Internet Engineering Task Force L. Velvindron Internet-Draft cyberstorm.mu Updates: 5246 7525 (if approved) K. Moriarty Intended status: Standards Track Dell Technologies Expires: April 12, 2021 A. Ghedini Cloudflare Inc. October 9, 2020 Deprecating MD5 and SHA-1 signature hashes in TLS 1.2 draft-ietf-tls-md5-sha1-deprecate-04 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. This document updates RFC 5246 and RFC 7525. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 12, 2021. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must Velvindron, et al. Expires April 12, 2021 [Page 1]
Internet-Draft draft-ietf-tls-md5-sha1-deprecate October 2020 include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 2. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 3 3. Certificate Request . . . . . . . . . . . . . . . . . . . . . 3 4. Server Key Exchange . . . . . . . . . . . . . . . . . . . . . 3 5. Certificate Verify . . . . . . . . . . . . . . . . . . . . . 3 6. Updates to RFC5246 . . . . . . . . . . . . . . . . . . . . . 3 7. Updates to RFC7525 . . . . . . . . . . . . . . . . . . . . . 4 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 9. Security Considerations . . . . . . . . . . . . . . . . . . . 5 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 11.1. Normative References . . . . . . . . . . . . . . . . . . 5 11.2. Informative References . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 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] and [RFC7525] 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. 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. Velvindron, et al. Expires April 12, 2021 [Page 2]
Internet-Draft draft-ietf-tls-md5-sha1-deprecate October 2020 2. 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, then the server MUST abort the handshake and send a handshake_failure alert, except when digital signatures are not used (for example, when using PSK ciphers). 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 a client receives a MD5 or SHA-1 signature in a ServerKeyExchange message it MUST abort the connection with the 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 handshake_failure or insufficient_security alert. 6. Updates to 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. In Section 7.4.1.4.1: the text should be revised from: OLD: "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." Velvindron, et al. Expires April 12, 2021 [Page 3]
Internet-Draft draft-ietf-tls-md5-sha1-deprecate October 2020 7. Updates to 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 or SHA-1; and this text adds guidance to ensure that these algorithms have 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 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; and 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. 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. Velvindron, et al. Expires April 12, 2021 [Page 4]
Internet-Draft draft-ietf-tls-md5-sha1-deprecate October 2020 9. 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. 10. 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. 11. References 11.1. 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>. [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>. [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] 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>. Velvindron, et al. Expires April 12, 2021 [Page 5]
Internet-Draft draft-ietf-tls-md5-sha1-deprecate October 2020 [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>. [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>. [Transcript-Collision] Bhargavan, K. and G. Leurent, "Transcript Collision Attacks: Breaking Authentication in TLS, IKE, and SSH", February 2016, <https://www.mitls.org/downloads/ transcript-collisions.pdf>. [Wang] Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the Full SHA-1", 2005. Authors' Addresses Loganaden Velvindron cyberstorm.mu Rose Hill MU Phone: +230 59762817 Email: logan@cyberstorm.mu Kathleen Moriarty Dell Technologies Email: Kathleen.Moriarty.ietf@gmail.com Alessandro Ghedini Cloudflare Inc. Email: alessandro@cloudflare.com Velvindron, et al. Expires April 12, 2021 [Page 6]
