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New Protocols Must Require TLS 1.3

Document Type Active Internet-Draft (uta WG)
Authors Rich Salz , Nimrod Aviram
Last updated 2024-04-19
Replaces draft-rsalz-uta-require-tls13
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status (None)
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IESG IESG state I-D Exists
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Using TLS in Applications                                        R. Salz
Internet-Draft                                       Akamai Technologies
Intended status: Informational                                 N. Aviram
Expires: 21 October 2024                                   19 April 2024

                   New Protocols Must Require TLS 1.3


   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

   Discussion of this document takes place on the Using TLS in
   Applications Working Group mailing list (, which
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   Source for this draft and an issue tracker can be found at

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

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   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
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   This Internet-Draft will expire on 21 October 2024.

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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Implications for post-quantum cryptography  . . . . . . . . .   3
   4.  TLS Use by Other Protocols  . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   8
   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 encrypted.  Therefore, the privacy
       provided is suboptimal.  This is a protocol issue that cannot be
       addressed by configuration.

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   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
       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 5 for

   3.  The original protocol, as-is, does not provide security [RENEG1],
       [RENEG2], [TRIPLESHAKE].  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.

   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

2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.  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

   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 [uta], 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

   Any new protocol that uses TLS MUST specify as its default TLS 1.3
   (or a higher TLS version, when one becomes stadardized).  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.

5.  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.

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   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.

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

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,

   [QUICTLS]  Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
              QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

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   [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,

   [RFC7465]  Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465,
              DOI 10.17487/RFC7465, February 2015,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [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, <>.

   [TLS12]    Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,

   [TLS13]    Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,

7.2.  Informative References

   [BEAST]    Duong, T. and J. Rizzo, "Here come the xor ninjas", n.d.,

              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.,

              McGrew, D., "Post Quantum Secure Cryptography Discussion",
              n.d., <

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   [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.,

   [LUCKY13]  Al Fardan, N. J. and K. G. Paterson, "Lucky Thirteen:
              Breaking the TLS and DTLS record protocols", n.d.,

              Somorovsky, J., "Systematic fuzzing and testing of TLS
              libraries", n.d., <

   [PQC]      "Post=Quantum Cryptography", January 2017,

   [PQUIPWG]  "Post-Quantum Use in Protocols", n.d.,

   [RENEG1]   Rescorla, E., "Understanding the TLS Renegotiation
              Attack", n.d.,

   [RENEG2]   Ray, M., "Authentication Gap in TLS Renegotiation", n.d.,

   [SLOTH]    Bhargavan, K. and G. Leurent, "Transcript collision
              attacks: Breaking authentication in TLS, IKE, and SSH",
              n.d., <

              "Triple Handshakes Considered Harmful Breaking and Fixing
              Authentication over TLS", n.d.,

   [uta]      "Using TLS in Applications", n.d.,

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   [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",


   None yet.

Authors' Addresses

   Rich Salz
   Akamai Technologies

   Nimrod Aviram

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