draft-ietf-tls-ssl2-must-not-00.txt   draft-ietf-tls-ssl2-must-not-01.txt 
Network Working Group S. Turner Network Working Group S. Turner
Internet Draft IECA Internet Draft IECA
Updates: 5246 (once approved) Tim Polk Updates: 5246 (once approved) Tim Polk
Intended Status: Standards Track NIST Intended Status: Standards Track NIST
Expires: February 23, 2011 August 23, 2010 Expires: April 7, 2011 October 7, 2010
Prohibiting SSL Version 2.0 Prohibiting SSL Version 2.0
draft-ietf-tls-ssl2-must-not-00.txt draft-ietf-tls-ssl2-must-not-01.txt
Abstract Abstract
This document requires that when TLS clients and servers establish This document requires that when TLS clients and servers establish
connections that they never negotiate the use of Secure Sockets Layer connections that they never negotiate the use of Secure Sockets Layer
(SSL) version 2.0. This document updates the backward compatibility (SSL) version 2.0. This document updates the backward compatibility
sections found in the Transport Security Layer (TLS) Protocol, RFC sections found in the Transport Security Layer (TLS) Protocol, RFC
5246. 5246.
Status of this Memo Status of this Memo
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on February 23, 2009. This Internet-Draft will expire on April 7, 2009.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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the Transport Security Layer (TLS) Protocol [TLS] and earlier the Transport Security Layer (TLS) Protocol [TLS] and earlier
versions. versions.
1.1. Requirements Terminology 1.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
2. SSL 2.0 2. SSL 2.0 Deficiencies
SSL version 2.0 [SSL2] deficiencies include: SSL version 2.0 [SSL2] deficiencies include:
o Message authentication uses MD5 [MD5]. Most security-aware users o Message authentication uses MD5 [MD5]. Most security-aware users
have already moved away from any of MD5 have already moved away from any use of MD5
[I-D.turner-md5-seccon-update]. [I-D.turner-md5-seccon-update].
o Handshake messages are not protected. This permits a man-in-the- o Handshake messages are not protected. This permits a man-in-the-
middle to trick the client into picking a weaker cipher suite than middle to trick the client into picking a weaker cipher suite than
they would normally choose. they would normally choose.
o Message integrity and message encryption use the same key, which o Message integrity and message encryption use the same key, which
is a problem if the client and server negotiate a weak encryption is a problem if the client and server negotiate a weak encryption
algorithm. algorithm.
o Sessions can be easily terminated. A man-in-the-middle can easily 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 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. determine whether or not it was a legitimate end of the session.
3. Changes to TLS 3. Changes to TLS
Because of the deficiencies noted in the previous sections, TLS Because of the deficiencies noted in the previous section:
implementations MUST NOT support SSL 2.0. The specific changes to
[TLS], including earlier versions, are as follows:
o TLS clients MUST NOT use SSL 2.0 ClientHello messages. o TLS clients MUST NOT negotiate or use SSL 2.0.
o TLS servers MUST NOT accept SSL 2.0 ClientHello messages. o TLS clients MUST NOT send SSL 2.0 ClientHello messages.
o TLS servers MUST NOT negotiate or use SSL 2.0.
As described in [TLS], 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 4. IANA Considerations
None. None.
5. Security Considerations 5. Security Considerations
This entire document is about security considerations. This entire document is about security considerations.
6. Acknowledgements 6. Acknowledgements
The idea for this document was inspired by discussions between Peter The idea for this document was inspired by discussions between Peter
Saint Andre, Simon Josefsson, and others on the XMPP mailing list. Saint Andre, Simon Josefsson, and others on the XMPP mailing list.
We would also like to thank Paul Hoffman, Yaron Sheffer, and Nikos We would also like to thank Michael D'Errico, Paul Hoffman, Nikos
Mavrogiannopoulos, Yngve Pettersen, Marsh Ray, and Martin Rex for Mavrogiannopoulos, Yngve Pettersen, Marsh Ray, Martin Rex, and Yaron
reviews and comments on earlier versions of this document. Sheffer for their reviews and comments.
7. References 7. References
7.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[TLS] Dierks, T. and E. Rescorla, "The Transport Layer [TLS] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246, Security (TLS) Protocol Version 1.2", RFC 5246,
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