Deprecating FFDH(E) Ciphersuites in TLS
draft-bartle-tls-deprecate-ffdhe-00
Network Working Group C. Bartle
Internet-Draft Apple, Inc.
Intended status: Standards Track N. Aviram
Expires: 28 August 2021
F. Valsorda
24 February 2021
Deprecating FFDH(E) Ciphersuites in TLS
draft-bartle-tls-deprecate-ffdhe-00
Abstract
This document deprecates and discourages use of finite field and
elliptic curve Diffie Hellman cipher suites that have known
vulnerabilities or improper security properties when implemented
incorrectly.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Transport Layer
Security Working Group mailing list (tls@ietf.org), which is archived
at https://mailarchive.ietf.org/arch/browse/tls/.
Source for this draft and an issue tracker can be found at
https://github.com/cbartle891/draft-deprecate-ffdhe.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 28 August 2021.
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Table of Contents
1. Introduction
1.1. Requirements
2. Non-Ephemeral Diffie Hellman
3. Ephemeral Diffie Hellman
4. IANA Considerations
5. Security Considerations
6. Acknowledgments
7. References
7.1. Normative References
7.2. Informative References
Authors' Addresses
1. Introduction
TLS supports a variety of key exchange algorithms, including those
based on finite field and elliptic curve Diffie Hellman (DH) groups.
Each of these also come in ephemeral and non-ephemeral varieties.
Non-ephemeral DH algorithms use static DH public keys included in the
authenticating peer's certificate; see [RFC4492] for discussion. In
contrast, ephemeral DH algorithms use ephemeral DH public keys sent
in the handshake and authenticated by the peer's certificate.
Ephemeral and non-ephemeral finite field DH algorithms are called DHE
and DH, respectively, and ephemeral and non-ephemeral elliptic curve
DH algorithms are called ECDHE and ECDH, respectively [RFC4492].
In general, non-ephemeral cipher suites are not recommended due to
their lack of forward secrecy. However, as demonstrated by the
[Raccoon] attack, public key reuse, either via non-ephemeral cipher
suites or reused keys with ephemeral cipher suites, can lead to
timing side channels that may leak connection secrets. (Note that
Raccoon only applies to finite field DH cipher suites, and not those
based on elliptic curves.) While these side channels can be avoided
in implementations, doing is demonstrably difficult given the
prevalence of related side channels in TLS implementations.
Given these problems, this document updates [RFC4346], [RFC5246],
[RFC4162], [RFC6347], [RFC5932], [RFC5288], [RFC6209], [RFC6367],
[RFC8422], [RFC5289], and [RFC5469] to deprecate, prohibiting and
discouraging, cipher suites with key reuse.
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. Non-Ephemeral Diffie Hellman
Clients MUST NOT offer non-ephemeral DH cipher suites in TLS 1.0,
1.1, and 1.2 connections. This includes all cipher suites listed in
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