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Versions: (draft-turner-ssl-must-not) 00 01
02 03 04 RFC 6176
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
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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.
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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
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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.
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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.
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[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
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