Identity Header Errors Handling for STIR
draft-ietf-stir-identity-header-errors-handling-06

STIR Working Group                                              C. Wendt
Internet-Draft                                                Somos Inc.
Intended status: Standards Track                         6 November 2022
Expires: 10 May 2023

                Identity Header Errors Handling for STIR
           draft-ietf-stir-identity-header-errors-handling-06

Abstract

   This document extends STIR and the Authenticated Identity Management
   in the Session Initiation Protocol (SIP) error handling procedures to
   include the mapping of verification failure reasons to STIR defined
   4xx codes so the failure reason of an Identity header field can be
   conveyed to the upstream authentication service when local policy
   dictates that the call should continue in the presence of a
   verification failure.  This document also defines procedures that
   enable a failure reason to be mapped to a specific Identity header
   for scenarios that use multiple Identity header fields where some may
   have errors and others may not and the handling of those situations
   is defined.

Status of This Memo

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Reason header field protocol "STIR" . . . . . . . . . . . . .   3
   4.  Use of provisional response to signal errors without
           terminating the call  . . . . . . . . . . . . . . . . . .   4
   5.  Handling of a verification error when there are multiple
           Identity header fields  . . . . . . . . . . . . . . . . .   4
   6.  Handling multiple verification errors . . . . . . . . . . . .   5
   7.  Removal of the Reason header field by Authentication
           Service . . . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The STIR framework as described in [RFC7340] is an authentication
   framework for asserting a telephone number or URI based identity
   using a digital signature and certificate based framework as
   described in [RFC8225] and [RFC8226] respectively.  [RFC8224]
   describes the use of the STIR framework in the SIP protocol [RFC3261]
   and defines both the authentication service that creates a PASSporT,
   defined in [RFC8225], and delivers it in an Identity header field and
   the verification service that correspondingly verifies the PASSporT
   and embedded originating identity.

   This document is concerned with errors in validating PASSporTs and
   Identity header fields and how they are communicated in special
   cases.  Specifically, [RFC8224] 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
   defines a solution to help address the potential issue of multiple
   Identity headers verification errors.  Additionally, it addresses the
   issue of the current 4xx error response and that when there is a
   verification error, the call is terminated.  In some deployments, it
   may be the case that the policy for handling errors dictates that

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   calls should continue even if there is a verification error.  In many
   cases of, for example, inadvertent or operational errors that do not
   represent any identity falsification type of attempt, the policy of
   continuing the call even though the identity is not verified, may be
   the preferred policy.  In these cases, the authentication service
   should still be notified of the error so that corrective action can
   be taken to fix any issues.  This specification will discuss the use
   of the Reason header field in subsequent provisional (1xx) responses
   in order to deliver the error back to the authentication service or
   other SIP path network equipment responsible for error handling.

   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 defines the
   method of adding an identifier so that the authentication service can
   uniquely identify which Identity header field is being referred to in
   the case of an error.

2.  Terminology

   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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Reason header field protocol "STIR"

   This document defines a new Reason header field [RFC3326] protocol
   "STIR" for STIR applications using SIP as defined in [RFC8224].  The
   use of "STIR" as a reason header field protocol with the [RFC8224]
   defined error cause codes allows the use of multiple Reason header
   fields defined in [RFC3326] and updated in
   [I-D.ietf-sipcore-multiple-reasons].  Any provisional SIP Response
   message or final response message, with the exception of a 100
   (Trying), MAY contain one or more Reason header fields with a STIR
   related cause code defined in [RFC8224] or future specifications.
   The use of multiple Reason header field is discussed in more detail
   later in the document.

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4.  Use of provisional response to signal errors without terminating the
    call

   In cases where local policy dictates that a call should continue
   regardless of any verification errors that may have occured,
   including 4XX errors described in [RFC8224] 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 [RFC3326], in the next provisional or final
   responses sent to the authentication service.

   Example Reason header field:

   Reason: STIR ;cause=436 ;text="Bad Identity Info"

5.  Handling of a verification error when there are multiple Identity
    header fields

   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 [RFC3326], 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 PASSporT identifier, "ppi", parameter
   containing the PASSporT string as an identifier for the identity
   header and corresponding PASSporT that generated the error to the
   Reason header field.  The "ppi" parameter for the Reason header field
   is optional, but RECOMMENDED, in particular for cases that a SIP
   INVITE contains multiple Identity header fields.  As implied and
   defined in [RFC8224], error codes associated with STIR targeted at
   authentication services that produced a specific identity header
   represent a single error occurring with the verification and
   processing of that identity header.  Therefore the association of a
   "ppi" parameter with a Reason header using "STIR" protocol MUST only
   identify a single cause code in the context of a call dialog defined
   in [RFC8224] or in future documents defining STIR related errors.
   The PASSporT can be included in full form or in compact form, where
   only the signature of the PASSporT is included with two periods as a
   prefix as defined in [RFC8225] Section 7 to identify the reported
   Identity header field with an error.  Compact form is the recommended
   form as full form may include information that could have privacy or
   security implications in some call scenarios as discussed in
   Section 9.

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   Example Reason header field with full form PASSporT:

   Reason: STIR ;cause=436 ;text="Bad Identity Info" ;ppi= \
   "eyJhbGciOiJFUzI1NiIsInR5cCI6InBhc3Nwb3J0IiwieDV1I \
   joiaHR0cHM6Ly9jZXJ0LmV4YW1wbGUub3JnL3Bhc3Nwb3J0LmNlciJ9.eyJ \
   kZXN0Ijp7InVyaSI6WyJzaXA6YWxpY2VAZXhhbXBsZS5jb20iXX0sImlhdC \
   I6IjE0NDMyMDgzNDUiLCJvcmlnIjp7InRuIjoiMTIxNTU1NTEyMTIifX0.r \
   q3pjT1hoRwakEGjHCnWSwUnshd0-zJ6F1VOgFWSjHBr8Qjpjlk-cpFYpFYs \
   ojNCpTzO3QfPOlckGaS6hEck7w"

   Example Reason header field with compact form PASSporT:

   Reason: STIR ;cause=436 ;text="Bad Identity Info" ;ppi= \
   "..rq3pjT1akEGjHCnWSwUnshd0-zJ6F1VOgFWSjHBr8Qjpjlk-cpFYpFYs \
   ojNCpTzO3QfPOlckGaS6hEck7w"

6.  Handling multiple verification errors

   If there are multiple Identity header field verification errors being
   reported the verification service SHOULD include a corresponding
   number of Reason header fields per error.  These Reason header fields
   should include a "ppi" parameters including the full or compact form
   of the PASSporT with cause and text parameters identifying each
   error.  As mentioned previously, the potential use of multiple Reason
   header fields defined in [RFC3326] is updated in
   [I-D.ietf-sipcore-multiple-reasons] allowing multiple Reason header
   fields with the same protocol value, for this specification "STIR"
   should be used for any STIR error defined in [RFC8224] or future
   specifications.

   Example Reason header fields for two identity info errors:

   Reason: STIR ;cause=436 ;text="Bad Identity Info" ;ppi=     \
   "..rq3pjT1hoRwakEGjHCnWSwUnshd0-zJ6F1VOgFWSjHBr8Qjpjlk-cpFY \
   pFYsojNCpTzO3QfPOlckGaS6hEck7w"

   Reason: STIR ;cause=438 ; text="Invalid Identity Header" ;ppi=  \
   "..rJ6F1VOgFWSjHBr8Qjpjlk-cpFYpFYsq3pjT1hoRwakEGjHCnWSwUnsh \
   d0-zckGaS6hEck7wojNCpTzO3QfPOl"

7.  Removal of the Reason header field by Authentication Service

   When an Authentication Service [RFC8224] 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

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   from going upstream to a UAC or UAS that may not be authorized to see
   claim information contained in the PASSporT for privacy or other
   reasons.

8.  IANA Considerations

   This document requests the definition of a new protocol value (and
   associated protocol cause) to be registered by the IANA into the
   "Reason Protocols" sub-registry under
   http://www.iana.org/assignments/sip-parameters as follows:

   Protocol Value   Protocol Cause            Reference
   --------------   ---------------           -----------
   STIR             STIR Error code           RFC 8224

   This document also requests the definition of a new header field
   parameter name to be registered by IANA into the Header Field
   Parameters and Parameter Values sub-registry under
   https://www.iana.org/assignments/sip-parameters as follows:

   Header Field   Parameter Name   Predefined Values  Reference
   ------------   --------------   -----------------  ---------
   Reason         ppi               No                RFC THIS

9.  Security Considerations

   This specification discusses the use of a PASSporT as an identifier
   for cases where there are multiple identity header errors occuring as
   part of the Reason header field response.  For some call scenarios
   (e.g. diversion based call flows) the signer of the PASSporT(s) may
   not be the first hop initiator of the call.  In those cases, there
   may be some security or privacy concerns associated with PASSporT
   information that is passed upstream beyond the authentication service
   that originally signed the PASSporT(s) in the resulting error Reason
   header field.  This specification states the authentication service
   MUST remove the Reason header field with the PASSporT to protect the
   security (e.g. use of potentially still fresh PASSporT for replay
   attacks) and privacy of any potential information that could be
   passed beyond the authentication service response back in the
   direction of the call initiator.  While this specification allows for
   both full and compact form of the PASSporT to be used as the error
   identifier, use of the compact form is RECOMMENDED to avoid the
   potential exposure of call information contained in the full form of
   the PASSporT.

10.  References

10.1.  Normative References

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   [I-D.ietf-sipcore-multiple-reasons]
              Sparks, R., "Multiple SIP Reason Header Field Values",
              Work in Progress, Internet-Draft, draft-ietf-sipcore-
              multiple-reasons-01, 23 August 2022,
              <https://www.ietf.org/archive/id/draft-ietf-sipcore-
              multiple-reasons-01.txt>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC3326]  Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason
              Header Field for the Session Initiation Protocol (SIP)",
              RFC 3326, DOI 10.17487/RFC3326, December 2002,
              <https://www.rfc-editor.org/info/rfc3326>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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,
              <https://www.rfc-editor.org/info/rfc8224>.

   [RFC8225]  Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
              Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
              <https://www.rfc-editor.org/info/rfc8225>.

   [RFC8226]  Peterson, J. and S. Turner, "Secure Telephone Identity
              Credentials: Certificates", RFC 8226,
              DOI 10.17487/RFC8226, February 2018,
              <https://www.rfc-editor.org/info/rfc8226>.

10.2.  Informative References

   [RFC7340]  Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
              Telephone Identity Problem Statement and Requirements",
              RFC 7340, DOI 10.17487/RFC7340, September 2014,
              <https://www.rfc-editor.org/info/rfc7340>.

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Appendix A.  Acknowledgements

   The author would like to thank David Hancock for help to identify
   these error scenarios and additionally Jon Peterson, Roman Shpount,
   Robert Sparks, Christer Holmberg and others in the STIR working group
   for their helpful feedback and discussion.

Author's Address

   Chris Wendt
   Somos Inc.
   Email: chris-ietf@chriswendt.net

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