One document matched: draft-turner-ssl-must-not-00.txt

Network Working Group                                         S. Turner 
Internet Draft                                                     IECA 
Updates: 5246 (once approved)                                  Tim Polk 
Intended Status: BCP                                               NIST 
Expires: December 22, 2010                                June 22, 2010 
 
 
                                      
                  Prohibiting SSL Version 3.0 and Earlier 
                     draft-turner-ssl-must-not-00.txt 

Abstract 

   This document requires that when TLS clients and servers establish 
   connections that they never negotiate the use of Secure Sockets Layer 
   (SSL) version 3.0 or earlier.  In addition, this document recommends 
   that TLS clients and servers not use TLS 1.0/SSL 3.1.  This document 
   updates the backward compatibility sections found in the Transport 
   Security Layer (TLS) Protocol, RFC 5246. 

Status of this Memo 

   This Internet-Draft is submitted in full conformance with the 
   provisions of BCP 78 and BCP 79.  This document may contain material 
   from IETF Documents or IETF Contributions published or made publicly 
   available before November 10, 2008. 

   Internet-Drafts are working documents of the Internet Engineering 
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   This Internet-Draft will expire on December 22, 2010. 




 
 
 
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Copyright Notice 

   Copyright (c) 2010 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 
   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. 

1. Introduction 

   Many protocols specified in the IETF rely on Transport Layer Security 
   (TLS) [TLS1.0][TLS1.1][TLS1.2] for security services.  This is a good 
   thing, but some TLS clients and servers also support negotiating the 
   use of SSL version 2.0 [SSL2] and/or 3.0 [SSL3]; however, these 
   versions will not provide the expected level of security.  Both SSL 
   version 2.0 and 3.0 have known deficiencies. This document describes 
   those deficiencies, and it requires TLS clients and servers never 
   negotiate the use of SSL version 2.0 or 3.0. 

   TLS has evolved from TLS 1.0 through 1.2.  One change, which is 
   addressed in Section 4, adopted by TLS 1.1 mitigates an attack 
   against CBC modes used by TLS 1.0.  As a result of this concern with 
   TLS 1.0 this document recommends that TLS clients and servers never 
   negotiate the use of TLS 1.0.  Note that TLS 1.0 and SSL 3.1 are 
   equivalent. 

   This document updates the backward compatibility sections found in 
   the Transport Security Layer (TLS) Protocol, RFC 5246. 

1.1. Requirements 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 [WORDS]. 

2. SSL2 Deficiencies 

   SSL version 2.0 [SSL2] deficiencies include: 

   o Message authentication uses MD5 [MD5].  MD5 is universally accepted 
     as a broken hash algorithm. 
 
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   o Handshake messages are not protected.  This permits a man-in-the-
     middle to trick the client into picking a weaker cipher suite than 
     they would normally choose. 

   o Message integrity and message encryption use the same key, which is 
     a problem if the client and server negotiate a weak encryption 
     algorithm. 

   o Sessions can be easily terminated.  A man-in-the-middle can easily 
     insert a TCP FIN to close the session and the peer is unable to 
     determine whether or not it was a legitimate end of the session. 

3. SSL3 Deficiencies 

   SSL version 3.0 [SSL3] has a primary key derivation function (KDF) 
   deficiency.  The SSL 3.0 KDF, which is used by all SSL 3.0 cipher 
   suites, depends entirely upon the MD5 hash function [MD5] for half of 
   the master key set up during the SSL key exchange.  MD5 is not 
   collision resistant and the pre-image resistance has been weakened by 
   recent attacks. 

4. TLS 1.0 Deficiencies 

   TLS 1.0 [TLS1.0] is an improvement over SSL 2.0 and 3.0; however, it 
   too has deficiencies: 

   o TLS 1.0 did not have explicit initialization vectors (IVs) in CBC 
     mode.  Explicit IVs were added to TLS 1.1 to prevent the attacks 
     described in [CBC-Issues]. 

   o Some TLS 1.0 implementations incorrectly fail the handshake when 
     there is data (e.g., extensions) following the ClientHello that 
     they do not understand.  This was a problem addressed in 
     [RFC5746]. 

5. Use TLS 1.1 and Later Versions 

   Because of the deficiencies noted in the previous sections, TLS 
   implementations MUST NOT support SSL 3.0 or earlier. Support for TLS 
   1.2 is RECOMMENDED.  To ensure interoperability, TLS implementations 
   MUST support TLS 1.0 and SHOULD support TLS 1.1 and 1.2.  That is, 
   TLS clients and servers MUST NOT request, offer, or use SSL 2.0 or 
   SSL 3.0 and SHOULD offer TLS 1.2.  The specific changes to {TLS1.2] 
   are as follows: 

   o TLS clients MUST NOT use SSL 2.0 ClientHello messages.  

   o TLS servers MUST NOT accept SSL 2.0 ClientHello messages.  
 
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   o TLS clients MUST NOT use {3,0} in ClientHello.client_version.  

   o TLS servers MUST NOT accept {3,0} in ClientHello.client_version; it 
     MUST send a "protocol_version" alert message and close the 
     connection. 

   o TLS clients SHOULD offer {3,3} in ClientHello.client_version. 

6. IANA Considerations 

   None. 

7. Security Considerations 

   The security considerations of [TLS1.0] [TLS1.1] [TLS1.2] apply; no 
   new security considerations are introduced by this document. 

   Since all recent TLS implementations support at least TLS 1.0/SSL 
   3.1, the risk of denial of service from the lack of interoperability 
   with earlier versions is considered minimal. 

8. Acknowledgements 

   The idea for this document was inspired by discussions between Peter 
   Saint Andre, Simon Josefsson, and others on the XMPP mailing list. 

9. References 

9.1. Normative References 

   [TLS1.0]         Dierks, T. and C. Allen, "The Transport Layer 
                    Security (TLS) Protocol Version 1.0", RFC 2246, 
                    January 1999. 

   [TLS1.1]         Dierks, T. and E. Rescorla, "The Transport Layer 
                    Security (TLS) Protocol Version 1.1", RFC 4246, 
                    April 2006. 

   [TLS1.2]         Dierks, T. and E. Rescorla, "The Transport Layer 
                    Security (TLS) Protocol Version 1.2", RFC 5246, 
                    August 2008. 

   [WORDS]          Bradner, S., "Key words for use in RFCs to Indicate 
                    Requirement Levels", BCP 14, RFC 2119, March 1997. 




 
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9.2. Informative References 

   [MD5]            Rivest, R., "The MD5 Message-Digest Algorithm", RFC 
                    1321, April 1992.  

   [RFC5746]        Rescorla, E., Ray, M., Dispensa, S., Oskov, N., 
                    "Transport Layer Security (TLS) Renegotiation 
                    Indication Extension", RFC 5746, February 2010. 

   [SSL2]           Hickman, Kipp, "The SSL Protocol", Netscape 
                    Communications Corp., Feb 9, 1995. 

   [SSL3]           A. Freier, P. Karlton, and P. Kocher, "The SSL 3.0 
                    Protocol", Netscape Communications Corp., Nov 18, 
                    1996. 

   [CBC-Issues]     Moeller, B., "Security of CBC Ciphersuites in 
                    SSL/TLS: Problems and Countermeasures", 
                    http://www.openssl.org/~bodo/tls-cbc.txt. 

Authors' Addresses 

   Sean Turner 
   IECA, Inc. 
   3057 Nutley Street, Suite 106 
   Fairfax, VA 22031 
   USA 

   EMail: turners@ieca.com 

   Tim Polk 
   National Institute of Standards and Technology 
   100 Bureau Drive, Mail Stop 8930 
   Gaithersburg, MD 20899-8930 
   USA 

   EMail: tim.polk@nist.gov  

    









 
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