



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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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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