New Protocols Must Require TLS 1.3
draft-ietf-uta-require-tls13-08

Using TLS in Applications                                        R. Salz
Internet-Draft                                       Akamai Technologies
Updates: 9325 (if approved)                                    N. Aviram
Intended status: Best Current Practice                     24 March 2025
Expires: 25 September 2025

                   New Protocols Must Require TLS 1.3
                    draft-ietf-uta-require-tls13-08

Abstract

   TLS 1.2 is in use and can be configured such that it provides good
   security properties.  TLS 1.3 use is increasing, 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.  For these reasons, new protocols must require
   and assume the existence of TLS 1.3.  As DTLS 1.3 is not widely
   available or deployed, this prescription does not pertain to DTLS (in
   any DTLS version); it pertains to TLS only.

   This document updates RFC9325 and discusses post-quantum cryptography
   and fixed weaknesses in TLS 1.2 as a rationale for that update.

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 . . . . . . . . .   3
   5.  Changes to RFC 9325 . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   TLS 1.2 [TLS12] is in use and can be configured such that it provides
   good security properties.  However, this protocol version suffers
   from several deficiencies, as described in Section 6.  Note that
   addressing them usually requires bespoke configuration.

   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.

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   This document specifies that, since TLS 1.3 use is widespread, new
   protocols must require and assume its existence.  It updates
   [RFC9325] as described in Section 5.  As DTLS 1.3 is not widely
   available or deployed, this prescription does not pertain to DTLS (in
   any DTLS version); it pertains to TLS only.

   This document updates RFC9325 and discusses post-quantum cryptography
   and fixed weaknesses in TLS 1.2 as a rationale for that update.

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 (CRQC), once available,
   will have a huge impact on TLS traffic.  To mitigate this, TLS
   applications will need to migrate to post-quantum cryptography (PQC)
   [PQC].  Detailed consideration of when any application requires PQC,
   or when a CRQC is a threat they need to protect against, is beyond
   the scope of this document.

   For TLS it is important to note that the focus of these efforts
   within the TLS WG is TLS 1.3 or later, and that TLS 1.2 will not be
   supported (see [TLS12FROZEN]).  This is one more reason for new
   protocols to default to TLS 1.3, where PQC is actively being
   standardized, as this gives new applications the option to use PQC.

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 protocol and negotiation details are

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   discussed in [TLS13], Section 4.2.1 and [TLS12], Appendix E.  Many
   TLS libraries provide a way for applications to specify the range of
   versions they want, including an open interval where only the lowest
   or highest version is specified.

   If the application is using a TLS implementation that supports this,
   and if it knows that the TLS implementation will use the highest
   version supported, then clients SHOULD specify just the minimum
   version they want.  This MUST be TLS 1.3 or TLS 1.2, depending on the
   circumstances described in the above paragraphs.

5.  Changes to RFC 9325

   RFC 9325 provides recommendations for ensuring the security of
   deployed services that use TLS and, unlike this document, DTLS as
   well.  At the time it was published, it described availability of TLS
   1.3 as "widely available."  The transition and adoption mentioned in
   that documnent has grown, and this document now makes two small
   changes to the recommendations in [RFC9325], Section 3.1.1:

   *  That section says that TLS 1.3 SHOULD be supported; this document
      says that for new protocols it MUST be supported.

   *  That section says that TLS 1.2 MUST be supported; this document
      says that it MAY be supported as described above.

   Again, these changes only apply to TLS, and not DTLS.

6.  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.

   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

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   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.

   In addition, TLS 1.2 was affected by several other attacks that TLS
   1.3 is immune to: BEAST [BEAST], Logjam [WEAKDH], FREAK [FREAK], and
   SLOTH [SLOTH].

   And finally, 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.

7.  IANA Considerations

   This document makes no requests to IANA.

8.  References

8.1.  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>.

   [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>.

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   [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>.

   [TLS12FROZEN]
              Salz, R. and N. Aviram, "TLS 1.2 is in Feature Freeze",
              Work in Progress, Internet-Draft, draft-ietf-tls-tls12-
              frozen-06, 29 January 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              tls12-frozen-06>.

   [TLS13]    Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", Work in Progress, Internet-Draft, draft-
              ietf-tls-rfc8446bis-12, 17 February 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              rfc8446bis-12>.

8.2.  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>.

   [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>.

   [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>.

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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-05, 3
              September 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-tls-deprecate-obsolete-kex-05>.

   [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]      "What Is Post-Quantum Cryptography?", August 2024,
              <https://www.nist.gov/cybersecurity/what-post-quantum-
              cryptography>.

   [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>.

   [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>.

   [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>.

   [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>.

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   [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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