SIPCORE Working Group R. Shekh-Yusef INTERNET-DRAFT Avaya Updates: 3261 (if approved) January 16, 2014 Intended Status: Standards Track Expires: July 20, 2014 The Session Initiation Protocol (SIP) Digest Authentication Scheme draft-yusef-sipcore-digest-scheme-01 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. 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Table of Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 2 The SIP Digest Authentication Scheme . . . . . . . . . . . . . 4 2.1 Hash Algorithms . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Representation of Digest Values . . . . . . . . . . . . . . 4 2.3 The Authenticate Response Header . . . . . . . . . . . . . 4 2.4 The Authorization Request Header . . . . . . . . . . . . . 5 2.5 HTTP Modifications . . . . . . . . . . . . . . . . . . . . 5 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 20, 2014 [Page 2] INTERNET DRAFT SIP Digest Authentication Scheme January 16, 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. 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]. Shekh-Yusef Expires July 20, 2014 [Page 3] INTERNET DRAFT SIP Digest Authentication Scheme January 16, 2014 2 The SIP Digest Authentication Scheme This section describes the modifications to the operation of the Digest mechanism as specified in RFC3261. 2.1 Hash Algorithms The Digest scheme has an 'algorithm' parameter that specifies the algorithm to be used to compute the digest of the response. RFC3261 specifies only one algorithm, MD5, which is used by default. This document adds two new algorithms, to align with the [HTTP- DIGEST], that SHOULD be used instead of MD5: SHA2-256 & SHA2-512/256. This document defines the following preference list, starting with the most preferred algorithm: * SHA2-256 (most preferred) * SHA2-512/256 * MD5 (least preferred) 2.2 Representation of Digest Values The size of the digest depends on the algorithm used. The bits in the digest are converted from the most significant to the least significant bit, four bits at a time to the ASCII representation as follows. Each four bits is represented by its familiar hexadecimal notation from the characters 0123456789abcdef, that is binary 0000 is represented by the character '0', 0001 by '1' and so on up to the representation of 1111 as 'f'. If the MD5 algorithm is used to calculate the digest, then the digest will be represented as 32 hexadecimal characters, SHA2-256 and SHA2-512/256 by 64 hexadecimal characters. 2.3 The Authenticate Response Header When a UAS receives a request from a UAC, and an acceptable Authorization header is not sent, the UAS can challenge the originator to provide credentials by rejecting the request with a 401/407 status code with the WWW-Authenticate/Proxy-Authenticate header field. The UAS MAY include multiple WWW-Authenticate/Proxy- Authenticate headers to allow the UAS to utilize the best available algorithm supported by the client. If the UAS challenges with multiple WWW-Authenticate/Proxy- Shekh-Yusef Expires July 20, 2014 [Page 4] INTERNET DRAFT SIP Digest Authentication Scheme January 16, 2014 Authenticate headers, then each one of these headers MUST use a different digest algorithm. The UAS MUST add these headers to the response in order of preference, starting with the most preferred header, followed by the less preferred headers. 2.4 The Authorization Request Header When the UAC receives the response it SHOULD use the topmost header that it supports, unless a local policy dictates otherwise. The client should ignore any challenge it does not understand. 2.5 HTTP Modifications RFC3261 Section 22.4, describes the modifications and clarifications required to apply the HTTP Digest Authentication scheme to SIP. This section describes the modifications to section 22.4 to take into considerations the changes introduced in the previous sections. The following is the list of bullets that require some changes: * Bullet 2: The error mentioned in this bullet has been fixed in [HTTP-DIGEST]. * Bullet 7: H(entity-body) = SHA2-256("") = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855" H(entity-body) = SHA2-512-256("") = "c672b8d1ef56ed28ab87c3622c5114069bdd3ad7b8f9737498d0c01ecef0967a" * Bullet 8: This bullet discusses cnonce dependency and backward compatibility issues. [OPEN ISSUE:] Should the backward compatibility with RFC2543/RFC2069 be deprecated? which means that we would make the qop parameter mandatory and require the client and server to take it into considerations when received. Shekh-Yusef Expires July 20, 2014 [Page 5] INTERNET DRAFT SIP Digest Authentication Scheme January 16, 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 32LHEX RDQUOT / LDQUOT 64LHEX RDQUOT 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 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 Shekh-Yusef Expires July 20, 2014 [Page 6] INTERNET DRAFT SIP Digest Authentication Scheme January 16, 2014 7 References 7.1 Normative References [HTTP-DIGEST] Shekh-Yusef, R., Ahrens, D., and Bremer, S., "HTTP Digest Access Authentication", Work in Progress, January 2014. https://datatracker.ietf.org/doc/draft-ietf-httpauth-digest/ 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 20, 2014 [Page 7]