Internet Engineering Task Force                            L. Velvindron
Internet-Draft                                             cyberstorm.mu
Updates: 5246 7525 (if approved)                             K. Moriarty
Intended status: Standards Track                                Dell EMC
Expires: July 25, 2020                                        A. Ghedini
                                                         Cloudflare Inc.
                                                        January 22, 2020


         Deprecating MD5 and SHA-1 signature hashes in TLS 1.2
                  draft-ietf-tls-md5-sha1-deprecate-02

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
   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 July 25, 2020.

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
   include Simplified BSD License text as described in Section 4.e of



Velvindron, et al.        Expires July 25, 2020                 [Page 1]


Internet-Draft      draft-ietf-tls-md5-sha1-deprecate       January 2020


   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  . . . . . . . . . . . . . . . . . . . . .   4
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   9.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   4
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   5
     10.2.  Informative References . . . . . . . . . . . . . . . . .   5
   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
   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", "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 the signature_algorithms
   extension.  If a client does not send a signature_algorithms
   extension, then the server MUST abort the handshake and send a




Velvindron, et al.        Expires July 25, 2020                 [Page 2]


Internet-Draft      draft-ietf-tls-md5-sha1-deprecate       January 2020


   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
   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 and it sent one in signature_algorithms
   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

   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

   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:

   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."





Velvindron, et al.        Expires July 25, 2020                 [Page 3]


Internet-Draft      draft-ietf-tls-md5-sha1-deprecate       January 2020


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
   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.








Velvindron, et al.        Expires July 25, 2020                 [Page 4]


Internet-Draft      draft-ietf-tls-md5-sha1-deprecate       January 2020


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>.

   [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







Velvindron, et al.        Expires July 25, 2020                 [Page 5]


Internet-Draft      draft-ietf-tls-md5-sha1-deprecate       January 2020


   Loganaden Velvindron
   cyberstorm.mu
   Rose Hill
   MU

   Phone: +230 59762817
   Email: logan@cyberstorm.mu


   Kathleen Moriarty
   Dell EMC

   Email: Kathleen.Moriarty.ietf@gmail.com


   Alessandro Ghedini
   Cloudflare Inc.

   Email: alessandro@cloudflare.com
































Velvindron, et al.        Expires July 25, 2020                 [Page 6]