The Session Initiation Protocol (SIP) Digest Authentication Scheme
draft-yusef-sipcore-digest-scheme-01

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.

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   Copyright (c) 2014 IETF Trust and the persons identified as the
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   (http://trustee.ietf.org/license-info) in effect on the date of
 

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   publication of this document. Please review these documents
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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

 

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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].

 

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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-
 

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   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. 
 

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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

   <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>

 

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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

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