draft-ietf-tls-ssl2-must-not-03.txt   draft-ietf-tls-ssl2-must-not-04.txt 
Network Working Group S. Turner Network Working Group S. Turner
Internet Draft IECA Internet Draft IECA
Updates: 5246, 4346, 2246 (once approved) T. Polk Updates: 5246, 4346, 2246 (once approved) T. Polk
Intended Status: Standards Track NIST Intended Status: Standards Track NIST
Expires: May 29, 2011 November 29, 2010 Expires: June 16, 2011 December 16, 2010
Prohibiting SSL Version 2.0 Prohibiting SSL Version 2.0
draft-ietf-tls-ssl2-must-not-03.txt draft-ietf-tls-ssl2-must-not-04.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). sections found in the Transport Security Layer (TLS).
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 May 29, 2009. This Internet-Draft will expire on May 16, 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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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) [TLS1.0][TLS1.1][TLS1.2] for security services. This is a good (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 thing, but some TLS clients and servers also support negotiating the
use of Secure Sockets Layer (SSL) version 2.0 [SSL2]; however, this use of Secure Sockets Layer (SSL) version 2.0 [SSL2]; however, this
version does not provide the expected level of security. SSL version version does not provide a sufficiently high level of security. SSL
2.0 has known deficiencies. This document describes those version 2.0 has known deficiencies. This document describes those
deficiencies, and it requires TLS clients and servers never negotiate deficiencies, and it requires TLS clients and servers never negotiate
the use of SSL version 2.0. the use of SSL version 2.0.
This document updates the backward compatibility sections found in TLS 1.1 [RFC4346] and later in TLS 1.2 [RFC5246] explicitly warned
TLS [TLS1.0][TLS1.1][TLS1.2]. implementers that the "ability to send version 2.0 CLIENT-HELLO
messages will be phased out with all due haste." This document
accomplishes this by updating the backward compatibility sections
found in TLS [TLS1.0][TLS1.1][TLS1.2].
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
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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 send the SSL version 2.0 compatible CLIENT-
HELLO message format. Clients MUST NOT send any client hello
message which specifies a protocol version less than
{ 0x03, 0x00 }. As previously stated by the definitions of all
previous versions of TLS, the client SHOULD specify the highest
protocol version it supports.
o TLS clients MUST NOT send SSL 2.0 CLIENT-HELLO messages. o TLS servers MAY continue to accept CLIENT-HELLO messages in the
version 2 CLIENT-HELLO format as specified in TLS 1.2 [RFC5246]
Appendix E.2. Note that this does not contradict the prohibition
against actually negotiating the use of SSL 2.0.
o TLS servers MUST NOT negotiate or use SSL 2.0. TLS Servers MUST NOT reply with a SSL 2.0 SERVER-HELLO with a
protocol version which is less than { 0x03, 0x00 } and instead
MUST abort the connection, i.e., when the highest protocol version
offered by the client is { 0x02, 0x00 } the TLS connection will be
refused.
As described in TLSv1.2 ([TLS1.2] Appendix E.2), TLS servers that do Note that the number of servers that support this above-mentioned
not support SSL 2.0 MAY accept version 2.0 CLIENT-HELLO messages as "MAY accept" implementation option is declining, and the SSL 2.0
the first message of a TLS handshake for interoperability with old CLIENT-HELLO precludes the use of TLS protocol enhancements that
clients. require TLS extensions. TLS extensions can only be sent as part of an
(Extended) ClientHello handshake message.
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
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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, Tom Petch, Yngve Pettersen, Marsh Ray, Martin Rex, Mavrogiannopoulos, Tom Petch, Yngve Pettersen, Marsh Ray, Martin Rex,
and Yaron Sheffer for their reviews and comments. Yaron Sheffer, and Glen Zorn 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.
[TLS1.0] Dierks, T., and C. Allen, "The TLS Protocol Version [TLS1.0] Dierks, T., and C. Allen, "The TLS Protocol Version
1.0", RFC 2246, January 1999. 1.0", RFC 2246, January 1999.
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