< draft-ietf-tls-md5-sha1-deprecate-03.txt   draft-ietf-tls-md5-sha1-deprecate-04.txt >
Internet Engineering Task Force L. Velvindron Internet Engineering Task Force L. Velvindron
Internet-Draft cyberstorm.mu Internet-Draft cyberstorm.mu
Updates: 5246 7525 (if approved) K. Moriarty Updates: 5246 7525 (if approved) K. Moriarty
Intended status: Standards Track Dell EMC Intended status: Standards Track Dell Technologies
Expires: November 15, 2020 A. Ghedini Expires: April 12, 2021 A. Ghedini
Cloudflare Inc. Cloudflare Inc.
May 14, 2020 October 9, 2020
Deprecating MD5 and SHA-1 signature hashes in TLS 1.2 Deprecating MD5 and SHA-1 signature hashes in TLS 1.2
draft-ietf-tls-md5-sha1-deprecate-03 draft-ietf-tls-md5-sha1-deprecate-04
Abstract Abstract
The MD5 and SHA-1 hashing algorithms are steadily weakening in The MD5 and SHA-1 hashing algorithms are steadily weakening in
strength and their deprecation process should begin for their use in strength and their deprecation process should begin for their use in
TLS 1.2 digital signatures. However, this document does not TLS 1.2 digital signatures. However, this document does not
deprecate SHA-1 in HMAC for record protection. deprecate SHA-1 in HMAC for record protection. This document updates
RFC 5246 and RFC 7525.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 15, 2020. This Internet-Draft will expire on April 12, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 3 2. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 3
3. Certificate Request . . . . . . . . . . . . . . . . . . . . . 3 3. Certificate Request . . . . . . . . . . . . . . . . . . . . . 3
4. Server Key Exchange . . . . . . . . . . . . . . . . . . . . . 3 4. Server Key Exchange . . . . . . . . . . . . . . . . . . . . . 3
5. Certificate Verify . . . . . . . . . . . . . . . . . . . . . 3 5. Certificate Verify . . . . . . . . . . . . . . . . . . . . . 3
6. Updates to RFC5246 . . . . . . . . . . . . . . . . . . . . . 3 6. Updates to RFC5246 . . . . . . . . . . . . . . . . . . . . . 3
7. Updates to RFC7525 . . . . . . . . . . . . . . . . . . . . . 4 7. Updates to RFC7525 . . . . . . . . . . . . . . . . . . . . . 4
8. Security Considerations . . . . . . . . . . . . . . . . . . . 4 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 4 9. Security Considerations . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . 5 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . 5 11.1. Normative References . . . . . . . . . . . . . . . . . . 5
11.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
The usage of MD5 and SHA-1 for signature hashing in TLS 1.2 is 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 specified in [RFC5246]. MD5 and SHA-1 have been proven to be
be insecure, subject to collision attacks. RFC 6151 [RFC6151] insecure, subject to collision attacks [Wang]. In 2011, [RFC6151]
details the security considerations, including collision attacks for detailed the security considerations, including collision attacks for
MD5, published in 2011. NIST formally deprecated use of SHA-1 in MD5. NIST formally deprecated use of SHA-1 in 2011
2011 [NISTSP800-131A-R2] and disallowed its use for digital [NISTSP800-131A-R2] and disallowed its use for digital signatures at
signatures at the end of 2013, based on both the Wang, et. al, attack the end of 2013, based on both the Wang, et. al, attack and the
and the potential for brute-force attack. In 2016, researchers from potential for brute-force attack. In 2016, researchers from INRIA
INRIA identified a new class of transcript collision attacks on TLS identified a new class of transcript collision attacks on TLS (and
(and other protocols) that rely on efficient collision-finding other protocols) that rely on efficient collision-finding algorithms
algorithms on the underlying hash constructions on the underlying hash constructions [Transcript-Collision].
[Transcript-Collision]. Further, in 2017, researchers from Google Further, in 2017, researchers from Google and CWI Amsterdam
and CWI Amsterdam [SHA-1-Collision] proved SHA-1 collision attacks [SHA-1-Collision] proved SHA-1 collision attacks were practical.
were practical. This document updates RFC 5246 [RFC5246] and RFC7525 This document updates [RFC5246] and [RFC7525] in such a way that MD5
[RFC7525] in such a way that MD5 and SHA-1 MUST NOT be used for and SHA-1 MUST NOT be used for digital signatures. However, this
digital signatures. However, this document does not deprecate SHA-1 document does not deprecate SHA-1 in HMAC for record protection.
in HMAC for record protection.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "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 2. Signature Algorithms
Clients MUST NOT include MD5 and SHA-1 in the signature_algorithms Clients MUST NOT include MD5 and SHA-1 in the signature_algorithms
extension. If a client does not send a signature_algorithms extension. If a client does not send a signature_algorithms
extension, then the server MUST abort the handshake and send a extension, then the server MUST abort the handshake and send a
handshake_failure alert, except when digital signatures are not used handshake_failure alert, except when digital signatures are not used
(for example, when using PSK ciphers). (for example, when using PSK ciphers).
3. Certificate Request 3. Certificate Request
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5. Certificate Verify 5. Certificate Verify
Clients MUST NOT include MD5 and SHA-1 in CertificateVerify messages. Clients MUST NOT include MD5 and SHA-1 in CertificateVerify messages.
If a server receives a CertificateVerify message with MD5 or SHA-1 it If a server receives a CertificateVerify message with MD5 or SHA-1 it
MUST abort the connection with handshake_failure or MUST abort the connection with handshake_failure or
insufficient_security alert. insufficient_security alert.
6. Updates to RFC5246 6. Updates to RFC5246
RFC5246 [RFC5246], The Transport Layer Security (TLS) Protocol [RFC5246], The Transport Layer Security (TLS) Protocol Version 1.2,
Version 1.2, suggests that implementations can assume support for MD5 suggests that implementations can assume support for MD5 and SHA-1 by
and SHA-1 by their peer. This update changes the suggestion to their peer. This update changes the suggestion to assume support for
assume support for SHA-256 instead, due to MD5 and SHA-1 being SHA-256 instead, due to MD5 and SHA-1 being deprecated.
deprecated.
In Section 7.4.1.4.1: the text should be revised from:
OLD: OLD:
In Section 7.4.1.4.1: the text should be revised from " Note: this is "Note: this is a change from TLS 1.1 where there are no explicit
a change from TLS 1.1 where there are no explicit rules, but as a rules, but as a practical matter one can assume that the peer
practical matter one can assume that the peer supports MD5 and SHA- supports MD5 and SHA- 1."
1."
NEW: NEW:
"Note: This is a change from TLS 1.1 where there are no explicit "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 rules, but as a practical matter one can assume that the peer
supports SHA-256." supports SHA-256."
7. Updates to RFC7525 7. Updates to RFC7525
RFC7525 [RFC7525], Recommendations for Secure Use of Transport Layer [RFC7525], Recommendations for Secure Use of Transport Layer Security
Security (TLS) and Datagram Transport Layer Security (DTLS) (TLS) and Datagram Transport Layer Security (DTLS) recommends use of
recommends use of SHA-256 as a minimum requirement. This update SHA-256 as a minimum requirement. This update moves the minimum
moves the minimum recommendation to use stronger language deprecating recommendation to use stronger language deprecating use of both SHA-1
use of both SHA-1 and MD5. The prior text did not explicitly include and MD5. The prior text did not explicitly include MD5 or SHA-1; and
MD5 and this text adds it to ensure it is understood as having been this text adds guidance to ensure that these algorithms have been
deprecated. deprecated..
Section 4.3: Section 4.3:
OLD: OLD:
When using RSA, servers SHOULD authenticate using certificates with When using RSA, servers SHOULD authenticate using certificates with
at least a 2048-bit modulus for the public key. In addition, the use 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 of the SHA-256 hash algorithm is RECOMMENDED (see [CAB-Baseline] for
more details). Clients SHOULD indicate to servers that they request more details). Clients SHOULD indicate to servers that they request
SHA-256, by using the "Signature Algorithms" extension defined in TLS SHA-256, by using the "Signature Algorithms" extension defined in TLS
1.2. 1.2.
NEW: NEW:
Servers SHOULD authenticate using certificates with at least a Servers SHOULD authenticate using certificates with at least a
2048-bit modulus for the public key. 2048-bit modulus for the public key.
In addition, the use of the SHA-256 hash algorithm is RECOMMENDED, 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). and SHA-1 or MD5 MUST NOT be used (see [CAB-Baseline] for more
Clients MUST indicate to servers that they request SHA-256, by using details). Clients MUST indicate to servers that they request SHA-
the "Signature Algorithms" extension defined in TLS 1.2. 256, by using the "Signature Algorithms" extension defined in TLS
1.2.
8. Security Considerations 8. 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] |
+--------+----------------+-------------+-------------------+
Other entries of the resgistry remain the same.
9. Security Considerations
Concerns with TLS 1.2 implementations falling back to SHA-1 is an Concerns with TLS 1.2 implementations falling back to SHA-1 is an
issue. This draft updates the TLS 1.2 specification to deprecate issue. This draft updates the TLS 1.2 specification to deprecate
support for MD5 and SHA-1 for digital signatures. However, this support for MD5 and SHA-1 for digital signatures. However, this
document does not deprecate SHA-1 in HMAC for record protection. document does not deprecate SHA-1 in HMAC for record protection.
9. Acknowledgement 10. Acknowledgement
The authors would like to thank Hubert Kario for his help in writing The authors would like to thank Hubert Kario for his help in writing
the initial draft. We are also grateful to Daniel Migault, Martin the initial draft. We are also grateful to Daniel Migault, Martin
Thomson and David Cooper for their feedback. Thomson and David Cooper for their feedback.
10. References 11. References
10.1. Normative References 11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <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>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>. 2015, <https://www.rfc-editor.org/info/rfc7525>.
10.2. Informative References [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>.
[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>.
11.2. Informative References
[CAB-Baseline] [CAB-Baseline]
CA/Browser Forum, "Baseline Requirements for the Issuance CA/Browser Forum, "Baseline Requirements for the Issuance
and Management of Publicly-Trusted Certificates Version and Management of Publicly-Trusted Certificates Version
1.1.6", 2013, <https://www.cabforum.org/documents.html>. 1.1.6", 2013, <https://www.cabforum.org/documents.html>.
[NISTSP800-131A-R2] [NISTSP800-131A-R2]
Barker, E. and A. Roginsky, "Transitioning the Use of Barker, E. and A. Roginsky, "Transitioning the Use of
Cryptographic Algorithms and Key Lengths", March 2019, Cryptographic Algorithms and Key Lengths", March 2019,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/ <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-131Ar2.pdf>. 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 [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms", for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, DOI 10.17487/RFC6151, March 2011, RFC 6151, DOI 10.17487/RFC6151, March 2011,
<https://www.rfc-editor.org/info/rfc6151>. <https://www.rfc-editor.org/info/rfc6151>.
[SHA-1-Collision] [SHA-1-Collision]
Stevens, M., Bursztein, E., Karpman, P., Albertini, A., Stevens, M., Bursztein, E., Karpman, P., Albertini, A.,
and Y. Markov, "The first collision for full SHA-1", March and Y. Markov, "The first collision for full SHA-1", March
2019, <http://shattered.io/static/shattered.pdf>. 2019, <http://shattered.io/static/shattered.pdf>.
[Transcript-Collision] [Transcript-Collision]
Bhargavan, K. and G. Leurent, "Transcript Collision Bhargavan, K. and G. Leurent, "Transcript Collision
Attacks: Breaking Authentication in TLS, IKE, and SSH", Attacks: Breaking Authentication in TLS, IKE, and SSH",
February 2016, <https://www.mitls.org/downloads/ February 2016, <https://www.mitls.org/downloads/
transcript-collisions.pdf>. transcript-collisions.pdf>.
[Wang] Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the
Full SHA-1", 2005.
Authors' Addresses Authors' Addresses
Loganaden Velvindron Loganaden Velvindron
cyberstorm.mu cyberstorm.mu
Rose Hill Rose Hill
MU MU
Phone: +230 59762817 Phone: +230 59762817
Email: logan@cyberstorm.mu Email: logan@cyberstorm.mu
Kathleen Moriarty Kathleen Moriarty
Dell EMC Dell Technologies
Email: Kathleen.Moriarty.ietf@gmail.com Email: Kathleen.Moriarty.ietf@gmail.com
Alessandro Ghedini Alessandro Ghedini
Cloudflare Inc. Cloudflare Inc.
Email: alessandro@cloudflare.com Email: alessandro@cloudflare.com
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