The Session Initiation Protocol (SIP) Digest Access Authentication Scheme
RFC 8760

Document Type RFC - Proposed Standard (March 2020; No errata)
Updates RFC 3261
Author Rifaat Shekh-Yusef 
Last updated 2020-03-19
Replaces draft-yusef-sipcore-digest-scheme
Stream IETF
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Stream WG state Submitted to IESG for Publication
Document shepherd Jean Mahoney
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IESG IESG state RFC 8760 (Proposed Standard)
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Internet Engineering Task Force (IETF)                    R. Shekh-Yusef
Request for Comments: 8760                                         Avaya
Updates: 3261                                                 March 2020
Category: Standards Track                                               
ISSN: 2070-1721

   The Session Initiation Protocol (SIP) Digest Access Authentication


   This document updates RFC 3261 by modifying the Digest Access
   Authentication scheme used by the Session Initiation Protocol (SIP)
   to add support for more secure digest algorithms, e.g., SHA-256 and
   SHA-512/256, to replace the obsolete MD5 algorithm.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   than English.

Table of Contents

   1.  Introduction
     1.1.  Terminology
   2.  Updates to the SIP Digest Access Authentication Scheme
     2.1.  Hash Algorithms
     2.2.  Representation of Digest Values
     2.3.  UAS Behavior
     2.4.  UAC Behavior
     2.5.  Forking
     2.6.  HTTP Digest Authentication Scheme Modifications
     2.7.  ABNF for SIP
   3.  Security Considerations
   4.  IANA Considerations
   5.  References
     5.1.  Normative References
     5.2.  Informative References
   Author's Address

1.  Introduction

   The Session Initiation Protocol [RFC3261] uses the same mechanism as
   the Hypertext Transfer Protocol (HTTP) does for authenticating users.
   This mechanism is called "Digest Access Authentication".  It is a
   simple challenge-response mechanism that allows a server to challenge
   a client request and allows a client to provide authentication
   information in response to that challenge.  The version of Digest
   Access Authentication that [RFC3261] references is specified in

   The default hash algorithm for Digest Access Authentication is MD5.
   However, it has been demonstrated that the MD5 algorithm is not
   collision resistant and is now considered a bad choice for a hash
   function (see [RFC6151]).

   The HTTP Digest Access Authentication document [RFC7616] obsoletes
   [RFC2617] and adds stronger algorithms that can be used with the
   Digest Access Authentication scheme and establishes a registry for
   these algorithms, known as the "Hash Algorithms for HTTP Digest
   Authentication" IANA registry, so that algorithms can be added in the

   This document updates the Digest Access Authentication scheme used by
   SIP to support the algorithms listed in the "Hash Algorithms for HTTP
   Digest Authentication" IANA registry defined by [RFC7616].

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

2.  Updates to the SIP Digest Access Authentication Scheme

   This section describes the modifications to the operation of the
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