Network Working Group S. Turner Internet Draft IECA Updates: 5246, 4346, 2246 (once approved) T. Polk Intended Status: Standards Track NIST Expires: May 29, 2011 November 29, 2010 Prohibiting SSL Version 2.0 draft-ietf-tls-ssl2-must-not-03.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 2.0. This document updates the backward compatibility sections found in the Transport Security Layer (TLS). 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 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/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 29, 2009. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. Turner & Polk Expires May 29, 2011 [Page 1]
Internet-Draft Prohibiting SSL 2.0 November 2010 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 Secure Sockets Layer (SSL) version 2.0 [SSL2]; however, this version does not provide the expected level of security. SSL version 2.0 has known deficiencies. This document describes those deficiencies, and it requires TLS clients and servers never negotiate the use of SSL version 2.0. This document updates the backward compatibility sections found in TLS [TLS1.0][TLS1.1][TLS1.2]. 1.1. Requirements Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. SSL 2.0 Deficiencies SSL version 2.0 [SSL2] deficiencies include: o Message authentication uses MD5 [MD5]. Most security-aware users have already moved away from any use of MD5 [I-D.turner-md5-seccon-update]. 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. Turner and Polk Expires May 29, 2011 [Page 2]
Internet-Draft Prohibiting SSL 2.0 November 2010 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. Changes to TLS Because of the deficiencies noted in the previous section: o TLS clients MUST NOT negotiate or use SSL 2.0. o TLS clients MUST NOT send SSL 2.0 CLIENT-HELLO messages. o TLS servers MUST NOT negotiate or use SSL 2.0. As described in TLSv1.2 ([TLS1.2] Appendix E.2), TLS servers that do not support SSL 2.0 MAY accept version 2.0 CLIENT-HELLO messages as the first message of a TLS handshake for interoperability with old clients. 4. IANA Considerations None. 5. Security Considerations This entire document is about security considerations. 6. Acknowledgements The idea for this document was inspired by discussions between Peter Saint Andre, Simon Josefsson, and others on the XMPP mailing list. We would also like to thank Michael D'Errico, Paul Hoffman, Nikos Mavrogiannopoulos, Tom Petch, Yngve Pettersen, Marsh Ray, Martin Rex, and Yaron Sheffer for their reviews and comments. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [TLS1.0] Dierks, T., and C. Allen, "The 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 4346, April 2006. Turner and Polk Expires May 29, 2011 [Page 3]
Internet-Draft Prohibiting SSL 2.0 November 2010 [TLS1.2] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. 7.2. Informative References [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. [SSL2] Hickman, Kipp, "The SSL Protocol", Netscape Communications Corp., Feb 9, 1995. [I-D.turner-md5-seccon-update] Turner, S., and L. Chen, "Updated Security Considerations for the MD5 Message-Digest Algorithm", draft-turner-md5-seccon-update, work-in- progress. 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 Turner and Polk Expires May 29, 2011 [Page 4]
