stir C. Wendt
Internet-Draft Comcast
Intended status: Standards Track M. Barnes
Expires: March 24, 2019 iconectiv
September 20, 2018



This document extends PASSporT, which is a token object that conveys cryptographically-signed information about the participants involved in communications, to include information defined as part of the SHAKEN specification from ATIS (Alliance for Telecommunications Industry Solutions) and the SIP Forum IP-NNI Joint Task Force. These extensions provide a level of confidence in the correctness of the originating identity for a telephone network that has communications coming from both STIR participating originating communications as well as communications that does not include STIR information.

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Table of Contents

1. Introduction

The SHAKEN [ATIS-1000074] specification defines a framework for using STIR protocols including PASSporT [RFC8225], RFC4474bis [RFC8224] and the STIR certificate framework [RFC8226] for implementing the cryptographic validation of an authorized originator of telephone calls using SIP. Because the current telephone network contains both VoIP and TDM/SS7 originated traffic, there are many scenarios that need to be accounted for where PASSporT signatures may represent either direct or indirect call origination scenarios. The SHAKEN [ATIS-1000074] specification defines levels of attestation of the origination of the call as well as an origination identifier that can help create a unique association with the origination of calls from various parts of the VoIP or TDM telephone network. This document specifies these indicators as a specified PASSporT extension.

2. Terminology

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119].

3. Overview of ‘shaken’ PASSporT extension

The SHAKEN framework is designed to use PASSporT [RFC8225] as a method of asserting the telephone number calling 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 [RFC3261] 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, including 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 can not 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 non PASSporT or STI supporting telephone gateway.

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 [ATIS-1000074].

The next two sections define these new claims.

4. 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’ as defined in [ATIS-1000074].

‘A’ represents ‘Full Attestation’ where the signing provider MUST satisfy all of the following conditions:

‘B’ represents ‘Partial Attestation’ where the signing provider MUST satisfy all of the following conditions:

‘C’ represents ‘Gateway Attestation’ where the signing provider MUST satisfy all of the following conditions:

5. PASSporT ‘origid’ Claim

The purpose of the unique origination identifier is to assign an opaque identifier corresponding to the service provider-initiated calls themselves, customers, classes of devices, or other groupings that a service provider might want to use for determining things like reputation or trace back identification of customers or gateways. The value of ‘origid’ claim is a UUID as defined in [RFC4122]. SHAKEN isn’t prescriptive in the exact usage of origid other than the UUID format as a globally unique identifier representing the originator of the call to whatever granularity the PASSporT signer determines is sufficient for the ability to trace the original origination point of the call. There will likely be best practices documents that more precisely guide it’s usage in real deployments.

6. Example “shaken” PASSporT

Protected Header

7. Using ‘shaken’ in SIP

The use of the ‘shaken’ PASSporT type and the claims ‘attest’ and ‘origid’ are formally defined in [ATIS-1000074] for usage in SIP [RFC3261] aligned with the use of the identity header defined in [RFC8224].

8. Order of Claim Keys

The order of the claim keys MUST follow the rules of [RFC8225] Section 9; 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,

9. IANA Considerations

9.1. JSON Web Token claims

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

Claim Name: “attest”

Claim Description: Attestation level as defined in SHAKEN framework

Change Controller: IESG

Specification Document(s): [RFCThis]

Claim Name: “origid”

Claim Description: Originating Identifier as defined in SHAKEN framework

Change Controller: IESG

Specification Document(s): [RFCThis]

9.2. PASSporT Types

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

10. Acknowledgements

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

11. References

11.1. Normative References

[ATIS-1000074] ATIS/SIP Forum NNI Task Group, "Signature-based Handling of Asserted information using toKENs (SHAKEN)", January 2017.
[RFC4122] Leach, P., Mealling, M. and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, DOI 10.17487/RFC4122, July 2005.
[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.
[RFC8226] Peterson, J. and S. Turner, "Secure Telephone Identity Credentials: Certificates", RFC 8226, DOI 10.17487/RFC8226, February 2018.

11.2. Informative References

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

Authors' Addresses

Chris Wendt Comcast One Comcast Center Philadelphia, PA 19103, USA EMail:
Mary Barnes iconectiv EMail: