Internet DRAFT - draft-ietf-tls-md5-sha1-deprecate
draft-ietf-tls-md5-sha1-deprecate
Internet Engineering Task Force L.V. Velvindron
Internet-Draft cyberstorm.mu
Updates: 5246 (if approved) K.M. Moriarty
Intended status: Standards Track CIS
Expires: 24 March 2022 A.G. Ghedini
Cloudflare Inc.
20 September 2021
Deprecating MD5 and SHA-1 signature hashes in (D)TLS 1.2
draft-ietf-tls-md5-sha1-deprecate-09
Abstract
The MD5 and SHA-1 hashing algorithms are increasingly vulnerable to
attack and this document deprecates their use in TLS 1.2 digital
signatures. However, this document does not deprecate SHA-1 in HMAC
for record protection. This document updates RFC 5246.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 24 March 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 3
3. Certificate Request . . . . . . . . . . . . . . . . . . . . . 3
4. Server Key Exchange . . . . . . . . . . . . . . . . . . . . . 3
5. Certificate Verify . . . . . . . . . . . . . . . . . . . . . 3
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 4
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
9.1. Normative References . . . . . . . . . . . . . . . . . . 4
9.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The usage of MD5 and SHA-1 for signature hashing in TLS 1.2 is
specified in [RFC5246]. MD5 and SHA-1 have been proven to be
insecure, subject to collision attacks [Wang]. In 2011, [RFC6151]
detailed the security considerations, including collision attacks for
MD5. NIST formally deprecated use of SHA-1 in 2011
[NISTSP800-131A-R2] and disallowed its use for digital signatures at
the end of 2013, based on both the Wang et al. attack and the
potential for brute-force attack. In 2016, researchers from INRIA
identified a new class of transcript collision attacks on TLS (and
other protocols) that rely on efficient collision-finding algorithms
on the underlying hash constructions [Transcript-Collision].
Further, in 2017, researchers from Google and CWI Amsterdam
[SHA-1-Collision] proved SHA-1 collision attacks were practical.
This document updates [RFC5246] in such a way that MD5 and SHA-1 MUST
NOT be used for digital signatures. However, this document does not
deprecate SHA-1 in HMAC for record protection. Note that the CABF
has also deprecated use of SHA-1 for use in certificate signatures
[CABF].
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1.1. Requirements Language
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. Signature Algorithms
Clients MUST include the signature_algorithms extension. Clients
MUST NOT include MD5 and SHA-1 in this extension.
3. Certificate Request
Servers SHOULD NOT include MD5 and SHA-1 in CertificateRequest
messages.
4. Server Key Exchange
Servers MUST NOT include MD5 and SHA-1 in ServerKeyExchange messages.
If the client receives a ServerKeyExchange message indicating MD5 or
SHA-1, then it MUST abort the connection with an illegal_parameter
alert.
5. Certificate Verify
Clients MUST NOT include MD5 and SHA-1 in CertificateVerify messages.
If a server receives a CertificateVerify message with MD5 or SHA-1 it
MUST abort the connection with an illegal_parameter alert.
6. IANA Considerations
The document updates the "TLS SignatureScheme" registry to change the
recommended status of SHA-1 based signature schemes to N (not
recommended) as defined by [RFC8447]. The following entries are to
be updated:
+========+================+=============+====================+
| Value | Description | Recommended | Reference |
+========+================+=============+====================+
| 0x0201 | rsa_pkcs1_sha1 | N | [RFC8446] [RFCTBD] |
+--------+----------------+-------------+--------------------+
| 0x0203 | ecdsa_sha1 | N | [RFC8446] [RFCTBD] |
+--------+----------------+-------------+--------------------+
Table 1
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Other entries of the registry remain the same.
IANA is also requested to update the Reference for the TLS
SignatureAlgorithm and TLS HashAlgorithm registries to refer to this
RFC:
OLD:
Reference
[RFC5246][RFC8447]
NEW:
Reference
[RFC5246][RFC8447][RFC-to-be]
7. Security Considerations
Concerns with TLS 1.2 implementations falling back to SHA-1 is an
issue. This document updates the TLS 1.2 specification to deprecate
support for MD5 and SHA-1 for digital signatures. However, this
document does not deprecate SHA-1 in HMAC for record protection.
8. Acknowledgement
The authors would like to thank Hubert Kario for his help in writing
the initial draft. We are also grateful to Daniel Migault, Martin
Thomson, Sean Turner, Christopher Wood and David Cooper for their
feedback.
9. References
9.1. 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>.
[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>.
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[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>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS
and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,
<https://www.rfc-editor.org/info/rfc8447>.
9.2. Informative References
[CABF] CA/Browser Forum, "Ballot 118 -- SHA-1 Sunset (passed)",
2014, <https://cabforum.org/2014/10/16/ballot-118-sha-
1-sunset/>.
[NISTSP800-131A-R2]
Barker, E.B. and A.R. Roginsky, "Transitioning the Use of
Cryptographic Algorithms and Key Lengths", March 2019,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-131Ar2.pdf>.
[RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, DOI 10.17487/RFC6151, March 2011,
<https://www.rfc-editor.org/info/rfc6151>.
[SHA-1-Collision]
Stevens, M.S., Bursztein, E.B., Karpman, P.K., Albertini,
A.A., and Y.M. Markov, "The first collision for full SHA-
1", March 2019, <https://eprint.iacr.org/2017/190>.
[Transcript-Collision]
Bhargavan, K.B. and G.L. Leurent, "Transcript Collision
Attacks: Breaking Authentication in TLS, IKE, and SSH",
February 2016,
<https://hal.inria.fr/hal-01244855/document>.
[Wang] Wang, X.W., Yin, Y.Y., and H.Y. Yu, "Finding Collisions in
the Full SHA-1", 2005, <https://www.iacr.org/archive/
crypto2005/36210017/36210017.pdf>.
Authors' Addresses
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Loganaden Velvindron
cyberstorm.mu
Rose Hill
Mauritius
Phone: +230 59762817
Email: logan@cyberstorm.mu
Kathleen Moriarty
Center for Internet Security
East Greenbush, NY
United States of America
Email: Kathleen.Moriarty.ietf@gmail.com
Alessandro Ghedini
Cloudflare Inc.
Email: alessandro@cloudflare.com
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