One document matched: draft-josefsson-tls-eddsa2-01.xml

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<?rfc symrefs="yes"?>

<rfc category="std"
     ipr="trust200902"
     docName="draft-josefsson-tls-eddsa2-01" >
  
  <front>
    
    <title abbrev="EdDSA and Ed25519 for TLS">
      EdDSA and Ed25519 for Transport Layer Security (TLS)
    </title>

    <author fullname="Simon Josefsson" initials="S." surname="Josefsson">
      <organization>SJD AB</organization>
      <address>
        <email>simon@josefsson.org</email>
      </address>
    </author>

    <date month="June" year="2015" />

    <keyword>TLS, Elliptic Curve Cryptography, EdDSA, Ed25519,
    Curve25519, X25519</keyword>

    <abstract>

      <t>This document introduce the public-key signature algorithm
      EdDSA for use in Transport Layer Security (TLS).  By defining
      new SignatureAlgorithm, NamedCurve and ECPointFormat
      enumerations, we describe how EdDSA and Ed25519 is used for
      digital signatures in the existing ECDSA cipher suites.  This is
      intended to work with any version of TLS and Datagram TLS.</t>
      
    </abstract>

  </front>

  <middle>

    <section title="Introduction">

      <t><xref target="RFC5246">TLS</xref> and <xref
      target="RFC6347">DTLS</xref> support different key exchange
      algorithms and authentication mechanisms, and define the
      SignatureAlgorithm enumeration for different signature
      algorithms.  In <xref target="RFC4492">TLS-ECC</xref>, key
      exchange and authentication using ECC is specified, where the
      NamedCurve and ECPointFormat registries and associated TLS
      extensions are introduced.</t>

      <t>This document describes how to use <xref
      target="I-D.josefsson-eddsa-ed25519">EdDSA and Ed25519</xref> as
      a new authentication mechanism in TLS.  It define new
      SignatureAlgorithm, NamedCurve and ECPointFormat enumeration
      values and describe how these are used to negotiate EdDSA-based
      signatures.</t>

      <t>The goal is that all existing ECDSA cipher suites will, when
      the EdDSA SignatureAlgorithm is negotiated, use EdDSA instead of
      the traditional ECDSA signature algorithm.</t>

      <t>This document is a self-contained alternative to
      draft-josefsson-tls-eddsa.  This document reuse the ECDSA cipher
      suites for EdDSA, whereas draft-josefsson-tls-eddsa specify new
      cipher suites for EdDSA.  It is an open issue which approach is
      to be prefered.</t>

      <section title="Requirements Terminology">

        <t>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 <xref target="RFC2119" />.</t>

      </section>
      
    </section>
    
    <section title="EdDSA SignatureAlgorithm"
	     anchor="SignatureAlgorithm">

      <t>Negotiation of the authentication mechanism is signalled by
      sending a SignatureAlgorithm value.  Here we extend this
      enumeration for EdDSA.</t>

      <figure>
        <artwork><![CDATA[
   enum {
      eddsa(4)
   } SignatureAlgorithm;
]]></artwork>
      </figure>

      <t>EdDSA is suitable for use with TLS <xref target='RFC5246'/>
      and DTLS <xref target='RFC6347'/>.</t>

      <t>Note that EdDSA merely signals which signature algorithm to
      use, it does not imply any curve or hash parameter choice.</t>
      
    </section>

    <section title="EdDSA Public-key format"
	     anchor="ECPointFormat">

      <t>This section defines a new point format suitable to encode
      EdDSA public keys, as well as an identifier to negotiate this
      new format in TLS, and includes guidance on their use.</t>

      <t>The curves defined in <xref target="RFC4492" /> define a
      public key as a point on the curve. In order to exchange public
      keys, the points are serialized as a string of bytes.  Since
      EdDSA public keys already are string of bytes, no serialization
      is needed.</t>

      <t>We define the following ECPointFormat value for raw binary
      EdDSA public keys.</t>

      <figure>
        <artwork><![CDATA[
      enum {
           eddsa_public_key(4),
      } ECPointFormat;
]]></artwork>
      </figure>

      <t>When included in a ServerKeyExchange or ClientKeyExchange
      message, the public key is wrapped in an ECPoint structure as
      defined in <xref target="RFC4492" />, whose payload is as
      described above.</t>

      <t>For example, a Ed25519 public key with value
      D75A980182B10AB7D54BFED3C964073A0EE172F3DAA62325AF021A68F707511A
      appears on the wire as follows (including the length byte of
      ECPoint.point).</t>

        <figure>
          <artwork><![CDATA[
	  20 D7 5A 98 01 82 B1 0A B7 D5 4B FE D3 C9 64 07
	  3A 0E E1 72 F3 DA A6 23 25 AF 02 1A 68 F7 07 51
	  1A
          ]]></artwork>
        </figure>
      
    </section>

    <section title="Ed25519 NamedCurve"
	     anchor="NamedCurve">
  
      <t>Negotiation the elliptic curve is signalled with the
      Supported Elliptic Curves Extension extension.  Here we extend
      the NamedCurve enumeration for EdDSA with the Ed25519 parameter
      choice.</t>

      <figure>
        <artwork><![CDATA[
   enum {
      ed25519(5)
   } NamedCurve;
]]></artwork>
      </figure>
      
    </section>
    
    <section title="Using EdDSA in a handshake">

      <t>The following describe how EdDSA is used in a handshake. For
      ease of explanation, we assume a full handshake.  <xref
      target="RFC4492" /> describes the semantics of ECC in TLS,
      including how resumed handshakes work, and this document refer
      to it for a complete discussion.</t>
      
      <t>A client that wish to negotiate use of EdDSA in a handshake
      MUST offer a ECDSA key exchange algorithm and send, in the same
      way as is done for other Signature Algorithms in ECDSA, a
      Signature Algorithm extension that include the "eddsa"
      SignatureAlgorithm value.  The HashAlgorithm, NamedCurve and
      ECPointFormat types are also required, but depend on the actual
      EdDSA parameter choices.</t>

      <t>The HashAlgorithm value to specify for Ed25519 MUST be
      "sha512", to indicate use of Ed25519-SHA-512 as defined in <xref
      target="I-D.josefsson-eddsa-ed25519"/>.  The meaning of using a
      "eddsa" SignatureAlgorithm with other HashAlgorithms will
      require additional specification to specify the meaning.</t>

      <t>The Supported Elliptic Curves Extension ("NamedCurve") must
      also contain the relevant curve.  Currently the only curve
      applicable to EdDSA is the "ed25519" NamedCurve value defined in
      this document.  This is used to indicate request for
      Ed25519.</t>

      <t>The client MUST also include a Supported Point Formats
      Extension ("ECPointFormat") that contains the "eddsa_public_key"
      value.</t>
      
    </section>
    
    <section title="IANA Considerations">

      <t>IANA is requested to assign a number for EdDSA described in
      <xref target='SignatureAlgorithm' /> to the Transport Layer
      Security (TLS) Parameters <xref target='IANA-TLS' /> registry
      under "SignatureAlgorithm" as follows.</t>

      <texttable>
	<preamble></preamble>
	<ttcol align='center'>Value</ttcol>
	<ttcol align='center'>Description</ttcol>
	<ttcol align='center'>DTLS-OK</ttcol>
	<ttcol align='center'>Reference</ttcol>
	<c>4</c>
	<c>eddsa</c>
	<c>Y</c>
	<c>This doc</c>
	<postamble></postamble>
      </texttable>

      <t>IANA is requested to assign a number for Ed25519 described in
      <xref target='NamedCurve' /> to the Transport Layer Security
      (TLS) Parameters registry EC Named Curve <xref target='IANA-TLS'
      /> as follows.</t>

      <texttable>
	<preamble></preamble>
	<ttcol align='center'>Value</ttcol>
	<ttcol align='center'>Description</ttcol>
	<ttcol align='center'>DTLS-OK</ttcol>
	<ttcol align='center'>Reference</ttcol>
	<c>5</c>
	<c>ed25519</c>
	<c>Y</c>
	<c>This doc</c>
	<postamble></postamble>
      </texttable>

      <t>IANA is requested to assign a number for eddsa_public_key
      described in <xref target='ECPointFormat' /> to the Transport
      Layer Security (TLS) Parameters registry EC Point Format <xref
      target='IANA-TLS' /> as follows. </t>

      <texttable>
	<preamble></preamble>
	<ttcol align='center'>Value</ttcol>
	<ttcol align='center'>Description</ttcol>
	<ttcol align='center'>DTLS-OK</ttcol>
	<ttcol align='center'>Reference</ttcol>
	<c>4</c>
	<c>eddsa_public_key</c>
	<c>Y</c>
	<c>This doc</c>
	<postamble></postamble>
      </texttable>

    </section>

    <section title="Security Considerations">

      <t>The security considerations of <xref
      target="RFC5246">TLS</xref>, <xref target="RFC6347">DTLS</xref>,
      <xref target="RFC4492">TLS-ECC</xref>, and <xref
      target="I-D.josefsson-eddsa-ed25519">EdDSA and Ed25519</xref>
      are inherited.</t>

      <t>As with all cryptographic algorithms and security protocols,
      the reader should stay informed about new research insights into
      the security of the algorithms and protocols involved.</t>

      <t>While discussed in the EdDSA/Ed25519 specification and
      papers, we would like to stress the significance of
      EdDSA/Ed25519 implementation security.  In particular,
      implementations must avoid side-channel attacks by, for example,
      being constant-time.</t>
     
    </section>

    <section title="Acknowledgements">

      <t>Thanks to Yoav Nir for suggesting re-use of ECDSA cipher
      suites with EdDSA, to reduce the cartesian product cipher suite
      explosion.  Thanks to Klaus Hartke and Nicolas Williams for
      numerous fixes to the document.  Other people who contributed
      include Ilari Liusvaara and Martin Thomson.</t>

    </section>

  </middle>

  <back>

    <references title="Normative References">

      &rfc2119;
      &rfc4492;
      &rfc5246;
      &rfc6347;
      &eddsaed25519;
      
    </references>

    <references title="Informative References">

      <reference anchor="IANA-TLS" target="http://www.iana.org/assignments/tls-parameters/tls-parameters.xml">
        <front>
          <title>Transport Layer Security (TLS) Parameters</title>
          <author>
            <organization>Internet Assigned Numbers Authority</organization>
          </author>
          <date month="" year=""/>
        </front>
      </reference>

    </references>

  </back>
</rfc>