calling identity, a partial attestation when the service provider originated a telephone call but cannot fully attest to the calling identity, and a gateway attestation, which is the lowest level of attestation and represents the service provider receiving a call from a telephone gateway that does not support PASSporT or STI. The second claim is a unique origination identifier that should be used by the service provider to identify different sources of telephone calls to support a traceback mechanism that can be used for enforcement and identification of a source of illegitimate calls. The use of the compact form of PASSporT is not specified in this document and is not specified for use in SHAKEN . The next two sections define these new claims.

PASSporT "attest" Claim This indicator allows for both identifying the service provider that is vouching for the call as well as clearly indicating what information the service provider is attesting to. The "attest" claim can be one of the following three values: 'A', 'B', or 'C'. These values correspond to 'Full Attestation', 'Partial Attestation', and 'Gateway Attestation', respectively. See for the definitions of these three levels of attestation.

PASSporT "origid" Claim The purpose of the "origid" claim is described in . The value of "origid" claim is a Universally Unique Identifier (UUID) as defined in . Please refer to for a discussion of the privacy considerations around the use of this value.

Example "shaken" PASSporT

Using "shaken" in SIP The use of the "shaken" PASSporT type and the "attest" and "origid" claims for SIP is formally defined in using the SIP Identity header field defined in .

Order of Claim Keys The order of the claim keys MUST follow the rules of Section 9 of ; the claim keys MUST appear in lexicographic order. Therefore, the claim keys discussed in this document appear in the PASSporT Payload in the following order:

• attest
• dest
• iat
• orig
• origid

Security Considerations This document defines a new PASSporT extension. The considerations related to the security of the PASSporT object itself are the same as those described in . defines how to compare the values of the "dest", "orig", and "iat" claims against fields in a SIP message containing a PASSporT as part of validating that request. The values of the new "attest" and "origid" claims added by this extension are not used in such a validation step. They are not compared to fields in the SIP message. Instead, they simply carry additional information from the signer to the consumer of the PASSporT. This new information shares the same integrity protection and non-repudiation properties as the base claims in the PASSporT.

Privacy Considerations As detailed in Section 26 of , SIP messages inherently carry identifying information of the caller and callee. The addition of STIR cryptographically attests that the signing party vouches for the information given about the callee, as is discussed in the Privacy Considerations of . SHAKEN furthermore adds an "origid" value to the STIR PASSporT, which is an opaque unique identifier representing an element on the path of a given SIP request. This identifier is generated by an originating telephone service provider to identify where within their network (e.g. a gateway or particular service element) a call was initiated; "origid" can facilitate forensic analysis of call origins when identifying and stopping bad actors trying to spoof identities or make fraudulent calls. The opacity of the "origid" claim value is intended to minimize exposure of information about the origination of calls labeled with an "origid" value. It is therefore RECOMMENDED that implementations generate a unique "origid" value per call in such a way that only the generator of the "origid" can determine when two "origid" values represent the same or different elements. If deployed systems instead use a common or related "origid" for service elements in their network, the potential for discovering patterns through correlation of those calls exists. This could allow a recipient of calls to, for instance, learn that a set of callers are using a particular service or coming through a common gateway. It is expected that SHAKEN PASSporTs are shared only within an trust domain and will be stripped before calls exit that trust domain, but this information still could be used by analytics on intermediary and terminating systems to reveal information that could include geographic location and even device-level information, depending on how the "origid" is generated.

IANA Considerations

JSON Web Token claims IANA has updated the two claims to the "JSON Web Token Claims" registry as defined in to reference this RFC XXXX.

Claim Name: origid

Claim Description: Originating Identifier as defined in SHAKEN framework

Change Controller: IESG

Specification Document(s): RFC XXXX

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

Changes from RFC8588 This RFC replaces . The update addressees an error in the example for the "iat", which should not have any quotes. The reference is also updated to reference the version that was in effect at the time this document was published, as the ATIS standards process only retains the most version of a published specifications.

References Normative References ATIS/SIP Forum IP-NNI Task Group In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. The baseline security mechanisms in the Session Initiation Protocol (SIP) are inadequate for cryptographically assuring the identity of the end users that originate SIP requests, especially in an interdomain context. This document defines a mechanism for securely identifying originators of SIP requests. It does so by defining a SIP header field for conveying a signature used for validating the identity and for conveying a reference to the credentials of the signer. This document obsoletes RFC 4474. This document defines a method for creating and validating a token that cryptographically verifies an originating identity or, more generally, a URI or telephone number representing the originator of personal communications. The Personal Assertion Token, PASSporT, is cryptographically signed to protect the integrity of the identity of the originator and to verify the assertion of the identity information at the destination. The cryptographic signature is defined with the intention that it can confidently verify the originating persona even when the signature is sent to the destination party over an insecure channel. PASSporT is particularly useful for many personal-communications applications over IP networks and other multi-hop interconnection scenarios where the originating and destination parties may not have a direct trusted relationship. In order to prevent the impersonation of telephone numbers on the Internet, some kind of credential system needs to exist that cryptographically asserts authority over telephone numbers. This document describes the use of certificates in establishing authority over telephone numbers, as a component of a broader architecture for managing telephone numbers as identities in protocols like SIP. This document extends the Personal Assertion Token (PASSporT), which is a token object that conveys cryptographically signed information about the participants involved in communications. The extension is defined based on the "Signature-based Handling of Asserted information using toKENs (SHAKEN)" specification by the ATIS/SIP Forum IP-NNI Task Group. It provides both (1) a specific set of levels of confidence in the correctness of the originating identity of a call originated in a SIP-based telephone network as well as (2) an identifier that allows the Service Provider (SP) to uniquely dentify the origin of the call within its network. This specification defines UUIDs (Universally Unique IDentifiers) -- also known as GUIDs (Globally Unique IDentifiers) -- and a Uniform Resource Name namespace for UUIDs. A UUID is 128 bits long and is intended to guarantee uniqueness across space and time. UUIDs were originally used in the Apollo Network Computing System (NCS), later in the Open Software Foundation's (OSF's) Distributed Computing Environment (DCE), and then in Microsoft Windows platforms. This specification is derived from the OSF DCE specification with the kind permission of the OSF (now known as "The Open Group"). Information from earlier versions of the OSF DCE specification have been incorporated into this document. This document obsoletes RFC 9562. [STANDARDS-TRACK] Informative References This document describes Session Initiation Protocol (SIP), an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribution, and multimedia conferences. [STANDARDS-TRACK]

Acknowledgements The authors would like to thank those that helped review and contribute to this document including specific contributions from Jon Peterson, Russ Housley, Robert Sparks, and Andrew Jurczak. The authors would like to acknowledge the work of the ATIS/SIP Forum IP-NNI Task Force to develop the concepts behind this document.