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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFCTBD' is mentioned on line 132, but not defined == Missing Reference: 'RFC-to-be' is mentioned on line 153, but not defined == Unused Reference: 'CAB-Baseline' is defined on line 197, but no explicit reference was found in the text ** Obsolete normative reference: RFC 5246 (Obsoleted by RFC 8446) Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force L.V. Velvindron 3 Internet-Draft cyberstorm.mu 4 Updates: 5246 (if approved) K.M. Moriarty 5 Intended status: Standards Track CIS 6 Expires: 7 March 2022 A.G. Ghedini 7 Cloudflare Inc. 8 3 September 2021 10 Deprecating MD5 and SHA-1 signature hashes in (D)TLS 1.2 11 draft-ietf-tls-md5-sha1-deprecate-08 13 Abstract 15 The MD5 and SHA-1 hashing algorithms are increasingly vulnerable to 16 attack and this document deprecates their use in TLS 1.2 digital 17 signatures. However, this document does not deprecate SHA-1 in HMAC 18 for record protection. This document updates RFC 5246. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on 7 March 2022. 37 Copyright Notice 39 Copyright (c) 2021 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 44 license-info) in effect on the date of publication of this document. 45 Please review these documents carefully, as they describe your rights 46 and restrictions with respect to this document. Code Components 47 extracted from this document must include Simplified BSD License text 48 as described in Section 4.e of the Trust Legal Provisions and are 49 provided without warranty as described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 55 2. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 3 56 3. Certificate Request . . . . . . . . . . . . . . . . . . . . . 3 57 4. Server Key Exchange . . . . . . . . . . . . . . . . . . . . . 3 58 5. Certificate Verify . . . . . . . . . . . . . . . . . . . . . 3 59 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 60 7. Security Considerations . . . . . . . . . . . . . . . . . . . 4 61 8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 4 62 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 9.1. Normative References . . . . . . . . . . . . . . . . . . 4 64 9.2. Informative References . . . . . . . . . . . . . . . . . 5 65 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 67 1. Introduction 69 The usage of MD5 and SHA-1 for signature hashing in TLS 1.2 is 70 specified in [RFC5246]. MD5 and SHA-1 have been proven to be 71 insecure, subject to collision attacks [Wang]. In 2011, [RFC6151] 72 detailed the security considerations, including collision attacks for 73 MD5. NIST formally deprecated use of SHA-1 in 2011 74 [NISTSP800-131A-R2] and disallowed its use for digital signatures at 75 the end of 2013, based on both the Wang, et. al, attack and the 76 potential for brute-force attack. In 2016, researchers from INRIA 77 identified a new class of transcript collision attacks on TLS (and 78 other protocols) that rely on efficient collision-finding algorithms 79 on the underlying hash constructions [Transcript-Collision]. 80 Further, in 2017, researchers from Google and CWI Amsterdam 81 [SHA-1-Collision] proved SHA-1 collision attacks were practical. 82 This document updates [RFC5246] in such a way that MD5 and SHA-1 MUST 83 NOT be used for digital signatures. However, this document does not 84 deprecate SHA-1 in HMAC for record protection. Note that the CABF 85 has also deprecated use of SHA-1 [CABF]. 87 1.1. Requirements Language 89 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 90 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 91 "OPTIONAL" in this document are to be interpreted as described in BCP 92 14 [RFC2119] [RFC8174] when, and only when, they appear in all 93 capitals, as shown here. 95 2. Signature Algorithms 97 Clients MUST include the signature_algorithms extension. Clients 98 MUST NOT include MD5 and SHA-1 in this extension. 100 3. Certificate Request 102 Servers SHOULD NOT include MD5 and SHA-1 in CertificateRequest 103 messages. 105 4. Server Key Exchange 107 Servers MUST NOT include MD5 and SHA-1 in ServerKeyExchange messages. 108 If no other signature algorithms are available (for example, if the 109 client does not send a signature_algorithms extension), the server 110 MUST abort the handshake with a handshake_failure alert or select a 111 different cipher suite. 113 5. Certificate Verify 115 Clients MUST NOT include MD5 and SHA-1 in CertificateVerify messages. 116 If a server receives a CertificateVerify message with MD5 or SHA-1 it 117 MUST abort the connection with handshake_failure or 118 insufficient_security alert. 120 6. IANA Considerations 122 The document updates the "TLS SignatureScheme" registry to change the 123 recommended status of SHA-1 based signature schemes to N (not 124 recommended) as defined by [RFC8447]. The following entries are to 125 be updated: 127 +========+================+=============+====================+ 128 | Value | Description | Recommended | Reference | 129 +========+================+=============+====================+ 130 | 0x0201 | rsa_pkcs1_sha1 | N | [RFC8446] [RFCTBD] | 131 +--------+----------------+-------------+--------------------+ 132 | 0x0203 | ecdsa_sha1 | N | [RFC8446] [RFCTBD] | 133 +--------+----------------+-------------+--------------------+ 135 Table 1 137 Other entries of the registry remain the same. 139 IANA is also requested to update the Reference for the TLS 140 SignatureAlgorithm and TLS HashAlgorithm registries to refer to this 141 RFC: 143 OLD: 145 Reference 147 [RFC5246][RFC8447] 149 NEW: 151 Reference 153 [RFC5246][RFC8447][RFC-to-be] 155 7. Security Considerations 157 Concerns with TLS 1.2 implementations falling back to SHA-1 is an 158 issue. This document updates the TLS 1.2 specification to deprecate 159 support for MD5 and SHA-1 for digital signatures. However, this 160 document does not deprecate SHA-1 in HMAC for record protection. 162 8. Acknowledgement 164 The authors would like to thank Hubert Kario for his help in writing 165 the initial draft. We are also grateful to Daniel Migault, Martin 166 Thomson, Sean Turner, Christopher Wood and David Cooper for their 167 feedback. 169 9. References 171 9.1. Normative References 173 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 174 Requirement Levels", BCP 14, RFC 2119, 175 DOI 10.17487/RFC2119, March 1997, 176 . 178 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 179 (TLS) Protocol Version 1.2", RFC 5246, 180 DOI 10.17487/RFC5246, August 2008, 181 . 183 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 184 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 185 May 2017, . 187 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 188 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 189 . 191 [RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS 192 and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018, 193 . 195 9.2. Informative References 197 [CAB-Baseline] 198 CA/Browser Forum, "Baseline Requirements for the Issuance 199 and Management of Publicly-Trusted Certificates Version 200 1.1.6", 2013, . 202 [CABF] CA/Browser Forum, "Ballot 118 -- SHA-1 Sunset (passed)", 203 2014, . 206 [NISTSP800-131A-R2] 207 Barker, E.B. and A.R. Roginsky, "Transitioning the Use of 208 Cryptographic Algorithms and Key Lengths", March 2019, 209 . 212 [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations 213 for the MD5 Message-Digest and the HMAC-MD5 Algorithms", 214 RFC 6151, DOI 10.17487/RFC6151, March 2011, 215 . 217 [SHA-1-Collision] 218 Stevens, M.S., Bursztein, E.B., Karpman, P.K., Albertini, 219 A.A., and Y.M. Markov, "The first collision for full SHA- 220 1", March 2019, . 222 [Transcript-Collision] 223 Bhargavan, K.B. and G.L. Leurent, "Transcript Collision 224 Attacks: Breaking Authentication in TLS, IKE, and SSH", 225 February 2016, 226 . 228 [Wang] Wang, X.W., Yin, Y.Y., and H.Y. Yu, "Finding Collisions in 229 the Full SHA-1", 2005, . 232 Authors' Addresses 234 Loganaden Velvindron 235 cyberstorm.mu 236 Rose Hill 237 Mauritius 239 Phone: +230 59762817 240 Email: logan@cyberstorm.mu 242 Kathleen Moriarty 243 Center for Interent Security 244 East Greenbush, NY 245 United States of America 247 Email: Kathleen.Moriarty.ietf@gmail.com 249 Alessandro Ghedini 250 Cloudflare Inc. 252 Email: alessandro@cloudflare.com