New Protocols Must Require TLS 1.3
draft-ietf-uta-require-tls13-01

Using TLS in Applications                                        R. Salz
Internet-Draft                                       Akamai Technologies
Updates: 9325 (if approved)                                    N. Aviram
Intended status: Standards Track                            24 July 2024
Expires: 25 January 2025

                   New Protocols Must Require TLS 1.3
                    draft-ietf-uta-require-tls13-01

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.

   Since TLS 1.3 use is widespread, new protocols must require and
   assume its existence.  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-uta-require-tls13/.

   Discussion of this document takes place on the Using TLS in
   Applications Working Group mailing list (mailto:uta@ietf.org), which
   is archived at https://mailarchive.ietf.org/arch/browse/uta/.
   Subscribe at https://www.ietf.org/mailman/listinfo/uta/.

   Source for this draft and an issue tracker can be found at
   https://github.com/richsalz/draft-use-tls13.

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.  TLS Use by Other Protocols and Applications . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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.  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 have been a source for vulnerabilities throughout

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       the years, such as RSA key exchange, CBC cipher suites, and
       problematic finite-field Diffie-Hellman group negotiation.  These
       issues could be addressed through proper configuration; however,
       experience shows that configuration mistakes are common,
       especially when deploying cryptography.  See Section 5 for
       elaboration.

   3.  The base protocol does not provide security against some types of
       attacks (see Section 5); extensions are required to provide
       security.

   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 without any
   additional configuration.

   This document specifies that, since TLS 1.3 use is widespread, new
   protocols must require and assume its existence.  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 TLS.  In 2016, the US National Institute of
   Standards and Technology (NIST) 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 2023 to work on use operational and transitional uses of PQC in
   IETF protocols, [PQUIPWG].  Several other working groups, notably
   LAMPS [LAMPSWG] and 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: TLS 1.2 WILL NOT be supported (see Section 6).
   This is one more reason for new protocols to default to TLS 1.3,
   where post-quantum cryptography is expected to be supported.

4.  TLS Use by Other Protocols and Applications

   Any new protocol that uses TLS MUST specify as its default TLS 1.3.
   For example, QUIC [QUICTLS] requires TLS 1.3 and specifies that
   endpoints MUST terminate the connection if an older version is used.

   If deployment considerations are a concern, the protocol MAY specify
   TLS 1.2 as an additional, non-default option.  As a counter example,
   the Usage Profile for DNS over TLS [DNSTLS] specifies TLS 1.2 as the
   default, while also allowing TLS 1.3.  For newer specifications that
   choose to support TLS 1.2, those preferences are to be reversed.

   The initial TLS handshake allows a client to specify which versions
   of the TLS protocol it supports and the server is intended to pick
   the highest version that it also supports.  This is known as the "TLS
   version negotiation," and many TLS libraries provide a way for
   applications to specify the range of versions.  When the API allows
   it, clients SHOULD specify just the minimum version they want.  This
   SHOULD be TLS 1.3 or TLS 1.2, depending on the circumstances
   described in the above paragraphs.

5.  Security Considerations

   TLS 1.2 was specified with several cryptographic primitives and
   design choices that have, over time, weakened 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.

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   Firstly, the TLS 1.2 protocol, without any extension points, is
   vulnerable to renegotiation attacks (see [RENEG1] and [RENEG2]) and
   the Triple Handshake attack (see [TRIPLESHAKE]).  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.  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
   used.  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.  Similarly, to securely deploy the
   protocol, these key exchange methods must be disabled.  See
   [I-D.draft-ietf-tls-deprecate-obsolete-kex] for details.

   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.

   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].

6.  IANA Considerations

   This document makes no requests to IANA.

7.  References

7.1.  Normative References

   [DNSTLS]   Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
              for DNS over TLS and DNS over DTLS", RFC 8310,
              DOI 10.17487/RFC8310, March 2018,
              <https://www.rfc-editor.org/rfc/rfc8310>.

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   [I-D.draft-ietf-tls-deprecate-obsolete-kex]
              Bartle, C. and N. Aviram, "Deprecating Obsolete Key
              Exchange Methods in TLS 1.2", Work in Progress, Internet-
              Draft, draft-ietf-tls-deprecate-obsolete-kex-04, 26 June
              2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
              tls-deprecate-obsolete-kex-04>.

   [QUICTLS]  Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
              QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
              <https://www.rfc-editor.org/rfc/rfc9001>.

   [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>.

   [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>.

7.2.  Informative References

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   [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>.

   [LAMPSWG]  "Limited Additional Mechanisms for PXIK and SMIME", n.d.,
              <https://datatracker.ietf.org/wg/lamps/about/>.

   [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/>.

   [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>.

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   [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>.

Authors' Addresses

   Rich Salz
   Akamai Technologies
   Email: rsalz@akamai.com

   Nimrod Aviram
   Email: nimrod.aviram@gmail.com

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