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art Identity This document extends STIR and the Authenticated Identity Management in the Session Initiation Protocol (SIP) related to error handling for STIR verification services and how they feedback errors to STIR authentication services. Specifically, the use of a Reason header field and addressing scenarios that use multiple identity headers where some may have errors and others may not and the handling of those situations is defined.

in Section 6.2.2 discusses future specifications for enhancement of how errors are communicated and the handling of multiple Identity header fields. This specification provides some additional mechanisms for solutions to address these problems. In some deployments of STIR and specifically using SIP as defined by , one issue with the current error handling, specifically with the use of the defined 4xx error responses, is that when an error occurs with the verification of the Identity header filed or the PASSporT contained in the Identity header field and a 4xx response is returned, the call is then terminated. It may be the case that the policy for handling errors dictates that calls should continue even if there is a verification error, in the case of, for example inadvertent errors, however the authentication service should still be notified of the error so that corrective action can be taken. This specification will discuss the use of the Reason header field in subsequent provisional (1xx) responses in order to accomplish this. For the handling of multiple Identity header fields and the potential situation that some of the Identity header fields in a call may pass verification but others may have errors, this document provides a mechanism to add an identifier so that the authentication service can identify which Identity header field is being referred to in the case of an error.

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 cases where local policy dictates that a call should continue irregardless when any verification errors, including 4XX errors described in Section 6.2.2, then the verification service SHOULD not send the 4XX as a response, but rather include the error response code and reason phrase in a Reason header field, defined in , in the next provisional or final responses sent to the authentication service. Example Reason header field:

In cases where a SIP message includes multiple Identity header fields and one of those Identity header fields has an error, the verification service SHOULD include the error response code and reason phrase associated with the error in a Reason header field, defined in , in the next provisional or final responses sent to the authentication service. The reason cause in the Reason header field SHOULD represent the error that occurred when verifying the contents of the Identity header field. The association of a Reason header field and error to a specific Identity header field is accomplished by adding a “ppt” parameter containing the PASSporT that generated the error to the Reason header field. The “ppt” parameter for the Reason header field is optional, but RECOMMENDED, in particular for cases that a SIP INVITE contains multiple Identity header fields. The PASSporT can be included in full form, or optionally in compact form, where only the signature of the PASSporT is used to identify the reported Identity header field with an error. Example Reason header field with full form PASSporT:

Example Reason header field with compact form PASSporT: ~~~~~~~~~~~ Reason: SIP ;cause=436 ;text=”Bad Identity Info” ;ppt= \ “..rq3pjT1akEGjHCnWSwUnshd0-zJ6F1VOgFWSjHBr8Qjpjlk-cpFYpFYs \ ojNCpTzO3QfPOlckGaS6hEck7w” ~~~~~~~~~~~

This specification updates in that for STIR applications the use of multiple Reason header fields with the same “SIP” protocol string is allowed. So, if there is multiple Identity header field verification errors being reported the verification service SHOULD include corresponding Reason header fields with “ppt” parameters including full or compact form of the PASSporT with cause and text parameters identifying each error. Example Reason header fields for two identity info errors:

When an Authentication Service receives the Reason header field with a PASSporT it generated as part of an Identity header field and the authentication of a call, it should first follow local policy to recognize and acknowledge the error (e.g. perform operational actions like logging or alarming), but then MUST remove the identified Reason header field to avoid the PASSporT information going upstream to UAC or UAS that may not be authorized to see claim information contained in the PASSporT for privacy or other reasons.

Would like to thank David Hancock for help to identify these error scenarios and Jon Peterson, Roman Shpount, and STIR working group for helpful feedback and discussion.

TBD

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] The REGISTER function is used in a Session Initiation Protocol (SIP) system primarily to associate a temporary contact address with an address-of-record. This contact is generally in the form of a Uniform Resource Identifier (URI), such as Contact: <sip:alice@pc33.atlanta.com> and is generally dynamic and associated with the IP address or hostname of the SIP User Agent (UA). The problem is that network topology may have one or more SIP proxies between the UA and the registrar, such that any request traveling from the user's home network to the registered UA must traverse these proxies. The REGISTER method does not give us a mechanism to discover and record this sequence of proxies in the registrar for future use. This document defines an extension header field, "Path" which provides such a mechanism. [STANDARDS-TRACK] 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. 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.