



Network Working Group                                        L. Bruckert
Internet-Draft                                                 J. Merkle
Intended status: Informational                 secunet Security Networks
Expires: March 29, 2020                                       M. Lochter
                                                                     BSI
                                                      September 26, 2019


  ECC Brainpool Curves for Transport Layer Security (TLS) Version 1.3
                 draft-bruckert-brainpool-for-tls13-07

Abstract

   ECC Brainpool curves were an option for authentication and key
   exchange in the Transport Layer Security (TLS) protocol version 1.2,
   but were deprecated by the IETF for use with TLS version 1.3 because
   they had little usage.  However, these curves have not been shown to
   have significant cryptographical weaknesses, and there is some
   interest in using several of these curves in TLS 1.3.

   This document provides the necessary protocol mechanisms for using
   ECC Brainpool curves in TLS 1.3.  This approach is not endorsed by
   the IETF.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on March 29, 2020.

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
   Provisions Relating to IETF Documents



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   (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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Terminology  . . . . . . . . . . . . . . . . . .   3
   3.  Brainpool NamedGroup Types  . . . . . . . . . . . . . . . . .   3
   4.  Brainpool SignatureScheme Types . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Test Vectors . . . . . . . . . . . . . . . . . . . .   8
     A.1.  256 Bit Curve . . . . . . . . . . . . . . . . . . . . . .   8
     A.2.  384 Bit Curve . . . . . . . . . . . . . . . . . . . . . .   9
     A.3.  512 Bit Curve . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   [RFC5639] specifies a new set of elliptic curve groups over finite
   prime fields for use in cryptographic applications.  These groups,
   denoted as ECC Brainpool curves, were generated in a verifiably
   pseudo-random way and comply with the security requirements of
   relevant standards from ISO [ISO1] [ISO2], ANSI [ANSI1], NIST [FIPS],
   and SecG [SEC2].

   [RFC8422] defines the usage of elliptic curves for authentication and
   key agreement in TLS 1.2 and earlier versions, and [RFC7027] defines
   the usage of the ECC Brainpool curves for authentication and key
   exchange in TLS.  The latter is applicable to TLS 1.2 and earlier
   versions, but not to TLS 1.3 that deprecates the ECC Brainpool Curve
   IDs defined in [RFC7027] due to the lack of widespread deployment
   However, there is some interest in using these curves in TLS 1.3.

   The negotiation of ECC Brainpool Curves for key exchange in TLS 1.3
   according to [RFC8446] requires the definition and assignment of
   additional NamedGroup IDs.  This document provides the necessary
   definition and assignment of additional SignatureScheme IDs for using
   three ECC Brainpool Curves from [RFC5639].




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   This approach is not endorsed by the IETF.  Implementers and
   deployers need to be aware of the strengths and weaknesses of all
   security mechanisms that they use.

2.  Requirements Terminology

   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].

3.  Brainpool NamedGroup Types

   According to [RFC8446], the "supported_groups" extension is used for
   the negotiation of Diffie-Hellman groups and elliptic curve groups
   for key exchange during a handshake starting a new TLS session.  This
   document adds new named groups for three elliptic curves defined in
   [RFC5639] to the "supported_groups" extension as follows.

           enum {
                brainpoolP256r1tls13(31),
                brainpoolP384r1tls13(32),
                brainpoolP512r1tls13(33)
           } NamedGroup;

   The encoding of ECDHE parameters for sec256r1, secp384r1, and
   secp521r1 as defined in section 4.2.8.2 of [RFC8446] also applies to
   this document.

   Test vectors for a Diffie-Hellman key exchange using these elliptic
   curves are provided in Appendix A.

4.  Brainpool SignatureScheme Types

   According to [RFC8446], the name space SignatureScheme is used for
   the negotiation of elliptic curve groups for authentication via the
   "signature_algorithms" extension.  Besides, it is required to specify
   the hash function that is used to hash the message before signing.
   This document adds new SignatureScheme types for three elliptic
   curves defined in [RFC5639] as follows.

           enum {
                ecdsa_brainpoolP256r1tls13_sha256(0x081A),
                ecdsa_brainpoolP384r1tls13_sha384(0x081B),
                ecdsa_brainpoolP512r1tls13_sha512(0x081C)
           } SignatureScheme;






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5.  IANA Considerations

   IANA is requested to update the references for the ECC Brainpool
   curves listed in the Transport Layer Security (TLS) Parameters
   registry "TLS Supported Groups" [IANA-TLS] to this document.

   +-------+----------------------+---------+-------------+-----------+
   | Value |     Description      | DTLS-OK | Recommended | Reference |
   +-------+----------------------+---------+-------------+-----------+
   |   31  | brainpoolP256r1tls13 |    Y    |      N      |  This doc |
   |       |                      |         |             |           |
   |   32  | brainpoolP384r1tls13 |    Y    |      N      |  This doc |
   |       |                      |         |             |           |
   |   33  | brainpoolP512r1tls13 |    Y    |      N      |  This doc |
   +-------+----------------------+---------+-------------+-----------+

                                  Table 1

   IANA is requested to update the references for the ECC Brainpool
   curves in the Transport Layer Security (TLS) Parameters registry "TLS
   SignatureScheme" [IANA-TLS] to this document.

   +--------+----------------------+---------+-------------+-----------+
   | Value  |     Description      | DTLS-OK | Recommended | Reference |
   +--------+----------------------+---------+-------------+-----------+
   | 0x081A | ecdsa_brainpoolP256r |    Y    |      N      |  This doc |
   |        |    1tls13_sha256     |         |             |           |
   |        |                      |         |             |           |
   | 0x081B | ecdsa_brainpoolP384r |    Y    |      N      |  This doc |
   |        |    1tls13_sha384     |         |             |           |
   |        |                      |         |             |           |
   | 0x081C | ecdsa_brainpoolP512r |    Y    |      N      |  This doc |
   |        |    1tls13_sha512     |         |             |           |
   +--------+----------------------+---------+-------------+-----------+

                                  Table 2

6.  Security Considerations

   The security considerations of [RFC8446] apply accordingly.

   The confidentiality, authenticity and integrity of the TLS
   communication is limited by the weakest cryptographic primitive
   applied.  In order to achieve a maximum security level when using one
   of the elliptic curves from Table 1 for key exchange and / or one of
   the signature algorithms from Table 2 for authentication in TLS, the
   key derivation function, the algorithms and key lengths of symmetric
   encryption and message authentication as well as the algorithm, bit



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   length and hash function used for signature generation should be
   chosen at commensurate strengths, for example according to the
   recommendations of [NIST800-57] and [RFC5639].  Furthermore, the
   private Diffie-Hellman keys should be generated from a random
   keystream with a length equal to the length of the order of the group
   E(GF(p)) defined in [RFC5639].  The value of the private Diffie-
   Hellman keys should be less than the order of the group E(GF(p)).

   When using ECDHE key agreement with the curves brainpoolP256r1tls13,
   brainpoolP384r1tls13 or brainpoolP512r1tls13, the peers MUST validate
   each other's public value Q by ensuring that the point is a valid
   point on the elliptic curve.  If this check is not conducted, an
   attacker can force the key exchange into a small subgroup, and the
   resulting shared secret can be guessed with significantly less
   effort.

   Implementations of elliptic curve cryptography for TLS may be
   susceptible to side-channel attacks.  Particular care should be taken
   for implementations that internally transform curve points to points
   on the corresponding "twisted curve", using the map (x',y') = (x*Z^2,
   y*Z^3) with the coefficient Z specified for that curve in [RFC5639],
   in order to take advantage of an an efficient arithmetic based on the
   twisted curve's special parameters (A = -3): although the twisted
   curve itself offers the same level of security as the corresponding
   random curve (through mathematical equivalence), arithmetic based on
   small curve parameters may be harder to protect against side-channel
   attacks.  General guidance on resistence of elliptic curve
   cryptography implementations against side-channel-attacks is given in
   [BSI1] and [HMV].

7.  References

7.1.  Normative References

   [IANA-TLS]
              Internet Assigned Numbers Authority, "Transport Layer
              Security (TLS) Parameters",
              <http://www.iana.org/assignments/tls-parameters/tls-
              parameters.xml>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5639]  Lochter, M. and J. Merkle, "Elliptic Curve Cryptography
              (ECC) Brainpool Standard Curves and Curve Generation",
              RFC 5639, March 2010.





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   [RFC7027]  Merkle, J. and M. Lochter, "Elliptic Curve Cryptography
              (ECC) Brainpool Curves for Transport Layer Security
              (TLS)", RFC 7027, DOI 10.17487/RFC7027, October 2013,
              <https://www.rfc-editor.org/info/rfc7027>.

   [RFC8422]  Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
              Curve Cryptography (ECC) Cipher Suites for Transport Layer
              Security (TLS) Versions 1.2 and Earlier", RFC 8422,
              DOI 10.17487/RFC8422, August 2018,
              <https://www.rfc-editor.org/info/rfc8422>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

7.2.  Informative References

   [ANSI1]    American National Standards Institute, "Public Key
              Cryptography For The Financial Services Industry: The
              Elliptic Curve Digital Signature Algorithm (ECDSA)",
              ANSI X9.62, 2005.

   [BSI1]     Bundesamt fuer Sicherheit in der Informationstechnik,
              "Minimum Requirements for Evaluating Side-Channel Attack
              Resistance of Elliptic Curve Implementations", July 2011.

   [FIPS]     National Institute of Standards and Technology, "Digital
              Signature Standard (DSS)", FIPS PUB 186-2, December 1998.

   [HMV]      Hankerson, D., Menezes, A., and S. Vanstone, "Guide to
              Elliptic Curve Cryptography", Springer Verlag, 2004.

   [ISO1]     International Organization for Standardization,
              "Information Technology - Security Techniques - Digital
              Signatures with Appendix - Part 3: Discrete Logarithm
              Based Mechanisms", ISO/IEC 14888-3, 2006.

   [ISO2]     International Organization for Standardization,
              "Information Technology - Security Techniques -
              Cryptographic Techniques Based on Elliptic Curves - Part
              2: Digital signatures", ISO/IEC 15946-2, 2002.

   [NIST800-57]
              National Institute of Standards and Technology,
              "Recommendation for Key Management - Part 1: General
              (Revised)", NIST Special Publication 800-57, January 2016.





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   [SEC1]     Certicom Research, "Elliptic Curve Cryptography",
              Standards for Efficient Cryptography (SEC) 1, September
              2000.

   [SEC2]     Certicom Research, "Recommended Elliptic Curve Domain
              Parameters", Standards for Efficient Cryptography (SEC) 2,
              September 2000.












































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Appendix A.  Test Vectors

   This non-normative Appendix provides some test vectors for example
   Diffie-Hellman key exchanges using each of the curves defined in
   Table 1 .  In all of the following sections the following notation is
   used:

      d_A: the secret key of party A

      x_qA: the x-coordinate of the public key of party A

      y_qA: the y-coordinate of the public key of party A

      d_B: the secret key of party B

      x_qB: the x-coordinate of the public key of party B

      y_qB: the y-coordinate of the public key of party B

      x_Z: the x-coordinate of the shared secret that results from
      completion of the Diffie-Hellman computation, i.e. the hex
      representation of the pre-master secret

      y_Z: the y-coordinate of the shared secret that results from
      completion of the Diffie-Hellman computation

   The field elements x_qA, y_qA, x_qB, y_qB, x_Z, y_Z are represented
   as hexadecimal values using the FieldElement-to-OctetString
   conversion method specified in [SEC1].

A.1.  256 Bit Curve

   Curve brainpoolP256r1

      dA =
      81DB1EE100150FF2EA338D708271BE38300CB54241D79950F77B063039804F1D

      x_qA =
      44106E913F92BC02A1705D9953A8414DB95E1AAA49E81D9E85F929A8E3100BE5

      y_qA =
      8AB4846F11CACCB73CE49CBDD120F5A900A69FD32C272223F789EF10EB089BDC

      dB =
      55E40BC41E37E3E2AD25C3C6654511FFA8474A91A0032087593852D3E7D76BD3

      x_qB =
      8D2D688C6CF93E1160AD04CC4429117DC2C41825E1E9FCA0ADDD34E6F1B39F7B



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      y_qB =
      990C57520812BE512641E47034832106BC7D3E8DD0E4C7F1136D7006547CEC6A

      x_Z =
      89AFC39D41D3B327814B80940B042590F96556EC91E6AE7939BCE31F3A18BF2B

      y_Z =
      49C27868F4ECA2179BFD7D59B1E3BF34C1DBDE61AE12931648F43E59632504DE

A.2.  384 Bit Curve

   Curve brainpoolP384r1

      dA = 1E20F5E048A5886F1F157C74E91BDE2B98C8B52D58E5003D57053FC4B0BD6
      5D6F15EB5D1EE1610DF870795143627D042

      x_qA = 68B665DD91C195800650CDD363C625F4E742E8134667B767B1B47679358
      8F885AB698C852D4A6E77A252D6380FCAF068

      y_qA = 55BC91A39C9EC01DEE36017B7D673A931236D2F1F5C83942D049E3FA206
      07493E0D038FF2FD30C2AB67D15C85F7FAA59

      dB = 032640BC6003C59260F7250C3DB58CE647F98E1260ACCE4ACDA3DD869F74E
      01F8BA5E0324309DB6A9831497ABAC96670

      x_qB = 4D44326F269A597A5B58BBA565DA5556ED7FD9A8A9EB76C25F46DB69D19
      DC8CE6AD18E404B15738B2086DF37E71D1EB4

      y_qB = 62D692136DE56CBE93BF5FA3188EF58BC8A3A0EC6C1E151A21038A42E91
      85329B5B275903D192F8D4E1F32FE9CC78C48

      x_Z = 0BD9D3A7EA0B3D519D09D8E48D0785FB744A6B355E6304BC51C229FBBCE2
      39BBADF6403715C35D4FB2A5444F575D4F42

      y_Z = 0DF213417EBE4D8E40A5F76F66C56470C489A3478D146DECF6DF0D94BAE9
      E598157290F8756066975F1DB34B2324B7BD

A.3.  512 Bit Curve

   Curve brainpoolP512r1

      dA = 16302FF0DBBB5A8D733DAB7141C1B45ACBC8715939677F6A56850A38BD87B
      D59B09E80279609FF333EB9D4C061231FB26F92EEB04982A5F1D1764CAD5766542
      2

      x_qA = 0A420517E406AAC0ACDCE90FCD71487718D3B953EFD7FBEC5F7F27E28C6
      149999397E91E029E06457DB2D3E640668B392C2A7E737A7F0BF04436D11640FD0
      9FD



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      y_qA = 72E6882E8DB28AAD36237CD25D580DB23783961C8DC52DFA2EC138AD472
      A0FCEF3887CF62B623B2A87DE5C588301EA3E5FC269B373B60724F5E82A6AD147F
      DE7

      dB = 230E18E1BCC88A362FA54E4EA3902009292F7F8033624FD471B5D8ACE49D1
      2CFABBC19963DAB8E2F1EBA00BFFB29E4D72D13F2224562F405CB80503666B2542
      9

      x_qB = 9D45F66DE5D67E2E6DB6E93A59CE0BB48106097FF78A081DE781CDB31FC
      E8CCBAAEA8DD4320C4119F1E9CD437A2EAB3731FA9668AB268D871DEDA55A54731
      99F

      y_qB = 2FDC313095BCDD5FB3A91636F07A959C8E86B5636A1E930E8396049CB48
      1961D365CC11453A06C719835475B12CB52FC3C383BCE35E27EF194512B7187628
      5FA

      x_Z = A7927098655F1F9976FA50A9D566865DC530331846381C87256BAF322624
      4B76D36403C024D7BBF0AA0803EAFF405D3D24F11A9B5C0BEF679FE1454B21C4CD
      1F

      y_Z = 7DB71C3DEF63212841C463E881BDCF055523BD368240E6C3143BD8DEF8B3
      B3223B95E0F53082FF5E412F4222537A43DF1C6D25729DDB51620A832BE6A26680
      A2

Authors' Addresses

   Leonie Bruckert
   secunet Security Networks
   Ammonstr. 74
   01067 Dresden
   Germany

   Phone: +49 201 5454 3819
   EMail: leonie.bruckert@secunet.com


   Johannes Merkle
   secunet Security Networks
   Mergenthaler Allee 77
   65760 Eschborn
   Germany

   Phone: +49 201 5454 3091
   EMail: johannes.merkle@secunet.com







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   Manfred Lochter
   BSI
   Postfach 200363
   53133 Bonn
   Germany

   Phone: +49 228 9582 5643
   EMail: manfred.lochter@bsi.bund.de











































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