< draft-ietf-tls-md5-sha1-deprecate-01.txt   draft-ietf-tls-md5-sha1-deprecate-02.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 EMC
Expires: July 19, 2020 A. Ghedini Expires: July 25, 2020 A. Ghedini
Cloudflare Inc. Cloudflare Inc.
January 16, 2020 January 22, 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-01 draft-ietf-tls-md5-sha1-deprecate-02
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.
Status of This Memo Status of This Memo
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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
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
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 July 19, 2020. This Internet-Draft will expire on July 25, 2020.
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 . . . . . . . . . . . . . . . . . . . . 2 2. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 2
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 . . . . . . . . . . . . . . . . . . . . . 3 7. Updates to RFC7525 . . . . . . . . . . . . . . . . . . . . . 4
8. Security Considerations . . . . . . . . . . . . . . . . . . . 4 8. Security Considerations . . . . . . . . . . . . . . . . . . . 4
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 4 9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 4
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . 4 10.1. Normative References . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . 5 10.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
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 RFC 5246 [RFC5246]. MD5 and SHA-1 have been proven to
be insecure, subject to collision attacks. RFC 6151 [RFC6151] be insecure, subject to collision attacks. RFC 6151 [RFC6151]
details the security considerations, including collision attacks for details the security considerations, including collision attacks for
MD5, published in 2011. NIST formally deprecated use of SHA-1 in MD5, published in 2011. NIST formally deprecated use of SHA-1 in
2011 [NISTSP800-131A-R2] and disallowed its use for digital 2011 [NISTSP800-131A-R2] and disallowed its use for digital
signatures at the end of 2013, based on both the Wang, et. al, attack signatures at the end of 2013, based on both the Wang, et. al, attack
and the potential for brute-force attack. Further, in 2017, and the potential for brute-force attack. Further, in 2017,
researchers from Google and CWI Amsterdam [SHA-1-Collision] proved researchers from Google and CWI Amsterdam [SHA-1-Collision] proved
SHA-1 collision attacks were practical. This document updates SHA-1 collision attacks were practical. This document updates
RFC 5246 [RFC5246] and RFC7525 [RFC7525] in such as way that MD5 and RFC 5246 [RFC5246] and RFC7525 [RFC7525] in such as way that MD5 and
SHA1 MUST NOT be used for digital signatures. However, this document SHA-1 MUST NOT be used for digital signatures. However, this
does not deprecate SHA-1 in HMAC for record protection. document does not deprecate SHA-1 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", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Signature Algorithms 2. Signature Algorithms
Clients SHOULD NOT include MD5 and SHA-1 in signature_algorithms Clients SHOULD 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
Servers SHOULD NOT include MD5 and SHA-1 in CertificateRequest Servers SHOULD NOT include MD5 and SHA-1 in CertificateRequest
message. message.
4. Server Key Exchange 4. Server Key Exchange
Servers MUST NOT include MD5 and SHA-1 in ServerKeyExchange message. Servers MUST NOT include MD5 and SHA-1 in ServerKeyExchange message.
If client does receive a MD5 or SHA-1 signature in the If client does receive a MD5 or SHA-1 signature in the
ServerKeyExchange message it MUST abort the connection with ServerKeyExchange message and it sent one in signature_algorithms
handshake_failure or insufficient_security alert. extensions it MUST abort the connection with handshake_failure or
insufficient_security alert. If client did not send MD5 nor SHA-1
hash algorithm in signature_algorithms extension and it receives a
MD5 or SHA-1 signature in the ServerKeyExchange it MUST abort the
connection with the illegal_parameter alert.
5. Certificate Verify 5. Certificate Verify
Clients MUST NOT include MD5 and SHA-1 in CertificateVerify message. Clients MUST NOT include MD5 and SHA-1 in CertificateVerify message.
If the server receives a CertificateVerify message with MD5 or SHA-1
it MUST abort the connection with handshake_failure or
insufficient_security alert.
6. Updates to RFC5246 6. Updates to RFC5246
RFC5246 [RFC5246], The Transport Layer Security (TLS) Protocol
Version 1.2, suggests that implementations can assume support for MD5
and SHA-1 by their peer. This update changes the suggestion to
assume support for SHA-256 instead, due to MD5 and SHA-1 being
deprecated.
OLD: OLD:
In Section 7.4.1.4.1: the text should be revised from " Note: this is 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 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- practical matter one can assume that the peer 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
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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). 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 Clients MUST indicate to servers that they request SHA-256, by using
the "Signature Algorithms" extension defined in TLS 1.2. the "Signature Algorithms" extension defined in TLS 1.2.
8. Security Considerations 8. 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.
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