draft-ietf-tls-ssl2-must-not-02.txt   draft-ietf-tls-ssl2-must-not-03.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, 4346, 2246 (once approved) T. Polk
Intended Status: Standards Track NIST Intended Status: Standards Track NIST
Expires: April 8, 2011 October 8, 2010 Expires: May 29, 2011 November 29, 2010
Prohibiting SSL Version 2.0 Prohibiting SSL Version 2.0
draft-ietf-tls-ssl2-must-not-02.txt draft-ietf-tls-ssl2-must-not-03.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).
5246.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. This document may contain material provisions of BCP 78 and BCP 79. This document may contain material
from IETF Documents or IETF Contributions published or made publicly from IETF Documents or IETF Contributions published or made publicly
available before November 10, 2008. available before November 10, 2008.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
skipping to change at page 1, line 42 skipping to change at page 1, line 41
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
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This Internet-Draft will expire on April 8, 2009. This Internet-Draft will expire on May 29, 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
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publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
1. Introduction 1. Introduction
Many protocols specified in the IETF rely on Transport Layer Security Many protocols specified in the IETF rely on Transport Layer Security
(TLS) [TLS] for security services. This is a good thing, but some (TLS) [TLS1.0][TLS1.1][TLS1.2] for security services. This is a good
TLS clients and servers also support negotiating the use of SSL thing, but some TLS clients and servers also support negotiating the
version 2.0 [SSL2]; however, this version does not provide the use of Secure Sockets Layer (SSL) version 2.0 [SSL2]; however, this
expected level of security. SSL version 2.0 has known deficiencies. version does not provide the expected level of security. SSL version
This document describes those deficiencies, and it requires TLS 2.0 has known deficiencies. This document describes those
clients and servers never negotiate the use of SSL version 2.0. 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 This document updates the backward compatibility sections found in
the Transport Security Layer (TLS) Protocol [TLS] and earlier TLS [TLS1.0][TLS1.1][TLS1.2].
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 Deficiencies 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 use 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
is a problem if the client and server negotiate a weak encryption 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 section: 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 negotiate or use SSL 2.0.
o TLS clients MUST NOT send SSL 2.0 CLIENT-HELLO messages. o TLS clients MUST NOT send SSL 2.0 CLIENT-HELLO messages.
o TLS servers MUST NOT negotiate or use SSL 2.0. 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 As described in TLSv1.2 ([TLS1.2] Appendix E.2), TLS servers that do
accept version 2.0 CLIENT-HELLO messages as the first message of a not support SSL 2.0 MAY accept version 2.0 CLIENT-HELLO messages as
TLS handshake for interoperability with old clients. 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 Michael D'Errico, Paul Hoffman, Nikos We would also like to thank Michael D'Errico, Paul Hoffman, Nikos
Mavrogiannopoulos, Yngve Pettersen, Marsh Ray, Martin Rex, and Yaron Mavrogiannopoulos, Tom Petch, Yngve Pettersen, Marsh Ray, Martin Rex,
Sheffer for their reviews and comments. and Yaron 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 [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.
[TLS1.2] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246, Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008. August 2008.
7.2. Informative References 7.2. Informative References
[MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC
1321, April 1992. 1321, April 1992.
[SSL2] Hickman, Kipp, "The SSL Protocol", Netscape [SSL2] Hickman, Kipp, "The SSL Protocol", Netscape
Communications Corp., Feb 9, 1995. Communications Corp., Feb 9, 1995.
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