Internet DRAFT - draft-lvelvindron-tls-md5-sha1-deprecate
draft-lvelvindron-tls-md5-sha1-deprecate
Internet Engineering Task Force L. Velvindron
Internet-Draft cyberstorm.mu
Updates: 5246 7525 (if approved) K. Moriarty
Intended status: Standards Track Dell EMC
Expires: November 30, 2019 A. Ghedini
Cloudflare Inc.
May 29, 2019
Deprecating MD5 and SHA-1 signature hashes in TLS 1.2
draft-lvelvindron-tls-md5-sha1-deprecate-05
Abstract
The MD5 and SHA-1 hashing algorithms are steadily weakening in
strength and their deprecation process should begin for their use in
TLS 1.2 digital signatures. However, this document does not
deprecate SHA-1 in HMAC for record protection.
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 November 30, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 2
3. Certificate Request . . . . . . . . . . . . . . . . . . . . . 3
4. Server Key Exchange . . . . . . . . . . . . . . . . . . . . . 3
5. Certificate Verify . . . . . . . . . . . . . . . . . . . . . 3
6. Updates to RFC5246 . . . . . . . . . . . . . . . . . . . . . 3
7. Updates to RFC7525 . . . . . . . . . . . . . . . . . . . . . 3
8. Security Considerations . . . . . . . . . . . . . . . . . . . 4
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 4
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
10.1. Normative References . . . . . . . . . . . . . . . . . . 4
10.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The usage of MD5 and SHA-1 for signature hashing in TLS 1.2 is
specified in RFC 5246 [RFC5246]. MD5 and SHA-1 have been proven to
be insecure, subject to collision attacks. RFC 6151 [RFC6151]
details the security considerations, including collision attacks for
MD5, published in 2011. 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. Further, in 2017,
researchers from Google and CWI Amsterdam [SHA-1-Collision] proved
SHA-1 collision attacks were practical. This document updates
RFC 5246 [RFC5246] and RFC7525 [RFC7525] in such as way that MD5 and
SHA1 MUST NOT be used for digital signatures. However, this document
does not deprecate SHA-1 in HMAC for record protection.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Signature Algorithms
Clients SHOULD NOT include MD5 and SHA-1 in signature_algorithms
extension. If a client does not send a signature_algorithms
extension, then the server MUST abort the handshake and send a
handshake_failure alert.
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3. Certificate Request
Servers SHOULD NOT include MD5 and SHA-1 in CertificateRequest
message.
4. Server Key Exchange
Servers MUST NOT include MD5 and SHA-1 in ServerKeyExchange message.
If client does receive a MD5 or SHA-1 signature in the
ServerKeyExchange message it MUST abort the connection with
handshake_failure or insufficient_security alert.
5. Certificate Verify
Clients MUST NOT include MD5 and SHA-1 in CertificateVerify message.
6. Updates to RFC5246
OLD:
In Section 7.4.1.4.1: the text should be revised from " Note: this is
a change from TLS 1.1 where there are no explicit rules, but as a
practical matter one can assume that the peer supports MD5 and SHA-
1."
NEW:
"Note: This is a change from TLS 1.1 where there are no explicit
rules, but as a practical matter one can assume that the peer
supports SHA-256."
7. Updates to RFC7525
RFC7525 [RFC7525], Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security (DTLS)
recommends use of SHA-256 as a minimum requirement. This update
moves the minimum recommendation to use stronger language deprecating
use of both SHA-1 and MD5. The prior text did not explicitly include
MD5 and this text adds it to ensure it is understood as having been
deprecated.
Section 4.3:
OLD:
When using RSA, servers SHOULD authenticate using certificates with
at least a 2048-bit modulus for the public key. In addition, the use
of the SHA-256 hash algorithm is RECOMMENDED (see [CAB-Baseline] for
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more details). Clients SHOULD indicate to servers that they request
SHA-256, by using the "Signature Algorithms" extension defined in TLS
1.2.
NEW:
servers SHOULD authenticate using certificates with at least a
2048-bit modulus for the public key.
In addition, the use of the SHA-256 hash algorithm is RECOMMENDED,
SHA-1 or MD5 MUST not be used (see [CAB-Baseline] for more details).
Clients MUST indicate to servers that they request SHA-256, by using
the "Signature Algorithms" extension defined in TLS 1.2.
8. Security Considerations
Concerns with TLS 1.2 implementations falling back to SHA-1 is an
issue. This draft 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.
9. 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 and David Cooper for their feedback.
10. References
10.1. 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>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
10.2. Informative References
[CAB-Baseline]
CA/Browser Forum, "Baseline Requirements for the Issuance
and Management of Publicly-Trusted Certificates Version
1.1.6", 2013, <https://www.cabforum.org/documents.html>.
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[NISTSP800-131A-R2]
Barker, E. and A. Roginsky, "Transitioning the Use of
Cryptographic Algorithms and Key Lengths", March 2019,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-131Ar2.pdf>.
[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>.
[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., Bursztein, E., Karpman, P., Albertini, A.,
and Y. Markov, "The first collision for full SHA-1", March
2019, <http://shattered.io/static/shattered.pdf>.
Authors' Addresses
Loganaden Velvindron
cyberstorm.mu
Rose Hill
MU
Phone: +230 59762817
Email: logan@cyberstorm.mu
Kathleen Moriarty
Dell EMC
Alessandro Ghedini
Cloudflare Inc.
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