Deprecating Obsolete Key Exchange Methods in TLS
draft-aviram-tls-deprecate-obsolete-kex-00

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Author Nimrod Aviram 
Last updated 2021-07-09
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Network Working Group                                          N. Aviram
Internet-Draft                                               9 July 2021
Intended status: Standards Track                                        
Expires: 10 January 2022

            Deprecating Obsolete Key Exchange Methods in TLS
               draft-aviram-tls-deprecate-obsolete-kex-00

Abstract

   This document deprecates the use of RSA key exchange in TLS, and
   limits the use of Diffie Hellman key exchange over a finite field
   such as to avoid known vulnerabilities or improper security
   properties.

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
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 10 January 2022.

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   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction
     1.1.  Requirements
   2.  RSA
   3.  Ephemeral Finite Field Diffie Hellman
   4.  IANA Considerations
   5.  Security Considerations
   6.  Acknowledgments
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Author's Address

1.  Introduction

   TLS supports a variety of key exchange algorithms, including RSA and
   Diffie Hellman over a finite field, as well as elliptic curve Diffie
   Hellman (ECDH).  Diffie Hellman key exchange, over any group, may use
   either long-lived or ephemeral secrets.  Diffie Hellman key exchange
   with long-lived secrets over a finite field is already deprecated in
   [deprecate-ffdh].  This document focuses on Diffie Hellman over a
   finite field with ephemeral secrets (FFDHE), as well as RSA key
   exchange.

   Recent years have brought to light several security concerns
   regarding FFDHE key exchange that stem from implementation choices.
   Additionally, RSA key exchange suffers from security problems that
   are independent of implementation choices, as well as problems that
   stem purely from the difficulty of implementing security
   countermeasures correctly.

   At a rough glance, the problems affecting FFDHE are as follows:

   1.  FFDHE suffers from interoperability problems, because there is no
       mechanism for negotiating the group size, and some
       implementations only support small group sizes; see [RFC7919],
       Section 1.

   2.  In practice, some operators use 1024 bit FFDHE groups, since this
       is the maximum size that ensures wide support; see [RFC7919],
       Section 1.  This size leaves only a small security margin vs. the
       current discrete log record, which stands at 795 bits [DLOG795].

   3.  Expanding on the previous point, a handful of very large
       computations would allow cheaply decrypting a relatively large
       fraction of FFDHE traffic [weak-dh].

   4.  When secrets are not fully ephemeral, FFDHE suffers from the
       [Raccoon] side channel attack.

   5.  FFDHE groups may have small subgroups, which may enable several
       attacks [subgroups].

   And the problems affecting RSA key exchange are as follows:

   1.  RSA key exchange offers no forward secrecy, by construction.

   2.  RSA key exchange may be vulnerable to Bleichenbacher's attack
       [BLEI].  Experience shows that variants of this attack arise
       every few years, because implementing the relevant countermeasure
       correctly is difficult; see [ROBOT], [NEW-BLEI], [DROWN].

   3.  In addition to the above point, there is no convenient mechanism
       in TLS for domain separation of keys.  Therefore, a single
       endpoint that is vulnerable to Bleichenbacher's attack would
       affect all endpoints sharing the same RSA key; see [XPROT],
       [DROWN].

   Given these problems, this document updates [RFC4346], [RFC5246],
   [RFC4162], [RFC6347], [RFC5932], [RFC5288], [RFC6209], [RFC6367],
   [RFC8422], [RFC5289], and [RFC5469] to deprecate RSA key exchange in
   TLS, and limit use of FFDHE such that it provides acceptable security
   properties.

1.1.  Requirements

   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.

2.  RSA

   Clients and servers MUST NOT offer RSA cipher suites in TLS 1.0, 1.1,
   and 1.2 connections.  This includes all cipher suites listed in the
   following table.  Note that these cipher suites are already marked as
   not recommended in the "TLS Cipher Suites" registry.

   +-----------------------------------------+----------------------------------------------+
   | Ciphersuite                             | Reference                                    |
   +=========================================+==============================================+
   | TLS_RSA_WITH_NULL_MD5                   | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_NULL_SHA                   | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_EXPORT_WITH_RC4_40_MD5          | [RFC4346][RFC6347]                           |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_RC4_128_MD5                | [RFC5246][RFC6347]                           |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_RC4_128_SHA                | [RFC5246][RFC6347]                           |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5      | [RFC4346]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_IDEA_CBC_SHA               |[RFC5469][SC-tls-des-idea-ciphers-to-historic]|
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_EXPORT_WITH_DES40_CBC_SHA       | [RFC4346]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_DES_CBC_SHA                |[RFC5469][SC-tls-des-idea-ciphers-to-historic]|
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_3DES_EDE_CBC_SHA           | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_NULL_SHA               | [RFC4785]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_AES_128_CBC_SHA            | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_AES_256_CBC_SHA            | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_NULL_SHA256                | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_AES_128_CBC_SHA256         | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_AES_256_CBC_SHA256         | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA       | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA       | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_RC4_128_SHA            | [RFC4279][RFC6347]                           |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_3DES_EDE_CBC_SHA       | [RFC4279]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_AES_128_CBC_SHA        | [RFC4279]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_AES_256_CBC_SHA        | [RFC4279]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_SEED_CBC_SHA               | [RFC4162]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_AES_128_GCM_SHA256         | [RFC5288]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_AES_256_GCM_SHA384         | [RFC5288]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_AES_128_GCM_SHA256     | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_AES_256_GCM_SHA384     | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_AES_128_CBC_SHA256     | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_AES_256_CBC_SHA384     | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_NULL_SHA256            | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_NULL_SHA384            | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA256    | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA256    | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_ARIA_128_CBC_SHA256        | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_ARIA_256_CBC_SHA384        | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_ARIA_128_GCM_SHA256        | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_ARIA_256_GCM_SHA384        | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_ARIA_128_CBC_SHA256    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_ARIA_256_CBC_SHA384    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_ARIA_128_GCM_SHA256    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_PSK_WITH_ARIA_256_GCM_SHA384    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_CAMELLIA_128_GCM_SHA256    | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_CAMELLIA_256_GCM_SHA384    | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_RSA_PSK_WITH_CAMELLIA_128_GCM_SHA256 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_RSA_PSK_WITH_CAMELLIA_256_GCM_SHA384 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_RSA_PSK_WITH_CAMELLIA_128_CBC_SHA256 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_RSA_PSK_WITH_CAMELLIA_256_CBC_SHA384 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_AES_128_CCM                | [RFC6655]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_AES_256_CCM                | [RFC6655]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_AES_128_CCM_8              | [RFC6655]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_RSA_WITH_AES_256_CCM_8              | [RFC6655]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_RSA_PSK_WITH_CHACHA20_POLY1305_SHA256| [RFC7905]                                    |
   +-----------------------------------------+----------------------------------------------+

                                  Table 1

3.  Ephemeral Finite Field Diffie Hellman

   Clients and servers MAY offer fully ephemeral FFDHE cipher suites in
   TLS 1.0, 1.1, and 1.2 connections, under the following conditions:

   1.  The secret DH key is fully ephemeral, that is, a fresh DH
       exponent is generated for each TLS connection.  Note that this
       requirement is also specified in [deprecate-ffdh].

   2.  The group is one of the following well-known groups described in
       [RFC7919]: ffdhe2048, ffdhe3072, ffdhe4096, ffdhe6144, ffdhe8192.

   We note that previously, supporting the broadest range of clients
   would have required supporting either RSA key exchange, or 1024-bit
   FFDHE.  This is no longer the case, and it is possible to support
   most clients released since circa 2015 using 2048-bit FFDHE, or more
   modern key exchange methods, and without RSA key exchange
   [server_side_tls].

   The above requirements apply to all cipher suites listed in the
   following table.

   +-----------------------------------------+----------------------------------------------+
   | Ciphersuite                             | Reference                                    |
   +=========================================+==============================================+
   | TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA   | [RFC4346]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_DES_CBC_SHA            |[RFC5469][SC-tls-des-idea-ciphers-to-historic]|
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA       | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA   | [RFC4346]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_DES_CBC_SHA            |[RFC5469][SC-tls-des-idea-ciphers-to-historic]|
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA       | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_NULL_SHA               | [RFC4785]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_AES_128_CBC_SHA        | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_AES_128_CBC_SHA        | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_AES_256_CBC_SHA        | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_AES_256_CBC_SHA        | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_AES_128_CBC_SHA256     | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA   | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA   | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_AES_128_CBC_SHA256     | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_AES_256_CBC_SHA256     | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_AES_256_CBC_SHA256     | [RFC5246]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA   | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA   | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_RC4_128_SHA            | [RFC4279][RFC6347]                           |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA       | [RFC4279]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_AES_128_CBC_SHA        | [RFC4279]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_AES_256_CBC_SHA        | [RFC4279]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_SEED_CBC_SHA           | [RFC4162]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_SEED_CBC_SHA           | [RFC4162]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_AES_128_GCM_SHA256     | [RFC5288]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_AES_256_GCM_SHA384     | [RFC5288]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_AES_128_GCM_SHA256     | [RFC5288]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_AES_256_GCM_SHA384     | [RFC5288]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_AES_128_GCM_SHA256     | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_AES_256_GCM_SHA384     | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_AES_128_CBC_SHA256     | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_AES_256_CBC_SHA384     | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_NULL_SHA256            | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_NULL_SHA384            | [RFC5487]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA256 | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA256 | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA256 | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA256 | [RFC5932]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_ARIA_128_CBC_SHA256    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_ARIA_256_CBC_SHA384    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_ARIA_128_CBC_SHA256    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_ARIA_256_CBC_SHA384    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_ARIA_128_GCM_SHA256    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_ARIA_256_GCM_SHA384    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_ARIA_128_GCM_SHA256    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_DSS_WITH_ARIA_256_GCM_SHA384    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_ARIA_128_CBC_SHA256    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_ARIA_256_CBC_SHA384    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_ARIA_128_GCM_SHA256    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_ARIA_256_GCM_SHA384    | [RFC6209]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_RSA_WITH_CAMELLIA_128_GCM_SHA256 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_RSA_WITH_CAMELLIA_256_GCM_SHA384 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_DSS_WITH_CAMELLIA_128_GCM_SHA256 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_DSS_WITH_CAMELLIA_256_GCM_SHA384 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_PSK_WITH_CAMELLIA_128_GCM_SHA256 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_PSK_WITH_CAMELLIA_256_GCM_SHA384 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_PSK_WITH_CAMELLIA_128_CBC_SHA256 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_PSK_WITH_CAMELLIA_256_CBC_SHA384 | [RFC6367]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_AES_128_CCM            | [RFC6655]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_AES_256_CCM            | [RFC6655]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_AES_128_CCM_8          | [RFC6655]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_RSA_WITH_AES_256_CCM_8          | [RFC6655]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_AES_128_CCM            | [RFC6655]                                    |
   +-----------------------------------------+----------------------------------------------+
   | TLS_DHE_PSK_WITH_AES_256_CCM            | [RFC6655]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256| [RFC7905]                                    |
   +-----------------------------------------+----------------------------------------------+
   |TLS_DHE_PSK_WITH_CHACHA20_POLY1305_SHA256| [RFC7905]                                    |
   +-----------------------------------------+----------------------------------------------+

                                  Table 2

   Note that FFDH cipher suites are already deprecated in
   [deprecate-ffdh].

4.  IANA Considerations

   This document makes no requests to IANA.  Note that all cipher suites
   listed in Section 2 are already marked as not recommended in the "TLS
   Cipher Suites" registry.

5.  Security Considerations

   This document is entirely about security.

6.  Acknowledgments

   This document was inspired by discussion on the TLS WG mailing list
   and a suggestion by Filippo Valsorda following the release of the
   [Raccoon] attack.  Thanks to Christopher A.  Wood and Carrick D.
   Bartle for useful feedback, discussions, and ideas.

7.  References

7.1.  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/info/rfc2119>.

   [RFC4162]  Lee, H.J., Yoon, J.H., and J.I. Lee, "Addition of SEED
              Cipher Suites to Transport Layer Security (TLS)",
              RFC 4162, DOI 10.17487/RFC4162, August 2005,
              <https://www.rfc-editor.org/info/rfc4162>.

   [RFC4279]  Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
              Ciphersuites for Transport Layer Security (TLS)",
              RFC 4279, DOI 10.17487/RFC4279, December 2005,
              <https://www.rfc-editor.org/info/rfc4279>.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346,
              DOI 10.17487/RFC4346, April 2006,
              <https://www.rfc-editor.org/info/rfc4346>.

   [RFC4785]  Blumenthal, U. and P. Goel, "Pre-Shared Key (PSK)
              Ciphersuites with NULL Encryption for Transport Layer
              Security (TLS)", RFC 4785, DOI 10.17487/RFC4785, January
              2007, <https://www.rfc-editor.org/info/rfc4785>.

   [RFC5246]  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/info/rfc5246>.

   [RFC5288]  Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
              Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
              DOI 10.17487/RFC5288, August 2008,
              <https://www.rfc-editor.org/info/rfc5288>.

   [RFC5289]  Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
              256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
              DOI 10.17487/RFC5289, August 2008,
              <https://www.rfc-editor.org/info/rfc5289>.

   [RFC5469]  Eronen, P., Ed., "DES and IDEA Cipher Suites for Transport
              Layer Security (TLS)", RFC 5469, DOI 10.17487/RFC5469,
              February 2009, <https://www.rfc-editor.org/info/rfc5469>.

   [RFC5487]  Badra, M., "Pre-Shared Key Cipher Suites for TLS with SHA-
              256/384 and AES Galois Counter Mode", RFC 5487,
              DOI 10.17487/RFC5487, March 2009,
              <https://www.rfc-editor.org/info/rfc5487>.

   [RFC5932]  Kato, A., Kanda, M., and S. Kanno, "Camellia Cipher Suites
              for TLS", RFC 5932, DOI 10.17487/RFC5932, June 2010,
              <https://www.rfc-editor.org/info/rfc5932>.

   [RFC6209]  Kim, W., Lee, J., Park, J., and D. Kwon, "Addition of the
              ARIA Cipher Suites to Transport Layer Security (TLS)",
              RFC 6209, DOI 10.17487/RFC6209, April 2011,
              <https://www.rfc-editor.org/info/rfc6209>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC6367]  Kanno, S. and M. Kanda, "Addition of the Camellia Cipher
              Suites to Transport Layer Security (TLS)", RFC 6367,
              DOI 10.17487/RFC6367, September 2011,
              <https://www.rfc-editor.org/info/rfc6367>.

   [RFC6655]  McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
              Transport Layer Security (TLS)", RFC 6655,
              DOI 10.17487/RFC6655, July 2012,
              <https://www.rfc-editor.org/info/rfc6655>.

   [RFC7905]  Langley, A., Chang, W., Mavrogiannopoulos, N.,
              Strombergson, J., and S. Josefsson, "ChaCha20-Poly1305
              Cipher Suites for Transport Layer Security (TLS)",
              RFC 7905, DOI 10.17487/RFC7905, June 2016,
              <https://www.rfc-editor.org/info/rfc7905>.

   [RFC7919]  Gillmor, D., "Negotiated Finite Field Diffie-Hellman
              Ephemeral Parameters for Transport Layer Security (TLS)",
              RFC 7919, DOI 10.17487/RFC7919, August 2016,
              <https://www.rfc-editor.org/info/rfc7919>.

   [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/info/rfc8174>.

   [RFC8422]  Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
              Curve Cryptography (ECC) Cipher Suites for Transport Layer
              Security (TLS) Versions 1.2 and Earlier", RFC 8422,
              DOI 10.17487/RFC8422, August 2018,
              <https://www.rfc-editor.org/info/rfc8422>.

7.2.  Informative References

   [BLEI]     Bleichenbacher, D., "Chosen Ciphertext Attacks against
              Protocols Based on RSA Encryption Standard PKCS #1",
              Advances in Cryptology -- CRYPTO'98, LNCS vol. 1462,
              pages: 1-12 , 1998.

   [deprecate-ffdh]
              Bartle, C., Aviram, N., and F. Valsorda, "Deprecating FFDH
              Ciphersuites in TLS", June 2021,
              <https://datatracker.ietf.org/doc/draft-bartle-tls-
              deprecate-ffdhe/>.

   [DLOG795]  Boudot, F., Gaudry, P., Guillevic, A., Heninger, N.,
              Thomé, E., and P. Zimmermann, "Comparing the difficulty of
              factorization and discrete logarithm: a 240-digit
              experiment", 17 August 2020,
              <https://eprint.iacr.org/2020/697>.

   [DROWN]    Aviram, N., Schinzel, S., Somorovsky, J., Heninger, N.,
              Dankel, M., Steube, J., Valenta, L., Adrian, D.,
              Halderman, J.A., Dukhovni, V., Käsper, E., Cohney, S.,
              Engels, S., Paar, C., and Y. Shavitt, "DROWN: Breaking TLS
              using SSLv2", August 2016,
              <https://drownattack.com/drown-attack-paper.pdf>.

   [NEW-BLEI] Meyer, C., Somorovsky, J., Weiss, E., Schwenk, J.,
              Schinzel, S., and E. Tews, "Revisiting SSL/TLS
              Implementations: New Bleichenbacher Side Channels and
              Attacks", August 2014,
              <https://www.usenix.org/system/files/conference/
              usenixsecurity14/sec14-paper-meyer.pdf>.

   [Raccoon]  Merget, R., Brinkmann, M., Aviram, N., Somorovsky, J.,
              Mittmann, J., and J. Schwenk, "Raccoon Attack: Finding and
              Exploiting Most-Significant-Bit-Oracles in TLS-DH(E)", 9
              September 2020,
              <https://raccoon-attack.com/RacoonAttack.pdf>.

   [ROBOT]    Boeck, H., Somorovsky, J., and C. Young, "Return Of
              Bleichenbacher's Oracle Threat (ROBOT)", 27th USENIX
              Security Symposium , 2018.

   [SC-tls-des-idea-ciphers-to-historic]
              "Moving single-DES and IDEA TLS ciphersuites to Historic",
              25 January 2021, <https://datatracker.ietf.org/doc/status-
              change-tls-des-idea-ciphers-to-historic/>.

   [server_side_tls]
              King, A., "Server Side TLS", July 2020,
              <https://wiki.mozilla.org/Security/Server_Side_TLS>.

   [subgroups]
              Valenta, L., Adrian, D., Sanso, A., Cohney, S., Fried, J.,
              Hastings, M., Halderman, J.A., and N. Heninger, "Measuring
              small subgroup attacks against Diffie-Hellman", 15 October
              2016, <https://eprint.iacr.org/2016/995/20161017:193515>.

   [weak-dh]  Adrian, D., Bhargavan, K., Durumeric, Z., Gaudry, P.,
              Green, M., Halderman, J.A., Heninger, N., Springall, D.,
              Thomé, E., Valenta, L., VanderSloot, B., Wustrow, E.,
              Zanella-Béguelin, S., and P. Zimmermann, "Weak Diffie-
              Hellman and the Logjam Attack", October 2015,
              <https://weakdh.org/>.

   [XPROT]    Jager, T., Schwenk, J., and J. Somorovsky, "On the
              Security of TLS 1.3 and QUIC Against Weaknesses in PKCS#1
              v1.5 Encryption", Proceedings of the 22nd ACM SIGSAC
              Conference on Computer and Communications Security , 2015.

Author's Address

   Nimrod Aviram

   Email: nimrod.aviram@gmail.com