TLS 1.2 is in Feature Freeze
draft-ietf-tls-tls12-frozen-00

Transport Layer Security                                         R. Salz
Internet-Draft                                       Akamai Technologies
Intended status: Informational                                 N. Aviram
Expires: 5 October 2024                                     3 April 2024

                      TLS 1.2 is in Feature Freeze
                     draft-ietf-tls-tls12-frozen-00

Abstract

   TLS 1.2 is in widespread use and can be configured such that it
   provides good security properties.  TLS 1.3 is also in widespread use
   and fixes some known deficiencies with TLS 1.2, such as removing
   error-prone cryptographic primitives and encrypting more of the
   traffic so that it is not readable by outsiders.

   Both versions have several extension points, so items like new
   cryptographic algorithms, new supported groups (formerly "named
   curves"), etc., can be added without defining a new protocol.  This
   document specifies that outside of urgent security fixes, no new
   features will be approved for TLS 1.2.  This prescription does not
   pertain to DTLS (in any DTLS version); it pertains to TLS only.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-tls-tls12-frozen/.

   Discussion of this document takes place on the Transport Layer
   Security Working Group mailing list (mailto:tls@ietf.org), which is
   archived at https://mailarchive.ietf.org/arch/browse/tls/.  Subscribe
   at https://www.ietf.org/mailman/listinfo/tls/.

   Source for this draft and an issue tracker can be found at
   https://github.com/tlswg/tls12-frozen.

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 https://datatracker.ietf.org/drafts/current/.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Implications for post-quantum cryptography  . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   TLS 1.2 [TLS12] is in widespread use and can be configured such that
   it provides good security properties.  However, this protocol version
   suffers from several deficiencies:

   1.  While application layer traffic is always encrypted, most of the
       handshake messages are not encrypted.  Therefore, the privacy
       provided is suboptimal.  This is a protocol issue that cannot be
       addressed by configuration.

   2.  The list of cryptographic primitives specified for the protocol,
       both in-use primitives and deprecated ones, includes several
       primitives that were a source for vulnerabilities throughout the

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       years, such as RSA key exchange, CBC cipher suites, and
       problematic finite-field Diffie-Hellman group negotiation.  This
       deficiency may be addressed through proper configuration;
       however, experience shows that configuration mistakes are common,
       especially when deploying cryptography.  See Section 4 for
       elaboration.

   3.  The original protocol, as-is, does not provide security due to
       the "Renegotiation" class of attacks (see Section 4).  Rather,
       some extensions are required to provide security.

   In contrast, TLS 1.3 [TLS13] is also in widespread use and fixes most
   known deficiencies with TLS 1.2, such as encrypting more of the
   traffic so that it is not readable by outsiders and removing most
   cryptographic primitives considered dangerous.  Importantly, TLS 1.3
   enjoys robust security proofs and provides excellent security as-is.

   Both versions have several extension points, so items like new
   cryptographic algorithms, new supported groups (formerly "named
   curves"), etc., can be added without defining a new protocol.  This
   document specifies that outside of urgent security fixes, no new
   features will be approved for TLS 1.2.  This prescription does not
   pertain to DTLS (in any DTLS version); it pertains to TLS only.

2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Implications for post-quantum cryptography

   Cryptographically relevant quantum computers, once available, will
   have a huge impact on RSA, FFDH, and ECC which are currently used in
   TLS.  In 2016, the US National Institute of Standards and Technology
   started a multi-year effort to standardize algorithms that will be
   "safe" once quantum computers are feasible [PQC].  First IETF
   discussions happened around the same time [CFRGSLIDES].

   While the industry is waiting for NIST to finish standardization, the
   IETF has several efforts underway.  A working group was formed in
   early 2013 to work on use of PQC in IETF protocols, [PQUIPWG].
   Several other working groups, including TLS [TLSWG], are working on
   drafts to support hybrid algorithms and identifiers, for use during a
   transition from classic to a post-quantum world.

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   For TLS it is important to note that the focus of these efforts is
   TLS 1.3 or later.  Bluntly, post-quantum cryptography for TLS 1.2
   WILL NOT be supported (see Section 5).

4.  Security Considerations

   TLS 1.2 was specified with several cryptographic primitives and
   design choices that have historically hindered its security.  The
   purpose of this section is to briefly survey several such prominent
   problems that have affected the protocol.  It should be noted,
   however, that TLS 1.2 can be configured securely; it is merely much
   more difficult to configure it securely as opposed to using its
   modern successor, TLS 1.3.  See [RFC9325] for a more thorough guide
   on the secure deployment of TLS 1.2.

   Firstly, the TLS 1.2 protocol, without any extension points, is
   vulnerable to the renegotiation attack and the Triple Handshake
   attack.  Broadly, these attacks exploit the protocol's support for
   renegotiation in order to inject a prefix chosen by the attacker into
   the plaintext stream.  This is usually a devastating threat in
   practice, that allows e.g. obtaining secret cookies in a web setting.
   Refer to [RENEG1], [RENEG2], [TRIPLESHAKE] for elaboration.  In light
   of the above problems, [RFC5746] specifies an extension that prevents
   this category of attacks.  To securely deploy TLS 1.2, either
   renegotiation must be disabled entirely, or this extension must be
   present.  Additionally, clients must not allow servers to renegotiate
   the certificate during a connection.

   Secondly, the original key exchange methods specified for the
   protocol, namely RSA key exchange and finite field Diffie-Hellman,
   suffer from several weaknesses.  As before, to securely deploy the
   protocol, these key exchange methods must be disabled.  Refer to
   draft-obsolete-kex for elaboration (TODO I guess we will anyway wait
   for WGLC for draft-obsolete-kex, so no sense to temporarily refer to
   the draft.)

   Thirdly, symmetric ciphers which were widely-used in the protocol,
   namely RC4 and CBC cipher suites, suffer from several weaknesses.
   RC4 suffers from exploitable biases in its key stream; see [RFC7465].
   CBC cipher suites have been a source of vulnerabilities throughout
   the years.  A straightforward implementation of these cipher suites
   inherently suffers from the Lucky13 timing attack [LUCKY13].  The
   first attempt to implement the cipher suites in constant time
   introduced an even more severe vulnerability [LUCKY13FIX].  There
   have been further similar vulnerabilities throughout the years
   exploiting CBC cipher suites; refer to e.g.  [CBCSCANNING] for an
   example and a survey of similar works.

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   And lastly, historically the protocol was affected by several other
   attacks that TLS 1.3 is immune to: BEAST [BEAST], Logjam [WEAKDH],
   FREAK [FREAK], and SLOTH [SLOTH].

5.  IANA Considerations

   IANA will stop accepting registrations for any TLS parameters
   [TLS13REG] except for the following:

   *  TLS Exporter Labels

   *  TLS Application-Layer Protocol Negotiation (ALPN) Protocol IDs

   Entries in any other TLS protocol registry should have an indication
   like "For TLS 1.3 or later" in their entry.

6.  References

6.1.  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,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [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,
              <https://www.rfc-editor.org/rfc/rfc5746>.

   [RFC7465]  Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465,
              DOI 10.17487/RFC7465, February 2015,
              <https://www.rfc-editor.org/rfc/rfc7465>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC9325]  Sheffer, Y., Saint-Andre, P., and T. Fossati,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
              2022, <https://www.rfc-editor.org/rfc/rfc9325>.

   [TLS12]    Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/rfc/rfc5246>.

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   [TLS13]    Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/rfc/rfc8446>.

   [TLS13REG] Salowey, J. and S. Turner, "IANA Registry Updates for TLS
              and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,
              <https://www.rfc-editor.org/rfc/rfc8447>.

6.2.  Informative References

   [BEAST]    Duong, T. and J. Rizzo, "Here come the xor ninjas", n.d.,
              <http://www.hpcc.ecs.soton.ac.uk/dan/talks/bullrun/
              Beast.pdf>.

   [CBCSCANNING]
              Merget, R., Somorovsky, J., Aviram, N., Young, C.,
              Fliegenschmidt, J., Schwenk, J., and Y. Shavitt, "Scalable
              Scanning and Automatic Classification of TLS Padding
              Oracle Vulnerabilities", n.d.,
              <https://www.usenix.org/system/files/sec19-merget.pdf>.

   [CFRGSLIDES]
              McGrew, D., "Post Quantum Secure Cryptography Discussion",
              n.d., <https://www.ietf.org/proceedings/95/slides/slides-
              95-cfrg-4.pdf>.

   [FREAK]    Beurdouche, B., Bhargavan, K., Delignat-Lavaud, A.,
              Fournet, C., Kohlweiss, M., Pironti, A., Strub, P.-Y., and
              J. K. Zinzindohoue, "A messy state of the union: Taming
              the composite state machines of TLS", n.d.,
              <https://inria.hal.science/hal-01114250/file/messy-state-
              of-the-union-oakland15.pdf>.

   [LUCKY13]  Al Fardan, N. J. and K. G. Paterson, "Lucky Thirteen:
              Breaking the TLS and DTLS record protocols", n.d.,
              <http://www.isg.rhul.ac.uk/tls/TLStiming.pdf>.

   [LUCKY13FIX]
              Somorovsky, J., "Systematic fuzzing and testing of TLS
              libraries", n.d., <https://nds.rub.de/media/nds/
              veroeffentlichungen/2016/10/19/tls-attacker-ccs16.pdf>.

   [PQC]      "Post-Quantum Cryptography", January 2017,
              <https://csrc.nist.gov/projects/post-quantum-
              cryptography>.

   [PQUIPWG]  "Post-Quantum Use in Protocols", n.d.,
              <https://datatracker.ietf.org/wg/pquip/about/>.

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   [RENEG1]   Rescorla, E., "Understanding the TLS Renegotiation
              Attack", n.d.,
              <https://web.archive.org/web/20091231034700/
              http://www.educatedguesswork.org/2009/11/
              understanding_the_tls_renegoti.html>.

   [RENEG2]   Ray, M., "Authentication Gap in TLS Renegotiation", n.d.,
              <https://web.archive.org/web/20091228061844/
              http://extendedsubset.com/?p=8>.

   [SLOTH]    Bhargavan, K. and G. Leurent, "Transcript collision
              attacks: Breaking authentication in TLS, IKE, and SSH",
              n.d., <https://inria.hal.science/hal-01244855/file/
              SLOTH_NDSS16.pdf>.

   [TLSWG]    "Transport Layer Security", n.d.,
              <https://datatracker.ietf.org/wg/tls/about/>.

   [TRIPLESHAKE]
              "Triple Handshakes Considered Harmful Breaking and Fixing
              Authentication over TLS", n.d.,
              <https://mitls.org/pages/attacks/3SHAKE>.

   [WEAKDH]   Adrian, D., Bhargavan, K., Durumeric, Z., Gaudry, P.,
              Green, M., Halderman, J. A., Heninger, N., Springall, D.,
              Thomé, E., Valenta, L., and B. VanderSloot, "Imperfect
              forward secrecy: How Diffie-Hellman fails in practice",
              n.d.,
              <https://dl.acm.org/doi/pdf/10.1145/2810103.2813707>.

Acknowledgments

   None yet.

Authors' Addresses

   Rich Salz
   Akamai Technologies
   Email: rsalz@akamai.com

   Nimrod Aviram
   Email: nimrod.aviram@gmail.com

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