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

   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
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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
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of



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   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  . . . . . . . . . . . . . . . . . . . .   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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