SIPCORE Working Group R. Shekh-Yusef INTERNET-DRAFT Avaya Intended Status: Standards Track January 10, 2014 Expires: July 14, 2014 The Session Initiation Protocol (SIP) Digest Authentication Scheme draft-yusef-sipcore-digest-scheme-00 Abstract This document updates the Digest Access Authentication scheme used by the Session Initiation Protocol (SIP) to add support for SHA2 digest algorithms to replace the MD5 algorithm. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright and License Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Shekh-Yusef Expires July 14, 2014 [Page 1]
INTERNET DRAFT SIP Digest Authentication Scheme January 10, 2014 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 2 The SIP Digest Authentication Scheme . . . . . . . . . . . . . 3 3 Augmented BNF for the SIP Protocol . . . . . . . . . . . . . . 6 4 Security Considerations . . . . . . . . . . . . . . . . . . . . 6 5 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6 7 References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7.1 Normative References . . . . . . . . . . . . . . . . . . . 7 7.2 Informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Shekh-Yusef Expires July 14, 2014 [Page 2]
INTERNET DRAFT SIP Digest Authentication Scheme January 10, 2014 1 Introduction The SIP protocol [RFC3261] uses the same mechanism used by the HTTP protocol for authenticating users, which is a simple challenge- response authentication mechanism that allows a server to challenge a client request and allows a client to provide authentication information in response to that challenge. The SIP protocol uses the Digest Authentication scheme that is used with the HTTP authentication mechanism, which by default uses MD5 as the default algorithm. The HTTP Digest Access Authentication [HTTP-DIGEST] document defines the challenge-response authentication mechanism and the Digest Authentication scheme, and defines few algorithms that could be used with the Digest Authentication scheme, and establishes a registry for these algorithms to allow for additional algorithms to be added in the future. In 2008 the US-CERT issued a note that MD5 "should be considered cryptographically broken and unsuitable for further use" [CERT-VU]. This document updates the Digest Access Authentication scheme used by SIP to add support for SHA2 digest algorithms to replace the MD5 algorithm. This document replaces what is specified in RFC3261, Section 22.4. 1.1 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 RFC 2119 [RFC2119]. 2 The SIP Digest Authentication Scheme This document describes the modifications and clarifications required to apply the HTTP Digest Authentication scheme to SIP. The SIP scheme usage is almost completely identical to that for HTTP [HTTP-DIGEST]. Since RFC 2543 is based on HTTP Digest as defined in RFC 2069, SIP servers supporting [HTTP-DIGEST] MUST ensure they are backwards compatible with RFC 2069. Procedures for this backwards compatibility are specified in [HTTP-DIGEST]. Note, however, that SIP servers MUST NOT accept or request Basic authentication. Shekh-Yusef Expires July 14, 2014 [Page 3]
INTERNET DRAFT SIP Digest Authentication Scheme January 10, 2014 The rules for Digest authentication follow those defined in [HTTP- DIGEST], with "HTTP/1.1" replaced by "SIP/2.0" in addition to the following differences: 1. The URI included in the challenge has the following BNF: URI = SIP-URI / SIPS-URI 2. The BNF for digest-uri-value is: digest-uri-value = Request-URI 3. The example procedure for choosing a nonce based on Etag does not work for SIP. 4. The text in [HTTP-DIGEST] regarding cache operation does not apply to SIP. 5. [HTTP-DIGEST] requires that a server check that the URI in the request line and the URI included in the Authorization header field point to the same resource. In a SIP context, these two URIs may refer to different users, due to forwarding at some proxy. Therefore, in SIP, a server MAY check that the Request-URI in the Authorization header field value corresponds to a user for whom the server is willing to accept forwarded or direct requests, but it is not necessarily a failure if the two fields are not equivalent. 6. As a clarification to the calculation of the A2 value for message integrity assurance in the Digest authentication scheme, implementers should assume, when the entity-body is empty (that is, when SIP messages have no body) that the hash of the entity-body resolves to the hash of an empty string as follows: H(entity-body) = MD5("") = "d41d8cd98f00b204e9800998ecf8427e" H(entity-body) = SHA2-256("") = "TODO" H(entity-body) = SHA2-512-256("") = Shekh-Yusef Expires July 14, 2014 [Page 4]
INTERNET DRAFT SIP Digest Authentication Scheme January 10, 2014 "TODO" 7. [HTTP-DIGEST] notes that a cnonce value MUST NOT be sent in an Authorization (and by extension Proxy-Authorization) header field if no qop directive has been sent. Therefore, any algorithms that have a dependency on the cnonce (including "MD5-sess", "SHA2-256-sess", and "SHA2-512-256-sess") require that the qop directive be sent. Use of the "qop" parameter is optional in [HTTP-DIGEST] for the purposes of backwards compatibility with RFC 2069; since RFC 2543 was based on RFC 2069, the "qop" parameter must unfortunately remain optional for clients and servers to receive. However, servers MUST always send a "qop" parameter in WWW-Authenticate and Proxy-Authenticate header field values. If a client receives a "qop" parameter in a challenge header field, it MUST send the "qop" parameter in any resulting authorization header field. RFC 2543 did not allow usage of the Authentication-Info header field (it effectively used RFC 2069). However, we now allow usage of this header field, since it provides integrity checks over the bodies and provides mutual authentication. [HTTP-DIGEST] defines mechanisms for backwards compatibility using the qop attribute in the request. These mechanisms MUST be used by a server to determine if the client supports the new mechanisms in [HTTP-DIGEST] that were not specified in RFC 2069. [OPEN ISSUE:] Should the backward compatibility with RFC2543/RFC2069 be deprecated? Shekh-Yusef Expires July 14, 2014 [Page 5]
INTERNET DRAFT SIP Digest Authentication Scheme January 10, 2014 3 Augmented BNF for the SIP Protocol This document updates the Augmented BNF for the SIP Protocol as follows. It extends the request-digest as follows to allow for different digest sizes: request-digest = LDQUOT digest-size LHEX RDQUOT digest-size = "32" / "64" It extends the algorithm parameter as follows to allow for SHA2 algorithms to be used: algorithm = "algorithm" EQUAL ( "MD5" / "MD5-sess" / "SHA2-256" / "SHA2-256-sess" / "SHA2-512-256" / "SHA2-512-256-sess" / token ) 4 Security Considerations <Security considerations text> 5 IANA Considerations The [HTTP-DIGEST] defines an IANA registry named "HTTP Digest Hash Algorithms" to simplify the introduction of new algorithms in the future. This document will use the algorithms defined in that registry. 6 Acknowledgments <Acknowledgments text> Shekh-Yusef Expires July 14, 2014 [Page 6]
INTERNET DRAFT SIP Digest Authentication Scheme January 10, 2014 7 References 7.1 Normative References [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 7.2 Informative References Authors' Addresses Rifaat Shekh-Yusef Avaya 250 Sydney Street Belleville, Ontario Canada Phone: +1-613-967-5267 Email: rifaat.ietf@gmail.com Shekh-Yusef Expires July 14, 2014 [Page 7]