Internet DRAFT - draft-ietf-tls-sslv3-diediedie
draft-ietf-tls-sslv3-diediedie
Network Working Group R. Barnes
Internet-Draft M. Thomson
Updates: 5246 (if approved) Mozilla
Intended status: Standards Track A. Pironti
Expires: October 12, 2015 INRIA
A. Langley
Google
April 10, 2015
Deprecating Secure Sockets Layer Version 3.0
draft-ietf-tls-sslv3-diediedie-03
Abstract
Secure Sockets Layer version 3.0 (SSLv3) [RFC6101] is not
sufficiently secure. This document requires that SSLv3 not be used.
The replacement versions, in particular Transport Layer Security
(TLS) 1.2 [RFC5246], are considerably more secure and capable
protocols.
This document updates the backward compatibility section of RFC 5246
and its predecessors to prohibit fallback to SSLv3.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 12, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Do Not Use SSL Version 3.0 . . . . . . . . . . . . . . . . . 3
4. SSLv3 is Comprehensively Broken . . . . . . . . . . . . . . . 3
4.1. Record Layer . . . . . . . . . . . . . . . . . . . . . . 3
4.2. Key Exchange . . . . . . . . . . . . . . . . . . . . . . 3
4.3. Custom Cryptographic Primitives . . . . . . . . . . . . . 4
5. Limited Capabilities . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The SSLv3 protocol has been subject to a long series of attacks, both
on its key exchange mechanism and on the encryption schemes it
supports since it was released in 1996. Despite being replaced by
TLS 1.0 [RFC2246] in 1999, and subsequently TLS 1.1 in 2002 [RFC4346]
and 1.2 in 2006 [RFC5246], availability of these replacement versions
has not been universal. As a result, many implementations of TLS
have permitted the negotiation of SSLv3.
The predecessor of SSLv3, SSL version 2, is no longer considered
sufficiently secure [RFC6176]. SSLv3 now follows.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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3. Do Not Use SSL Version 3.0
SSLv3 MUST NOT be used. Negotiation of SSLv3 from any version of TLS
MUST NOT be permitted.
Any version of TLS is more secure than SSLv3, though the highest
version available is preferable.
Pragmatically, clients MUST NOT send a ClientHello with
ClientHello.client_version set to {03,00}. Similarly, servers MUST
NOT send a ServerHello with ServerHello.server_version set to
{03,00}. Any party receiving a Hello message with the protocol
version set to {03,00} MUST respond with a "protocol_version" alert
message and close the connection.
Historically, TLS specifications were not clear on what the record
layer version number (TLSPlaintext.version) could contain when
sending ClientHello. Appendix E of [RFC5246] notes that
TLSPlaintext.version could be selected to maximize interoperability,
though no definitive value is identified as ideal. That guidance is
still applicable; therefore, TLS servers MUST accept any value
{03,XX} (including {03,00}) as the record layer version number for
ClientHello, but they MUST NOT negotiate SSLv3.
4. SSLv3 is Comprehensively Broken
4.1. Record Layer
The non-deterministic padding used in the CBC construction of SSLv3
trivially permits the recovery of plaintext [POODLE]. More
generally, the cipher block chaining (CBC) modes of SSLv3 use a
flawed MAC-then-encrypt construction that has subsequently been
replaced in TLS versions [RFC7366]. Unfortunately, the mechanism to
correct this flaw relies on extensions: a feature added in TLS 1.0.
SSLv3 cannot be updated to correct this flaw in the same way.
The flaws in the CBC modes in SSLv3 are mirrored by the weakness of
the stream ciphers it defines. Of those defined, only RC4 is
currently in widespread use. RC4, however, exhibits serious biases
and is also no longer fit for use [RFC7465].
This leaves SSLv3 with no suitable record protection mechanism.
4.2. Key Exchange
The SSLv3 key exchange is vulnerable to man-in-the-middle attacks
when renegotiation [Ray09] or session resumption [TRIPLE-HS] are
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used. Each flaw has been fixed in TLS by means of extensions.
Again, SSLv3 cannot be updated to correct these flaws.
4.3. Custom Cryptographic Primitives
SSLv3 defines custom constructions for PRF, HMAC and digital
signature primitives. Such constructions lack the deep cryptographic
scrutiny that standard constructions used by TLS have received.
Furthermore, all SSLv3 primitives rely on SHA-1 [RFC3174] and MD5
[RFC1321]: these hash algorithms are considered weak and are being
systematically replaced with stronger hash functions, such as SHA-256
[FIPS180-2].
5. Limited Capabilities
SSLv3 is unable to take advantage of the many features that have been
added to recent TLS versions. This includes the features that are
enabled by ClientHello extensions, which SSLv3 does not support.
Though SSLv3 can benefit from new cipher suites, it cannot benefit
from new cryptographic modes and features. Of these, the following
are particularly prominent:
o Authenticated Encryption with Additional Data (AEAD) modes are
added in [RFC5246].
o Elliptic Curve Diffie-Hellman (ECDH) and Digital Signature
Algorithm (ECDSA) are added in [RFC4492].
o Stateless session tickets [RFC5077].
o A datagram mode of operation, DTLS [RFC6347].
o Application layer protocol negotiation [RFC7301].
6. IANA Considerations
This document has no IANA actions.
7. Security Considerations
This entire document aims to improve security by prohibiting the use
of a protocol that is not secure.
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC6101] Freier, A., Karlton, P., and P. Kocher, "The Secure
Sockets Layer (SSL) Protocol Version 3.0", RFC 6101,
August 2011.
[RFC7366] Gutmann, P., "Encrypt-then-MAC for Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", RFC 7366, September 2014.
[RFC7465] Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465,
February 2015.
8.2. Informative References
[FIPS180-2]
Department of Commerce, National., "NIST FIPS 180-2,
Secure Hash Standard", August 2002.
[POODLE] Moeller, B., "This POODLE bites: exploiting the SSL 3.0
fallback", October 2014,
<http://googleonlinesecurity.blogspot.com/2014/10/
this-poodle-bites-exploiting-ssl-30.html>.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
[RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, September 2001.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006.
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[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, January 2008.
[RFC6176] Turner, S. and T. Polk, "Prohibiting Secure Sockets Layer
(SSL) Version 2.0", RFC 6176, March 2011.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, July 2014.
[Ray09] Ray, M., "Authentication Gap in TLS Renegotiation", 2009.
[TRIPLE-HS]
Bhargavan, K., Delignat-Lavaud, A., Fournet, C., Pironti,
A., and P-Y. Strub, "Triple Handshakes and Cookie Cutters:
Breaking and Fixing Authentication over TLS", IEEE
Symposium on Security and Privacy, 2014.
Authors' Addresses
Richard Barnes
Mozilla
Email: rlb@ipv.sx
Martin Thomson
Mozilla
Email: martin.thomson@gmail.com
Alfredo Pironti
INRIA
Email: alfredo@pironti.eu
Adam Langley
Google
Email: agl@google.com
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