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Internet Engineering Task Force (IETF)                         R. BarnesRequest for Comments: 7568                                    M. ThomsonUpdates:5246                                                    MozillaCategory: Standards Track                                     A. PirontiISSN: 2070-1721                                                    INRIA                                                              A. Langley                                                                  Google                                                               June 2015Deprecating Secure Sockets Layer Version 3.0Abstract   The Secure Sockets Layer version 3.0 (SSLv3), as specified inRFC6101, is not sufficiently secure.  This document requires that SSLv3   not be used.  The replacement versions, in particular, Transport   Layer Security (TLS) 1.2 (RFC 5246), are considerably more secure and   capable protocols.   This document updates the backward compatibility section ofRFC 5246   and its predecessors to prohibit fallback to SSLv3.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7568.Barnes, et al.               Standards Track                    [Page 1]

RFC 7568                   SSLv3 Is Not Secure                 June 2015Copyright Notice   Copyright (c) 2015 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .33.  Do Not Use SSL Version 3.0  . . . . . . . . . . . . . . . . .34.  SSLv3 Is Comprehensively Broken . . . . . . . . . . . . . . .34.1.  Record Layer  . . . . . . . . . . . . . . . . . . . . . .34.2.  Key Exchange  . . . . . . . . . . . . . . . . . . . . . .44.3.  Custom Cryptographic Primitives . . . . . . . . . . . . .45.  Limited Capabilities  . . . . . . . . . . . . . . . . . . . .46.  Security Considerations . . . . . . . . . . . . . . . . . . .47.  References  . . . . . . . . . . . . . . . . . . . . . . . . .57.1.  Normative References  . . . . . . . . . . . . . . . . . .57.2.  Informative References  . . . . . . . . . . . . . . . . .5   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .71.  Introduction   Since it was released in 1996, the SSLv3 protocol [RFC6101] has been   subject to a long series of attacks, both on its key exchange   mechanism and on the encryption schemes it supports.  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.Barnes, et al.               Standards Track                    [Page 2]

RFC 7568                   SSLv3 Is Not Secure                 June 20152.  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 inRFC 2119 [RFC2119].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 Broken4.1.  Record Layer   The non-deterministic padding used in the Cipher Block Chaining (CBC)   construction of SSLv3 trivially permits the recovery of plaintext   [POODLE].  More generally, the 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.Barnes, et al.               Standards Track                    [Page 3]

RFC 7568                   SSLv3 Is Not Secure                 June 20154.2.  Key Exchange   The SSLv3 key exchange is vulnerable to man-in-the-middle attacks   when renegotiation [RFC5746] or session resumption [TRIPLE-HS] are   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 Pseudorandom Function (PRF),   Hashed Message Authentication Code (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 [FIPS180-4].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.  Security Considerations   This entire document aims to improve security by prohibiting the use   of a protocol that is not secure.Barnes, et al.               Standards Track                    [Page 4]

RFC 7568                   SSLv3 Is Not Secure                 June 20157.  References7.1.  Normative References   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate               Requirement Levels",BCP 14,RFC 2119,               DOI 10.17487/RFC2119, March 1997,               <http://www.rfc-editor.org/info/rfc2119>.   [RFC2246]   Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",RFC 2246, DOI 10.17487/RFC2246, January 1999,               <http://www.rfc-editor.org/info/rfc2246>.   [RFC4346]   Dierks, T. and E. Rescorla, "The Transport Layer Security               (TLS) Protocol Version 1.1",RFC 4346,               DOI 10.17487/RFC4346, April 2006,               <http://www.rfc-editor.org/info/rfc4346>.   [RFC5246]   Dierks, T. and E. Rescorla, "The Transport Layer Security               (TLS) Protocol Version 1.2",RFC 5246,               DOI 10.17487/RFC5246, August 2008,               <http://www.rfc-editor.org/info/rfc5246>.   [RFC6101]   Freier, A., Karlton, P., and P. Kocher, "The Secure               Sockets Layer (SSL) Protocol Version 3.0",RFC 6101,               DOI 10.17487/RFC6101, August 2011,               <http://www.rfc-editor.org/info/rfc6101>.   [RFC7366]   Gutmann, P., "Encrypt-then-MAC for Transport Layer               Security (TLS) and Datagram Transport Layer Security               (DTLS)",RFC 7366, DOI 10.17487/RFC7366, September 2014,               <http://www.rfc-editor.org/info/rfc7366>.   [RFC7465]   Popov, A., "Prohibiting RC4 Cipher Suites",RFC 7465,               DOI 10.17487/RFC7465, February 2015,               <http://www.rfc-editor.org/info/rfc7465>.7.2.  Informative References   [FIPS180-4] U.S. National Institute of Standards and Technology,               "Secure Hash Standard", FIPS 180-4, March 2012.   [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>.Barnes, et al.               Standards Track                    [Page 5]

RFC 7568                   SSLv3 Is Not Secure                 June 2015   [RFC1321]   Rivest, R., "The MD5 Message-Digest Algorithm",RFC 1321,               DOI 10.17487/RFC1321, April 1992,               <http://www.rfc-editor.org/info/rfc1321>.   [RFC3174]   Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm               1 (SHA1)",RFC 3174, DOI 10.17487/RFC3174, September               2001, <http://www.rfc-editor.org/info/rfc3174>.   [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, DOI               10.17487/RFC4492, May 2006,               <http://www.rfc-editor.org/info/rfc4492>.   [RFC5077]   Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,               "Transport Layer Security (TLS) Session Resumption               without Server-Side State",RFC 5077,               DOI 10.17487/RFC5077, January 2008,               <http://www.rfc-editor.org/info/rfc5077>.   [RFC5746]   Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,               "Transport Layer Security (TLS) Renegotiation Indication               Extension",RFC 5746, DOI 10.17487/RFC5746, February               2010, <http://www.rfc-editor.org/info/rfc5746>.   [RFC6176]   Turner, S. and T. Polk, "Prohibiting Secure Sockets Layer               (SSL) Version 2.0",RFC 6176, DOI 10.17487/RFC6176, March               2011, <http://www.rfc-editor.org/info/rfc6176>.   [RFC6347]   Rescorla, E. and N. Modadugu, "Datagram Transport Layer               Security Version 1.2",RFC 6347, DOI 10.17487/RFC6347,               January 2012, <http://www.rfc-editor.org/info/rfc6347>.   [RFC7301]   Friedl, S., Popov, A., Langley, A., and E. Stephan,               "Transport Layer Security (TLS) Application-Layer               Protocol Negotiation Extension",RFC 7301,               DOI 10.17487/RFC7301, July 2014,               <http://www.rfc-editor.org/info/rfc7301>.   [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.Barnes, et al.               Standards Track                    [Page 6]

RFC 7568                   SSLv3 Is Not Secure                 June 2015Authors' 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.comBarnes, et al.               Standards Track                    [Page 7]