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Versions: (draft-nir-tls-rfc4492bis) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17

TLS Working Group                                                 Y. Nir
Internet-Draft                                               Check Point
Obsoletes: 4492 (if approved)                               S. Josefsson
Intended status: Standards Track                                  SJD AB
Expires: November 6, 2017                            M. Pegourie-Gonnard
                                                  Independent / PolarSSL
                                                             May 5, 2017


  Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer
                Security (TLS) Versions 1.2 and Earlier
                      draft-ietf-tls-rfc4492bis-17

Abstract

   This document describes key exchange algorithms based on Elliptic
   Curve Cryptography (ECC) for the Transport Layer Security (TLS)
   protocol.  In particular, it specifies the use of Ephemeral Elliptic
   Curve Diffie-Hellman (ECDHE) key agreement in a TLS handshake and the
   use of Elliptic Curve Digital Signature Algorithm (ECDSA) and Edwards
   Digital Signature Algorithm (EdDSA) as authentication mechanisms.

   This document obsoletes and replaces RFC 4492.

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 http://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 November 6, 2017.

Copyright Notice

   Copyright (c) 2017 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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   (http://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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   3
   2.  Key Exchange Algorithm  . . . . . . . . . . . . . . . . . . .   3
     2.1.  ECDHE_ECDSA . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  ECDHE_RSA . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  ECDH_anon . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.4.  Algorithms in Certificate Chains  . . . . . . . . . . . .   6
   3.  Client Authentication . . . . . . . . . . . . . . . . . . . .   6
     3.1.  ECDSA_sign  . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  TLS Extensions for ECC  . . . . . . . . . . . . . . . . . . .   7
   5.  Data Structures and Computations  . . . . . . . . . . . . . .   8
     5.1.  Client Hello Extensions . . . . . . . . . . . . . . . . .   8
       5.1.1.  Supported Elliptic Curves Extension . . . . . . . . .  10
       5.1.2.  Supported Point Formats Extension . . . . . . . . . .  11
       5.1.3.  The signature_algorithms Extension and EdDSA  . . . .  12
     5.2.  Server Hello Extension  . . . . . . . . . . . . . . . . .  12
     5.3.  Server Certificate  . . . . . . . . . . . . . . . . . . .  13
     5.4.  Server Key Exchange . . . . . . . . . . . . . . . . . . .  14
       5.4.1.  Uncompressed Point Format for NIST curves . . . . . .  18
     5.5.  Certificate Request . . . . . . . . . . . . . . . . . . .  18
     5.6.  Client Certificate  . . . . . . . . . . . . . . . . . . .  19
     5.7.  Client Key Exchange . . . . . . . . . . . . . . . . . . .  20
     5.8.  Certificate Verify  . . . . . . . . . . . . . . . . . . .  21
     5.9.  Elliptic Curve Certificates . . . . . . . . . . . . . . .  23
     5.10. ECDH, ECDSA, and RSA Computations . . . . . . . . . . . .  23
     5.11. Public Key Validation . . . . . . . . . . . . . . . . . .  24
   6.  Cipher Suites . . . . . . . . . . . . . . . . . . . . . . . .  24
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  25
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  26
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  27
   11. Version History for This Draft  . . . . . . . . . . . . . . .  28
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  28
     12.2.  Informative References . . . . . . . . . . . . . . . . .  30
   Appendix A.  Equivalent Curves (Informative)  . . . . . . . . . .  30
   Appendix B.  Differences from RFC 4492  . . . . . . . . . . . . .  31
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32



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1.  Introduction

   This document describes additions to TLS to support ECC, applicable
   to TLS versions 1.0 [RFC2246], 1.1 [RFC4346], and 1.2 [RFC5246].  The
   use of ECC in TLS 1.3 is defined in [I-D.ietf-tls-tls13], and is
   explicitly out of scope for this document.  In particular, this
   document defines:

   o  the use of the ECDHE key agreement scheme with ephemeral keys to
      establish the TLS premaster secret, and
   o  the use of ECDSA and EdDSA signatures for authentication of TLS
      peers.

   The remainder of this document is organized as follows.  Section 2
   provides an overview of ECC-based key exchange algorithms for TLS.
   Section 3 describes the use of ECC certificates for client
   authentication.  TLS extensions that allow a client to negotiate the
   use of specific curves and point formats are presented in Section 4.
   Section 5 specifies various data structures needed for an ECC-based
   handshake, their encoding in TLS messages, and the processing of
   those messages.  Section 6 defines ECC-based cipher suites and
   identifies a small subset of these as recommended for all
   implementations of this specification.  Section 8 discusses security
   considerations.  Section 9 describes IANA considerations for the name
   spaces created by this document's predecessor.  Section 10 gives
   acknowledgements.  Appendix B provides differences from [RFC4492],
   the document that this one replaces.

   Implementation of this specification requires familiarity with TLS,
   TLS extensions [RFC4366], and ECC.

1.1.  Conventions Used in This Document

   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 [RFC2119].

2.  Key Exchange Algorithm

   This document defines three new ECC-based key exchange algorithms for
   TLS.  All of them use Ephemeral ECDH (ECDHE) to compute the TLS
   premaster secret, and they differ only in the mechanism (if any) used
   to authenticate them.  The derivation of the TLS master secret from
   the premaster secret and the subsequent generation of bulk
   encryption/MAC keys and initialization vectors is independent of the
   key exchange algorithm and not impacted by the introduction of ECC.





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   Table 1 summarizes the new key exchange algorithms.  All of these key
   exchange algorithms provide forward secrecy if and only if fresh
   ephemeral keys are generated and used, and also destroyed after use.

     +-------------+------------------------------------------------+
     | Algorithm   | Description                                    |
     +-------------+------------------------------------------------+
     | ECDHE_ECDSA | Ephemeral ECDH with ECDSA or EdDSA signatures. |
     | ECDHE_RSA   | Ephemeral ECDH with RSA signatures.            |
     | ECDH_anon   | Anonymous ephemeral ECDH, no signatures.       |
     +-------------+------------------------------------------------+

                   Table 1: ECC Key Exchange Algorithms

   These key exchanges are analogous to DHE_DSS, DHE_RSA, and DH_anon,
   respectively.

   With ECDHE_RSA, a server can reuse its existing RSA certificate and
   easily comply with a constrained client's elliptic curve preferences
   (see Section 4).  However, the computational cost incurred by a
   server is higher for ECDHE_RSA than for the traditional RSA key
   exchange, which does not provide forward secrecy.

   The anonymous key exchange algorithm does not provide authentication
   of the server or the client.  Like other anonymous TLS key exchanges,
   it is subject to man-in-the-middle attacks.  Applications using TLS
   with this algorithm SHOULD provide authentication by other means.
























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          Client                                        Server
          ------                                        ------
          ClientHello          -------->
                                                   ServerHello
                                                  Certificate*
                                            ServerKeyExchange*
                                          CertificateRequest*+
                               <--------       ServerHelloDone
          Certificate*+
          ClientKeyExchange
          CertificateVerify*+
          [ChangeCipherSpec]
          Finished             -------->
                                            [ChangeCipherSpec]
                               <--------              Finished
          Application Data     <------->      Application Data
               * message is not sent under some conditions
               + message is not sent unless client authentication
                 is desired

   Figure 1: Message flow in a full TLS 1.2 handshake

   Figure 1 shows all messages involved in the TLS key establishment
   protocol (aka full handshake).  The addition of ECC has direct impact
   only on the ClientHello, the ServerHello, the server's Certificate
   message, the ServerKeyExchange, the ClientKeyExchange, the
   CertificateRequest, the client's Certificate message, and the
   CertificateVerify.  Next, we describe the ECC key exchange algorithm
   in greater detail in terms of the content and processing of these
   messages.  For ease of exposition, we defer discussion of client
   authentication and associated messages (identified with a + in
   Figure 1) until Section 3 and of the optional ECC-specific extensions
   (which impact the Hello messages) until Section 4.

2.1.  ECDHE_ECDSA

   In ECDHE_ECDSA, the server's certificate MUST contain an ECDSA- or
   EdDSA-capable public key.

   The server sends its ephemeral ECDH public key and a specification of
   the corresponding curve in the ServerKeyExchange message.  These
   parameters MUST be signed with ECDSA or EdDSA using the private key
   corresponding to the public key in the server's Certificate.

   The client generates an ECDH key pair on the same curve as the
   server's ephemeral ECDH key and sends its public key in the
   ClientKeyExchange message.




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   Both client and server perform an ECDH operation Section 5.10 and use
   the resultant shared secret as the premaster secret.

2.2.  ECDHE_RSA

   This key exchange algorithm is the same as ECDHE_ECDSA except that
   the server's certificate MUST contain an RSA public key authorized
   for signing, and that the signature in the ServerKeyExchange message
   must be computed with the corresponding RSA private key.

2.3.  ECDH_anon

   NOTE: Despite the name beginning with "ECDH_" (no E), the key used in
   ECDH_anon is ephemeral just like the key in ECDHE_RSA and
   ECDHE_ECDSA.  The naming follows the example of DH_anon, where the
   key is also ephemeral but the name does not reflect it.

   In ECDH_anon, the server's Certificate, the CertificateRequest, the
   client's Certificate, and the CertificateVerify messages MUST NOT be
   sent.

   The server MUST send an ephemeral ECDH public key and a specification
   of the corresponding curve in the ServerKeyExchange message.  These
   parameters MUST NOT be signed.

   The client generates an ECDH key pair on the same curve as the
   server's ephemeral ECDH key and sends its public key in the
   ClientKeyExchange message.

   Both client and server perform an ECDH operation and use the
   resultant shared secret as the premaster secret.  All ECDH
   calculations are performed as specified in Section 5.10.

2.4.  Algorithms in Certificate Chains

   This specification does not impose restrictions on signature schemes
   used anywhere in the certificate chain.  The previous version of this
   document required the signatures to match, but this restriction,
   originating in previous TLS versions is lifted here as it had been in
   RFC 5246.

3.  Client Authentication

   This document defines a client authentication mechanism, named after
   the type of client certificate involved: ECDSA_sign.  The ECDSA_sign
   mechanism is usable with any of the non-anonymous ECC key exchange
   algorithms described in Section 2 as well as other non-anonymous
   (non-ECC) key exchange algorithms defined in TLS.



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   Note that client certificates with EdDSA public keys also use this
   mechanism.

   The server can request ECC-based client authentication by including
   this certificate type in its CertificateRequest message.  The client
   must check if it possesses a certificate appropriate for the method
   suggested by the server and is willing to use it for authentication.

   If these conditions are not met, the client SHOULD send a client
   Certificate message containing no certificates.  In this case, the
   ClientKeyExchange MUST be sent as described in Section 2, and the
   CertificateVerify MUST NOT be sent.  If the server requires client
   authentication, it may respond with a fatal handshake failure alert.

   If the client has an appropriate certificate and is willing to use it
   for authentication, it must send that certificate in the client's
   Certificate message (as per Section 5.6) and prove possession of the
   private key corresponding to the certified key.  The process of
   determining an appropriate certificate and proving possession is
   different for each authentication mechanism and described below.

   NOTE: It is permissible for a server to request (and the client to
   send) a client certificate of a different type than the server
   certificate.

3.1.  ECDSA_sign

   To use this authentication mechanism, the client MUST possess a
   certificate containing an ECDSA- or EdDSA-capable public key.

   The client proves possession of the private key corresponding to the
   certified key by including a signature in the CertificateVerify
   message as described in Section 5.8.

4.  TLS Extensions for ECC

   Two TLS extensions are defined in this specification: (i) the
   Supported Elliptic Curves Extension, and (ii) the Supported Point
   Formats Extension.  These allow negotiating the use of specific
   curves and point formats (e.g., compressed vs. uncompressed,
   respectively) during a handshake starting a new session.  These
   extensions are especially relevant for constrained clients that may
   only support a limited number of curves or point formats.  They
   follow the general approach outlined in [RFC4366]; message details
   are specified in Section 5.  The client enumerates the curves it
   supports and the point formats it can parse by including the
   appropriate extensions in its ClientHello message.  The server




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   similarly enumerates the point formats it can parse by including an
   extension in its ServerHello message.

   A TLS client that proposes ECC cipher suites in its ClientHello
   message SHOULD include these extensions.  Servers implementing ECC
   cipher suites MUST support these extensions, and when a client uses
   these extensions, servers MUST NOT negotiate the use of an ECC cipher
   suite unless they can complete the handshake while respecting the
   choice of curves specified by the client.  This eliminates the
   possibility that a negotiated ECC handshake will be subsequently
   aborted due to a client's inability to deal with the server's EC key.

   The client MUST NOT include these extensions in the ClientHello
   message if it does not propose any ECC cipher suites.  A client that
   proposes ECC cipher suites may choose not to include these
   extensions.  In this case, the server is free to choose any one of
   the elliptic curves or point formats listed in Section 5.  That
   section also describes the structure and processing of these
   extensions in greater detail.

   In the case of session resumption, the server simply ignores the
   Supported Elliptic Curves Extension and the Supported Point Formats
   Extension appearing in the current ClientHello message.  These
   extensions only play a role during handshakes negotiating a new
   session.

5.  Data Structures and Computations

   This section specifies the data structures and computations used by
   ECC-based key mechanisms specified in the previous three sections.
   The presentation language used here is the same as that used in TLS.
   Since this specification extends TLS, these descriptions should be
   merged with those in the TLS specification and any others that extend
   TLS.  This means that enum types may not specify all possible values,
   and structures with multiple formats chosen with a select() clause
   may not indicate all possible cases.

5.1.  Client Hello Extensions

   This section specifies two TLS extensions that can be included with
   the ClientHello message as described in [RFC4366], the Supported
   Elliptic Curves Extension and the Supported Point Formats Extension.

   When these extensions are sent:

   The extensions SHOULD be sent along with any ClientHello message that
   proposes ECC cipher suites.




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   Meaning of these extensions:

   These extensions allow a client to enumerate the elliptic curves it
   supports and/or the point formats it can parse.

   Structure of these extensions:

   The general structure of TLS extensions is described in [RFC4366],
   and this specification adds two types to ExtensionType.

      enum {
          elliptic_curves(10),
          ec_point_formats(11)
      } ExtensionType;

   o  elliptic_curves (Supported Elliptic Curves Extension): Indicates
      the set of elliptic curves supported by the client.  For this
      extension, the opaque extension_data field contains
      NamedCurveList.  See Section 5.1.1 for details.
   o  ec_point_formats (Supported Point Formats Extension): Indicates
      the set of point formats that the client can parse.  For this
      extension, the opaque extension_data field contains
      ECPointFormatList.  See Section 5.1.2 for details.

   Actions of the sender:

   A client that proposes ECC cipher suites in its ClientHello message
   appends these extensions (along with any others), enumerating the
   curves it supports and the point formats it can parse.  Clients
   SHOULD send both the Supported Elliptic Curves Extension and the
   Supported Point Formats Extension.  If the Supported Point Formats
   Extension is indeed sent, it MUST contain the value 0 (uncompressed)
   as one of the items in the list of point formats.

   Actions of the receiver:

   A server that receives a ClientHello containing one or both of these
   extensions MUST use the client's enumerated capabilities to guide its
   selection of an appropriate cipher suite.  One of the proposed ECC
   cipher suites must be negotiated only if the server can successfully
   complete the handshake while using the curves and point formats
   supported by the client (cf.  Section 5.3 and Section 5.4).

   NOTE: A server participating in an ECDHE_ECDSA key exchange may use
   different curves for the ECDSA or EdDSA key in its certificate, and
   for the ephemeral ECDH key in the ServerKeyExchange message.  The
   server MUST consider the extensions in both cases.




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   If a server does not understand the Supported Elliptic Curves
   Extension, does not understand the Supported Point Formats Extension,
   or is unable to complete the ECC handshake while restricting itself
   to the enumerated curves and point formats, it MUST NOT negotiate the
   use of an ECC cipher suite.  Depending on what other cipher suites
   are proposed by the client and supported by the server, this may
   result in a fatal handshake failure alert due to the lack of common
   cipher suites.

5.1.1.  Supported Elliptic Curves Extension

   RFC 4492 defined 25 different curves in the NamedCurve registry (now
   renamed the "Supported Groups" registry, although the enumeration
   below is still named NamedCurve) for use in TLS.  Only three have
   seen much use.  This specification is deprecating the rest (with
   numbers 1-22).  This specification also deprecates the explicit
   curves with identifiers 0xFF01 and 0xFF02.  It also adds the new
   curves defined in [RFC7748].  The end result is as follows:

           enum {
               deprecated(1..22),
               secp256r1 (23), secp384r1 (24), secp521r1 (25),
               x25519(29), x448(30),
               reserved (0xFE00..0xFEFF),
               deprecated(0xFF01..0xFF02),
               (0xFFFF)
           } NamedCurve;

   Note that other specifications have since added other values to this
   enumeration.  Some of those values are not curves at all, but finite
   field groups.  See [RFC7919].

   secp256r1, etc: Indicates support of the corresponding named curve or
   groups.  The named curves secp256r1, secp384r1, and secp521r1 are
   specified in SEC 2 [SECG-SEC2].  These curves are also recommended in
   ANSI X9.62 [ANSI.X9-62.2005] and FIPS 186-4 [FIPS.186-4].  The rest
   of this document refers to these three curves as the "NIST curves"
   because they were originally standardized by the National Institute
   of Standards and Technology.  The curves x25519 and x448 are defined
   in [RFC7748].  Values 0xFE00 through 0xFEFF are reserved for private
   use.

   The predecessor of this document also supported explicitly defined
   prime and char2 curves, but these are deprecated by this
   specification.

   The NamedCurve name space is maintained by IANA.  See Section 9 for
   information on how new value assignments are added.



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           struct {
               NamedCurve named_curve_list<2..2^16-1>
           } NamedCurveList;

   Items in named_curve_list are ordered according to the client's
   preferences (favorite choice first).

   As an example, a client that only supports secp256r1 (aka NIST P-256;
   value 23 = 0x0017) and secp384r1 (aka NIST P-384; value 24 = 0x0018)
   and prefers to use secp256r1 would include a TLS extension consisting
   of the following octets.  Note that the first two octets indicate the
   extension type (Supported Elliptic Curves Extension):

           00 0A 00 06 00 04 00 17 00 18

5.1.2.  Supported Point Formats Extension

           enum {
               uncompressed (0),
               deprecated (1..2),
               reserved (248..255)
           } ECPointFormat;
           struct {
               ECPointFormat ec_point_format_list<1..2^8-1>
           } ECPointFormatList;

   Three point formats were included in the definition of ECPointFormat
   above.  This specification deprecates all but the uncompressed point
   format.  Implementations of this document MUST support the
   uncompressed format for all of their supported curves, and MUST NOT
   support other formats for curves defined in this specification.  For
   backwards compatibility purposes, the point format list extension MAY
   still be included, and contain exactly one value: the uncompressed
   point format (0).  RFC 4492 specified that if this extension is
   missing, it means that only the uncompressed point format is
   supported, so interoperability with implementations that support the
   uncompressed format should work with or without the extension.

   If the client sends the extension and the extension does not contain
   the uncompressed point format, and the client has used the Supported
   Groups extension to indicate support for any of the curves defined in
   this specification then the server MUST abort the handshake and
   return an illegal_parameter alert.

   The ECPointFormat name space is maintained by IANA.  See Section 9
   for information on how new value assignments are added.





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   A client compliant with this specification that supports no other
   curves MUST send the following octets; note that the first two octets
   indicate the extension type (Supported Point Formats Extension):

           00 0B 00 02 01 00

5.1.3.  The signature_algorithms Extension and EdDSA

   The signature_algorithms extension, defined in section 7.4.1.4.1 of
   [RFC5246], advertises the combinations of signature algorithm and
   hash function that the client supports.  The pure (non pre-hashed)
   forms of EdDSA do not hash the data before signing it.  For this
   reason it does not make sense to combine them with a signature
   algorithm in the extension.

   For bits-on-the-wire compatibility with TLS 1.3, we define a new
   dummy value in the HashAlgorithm registry which we will call
   "Intrinsic" (value TBD5) meaning that hashing is intrinsic to the
   signature algorithm.

   To represent ed25519 and ed448 in the signature_algorithms extension,
   the value shall be (TBD5,TBD3) and (TBD5,TBD4) respectively.

5.2.  Server Hello Extension

   This section specifies a TLS extension that can be included with the
   ServerHello message as described in [RFC4366], the Supported Point
   Formats Extension.

   When this extension is sent:

   The Supported Point Formats Extension is included in a ServerHello
   message in response to a ClientHello message containing the Supported
   Point Formats Extension when negotiating an ECC cipher suite.

   Meaning of this extension:

   This extension allows a server to enumerate the point formats it can
   parse (for the curve that will appear in its ServerKeyExchange
   message when using the ECDHE_ECDSA, ECDHE_RSA, or ECDH_anon key
   exchange algorithm.

   Structure of this extension:

   The server's Supported Point Formats Extension has the same structure
   as the client's Supported Point Formats Extension (see
   Section 5.1.2).  Items in ec_point_format_list here are ordered
   according to the server's preference (favorite choice first).  Note



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   that the server MAY include items that were not found in the client's
   list.  However, without extensions this specification allows exactly
   one point format, so there is not really any opportunity for
   mismatches.

   Actions of the sender:

   A server that selects an ECC cipher suite in response to a
   ClientHello message including a Supported Point Formats Extension
   appends this extension (along with others) to its ServerHello
   message, enumerating the point formats it can parse.  The Supported
   Point Formats Extension, when used, MUST contain the value 0
   (uncompressed) as one of the items in the list of point formats.

   Actions of the receiver:

   A client that receives a ServerHello message containing a Supported
   Point Formats Extension MUST respect the server's choice of point
   formats during the handshake (cf.  Section 5.6 and Section 5.7).  If
   no Supported Point Formats Extension is received with the
   ServerHello, this is equivalent to an extension allowing only the
   uncompressed point format.

5.3.  Server Certificate

   When this message is sent:

   This message is sent in all non-anonymous ECC-based key exchange
   algorithms.

   Meaning of this message:

   This message is used to authentically convey the server's static
   public key to the client.  The following table shows the server
   certificate type appropriate for each key exchange algorithm.  ECC
   public keys MUST be encoded in certificates as described in
   Section 5.9.

   NOTE: The server's Certificate message is capable of carrying a chain
   of certificates.  The restrictions mentioned in Table 3 apply only to
   the server's certificate (first in the chain).










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   +-------------+-----------------------------------------------------+
   | Algorithm   | Server Certificate Type                             |
   +-------------+-----------------------------------------------------+
   | ECDHE_ECDSA | Certificate MUST contain an ECDSA- or EdDSA-capable |
   |             | public key.                                         |
   | ECDHE_RSA   | Certificate MUST contain an RSA public key.         |
   +-------------+-----------------------------------------------------+

                     Table 2: Server Certificate Types

   Structure of this message:

   Identical to the TLS Certificate format.

   Actions of the sender:

   The server constructs an appropriate certificate chain and conveys it
   to the client in the Certificate message.  If the client has used a
   Supported Elliptic Curves Extension, the public key in the server's
   certificate MUST respect the client's choice of elliptic curves.  A
   server that cannot satisfy this requirement MUST NOT choose an ECC
   cipher suite in its ServerHello message.)

   Actions of the receiver:

   The client validates the certificate chain, extracts the server's
   public key, and checks that the key type is appropriate for the
   negotiated key exchange algorithm.  (A possible reason for a fatal
   handshake failure is that the client's capabilities for handling
   elliptic curves and point formats are exceeded; cf. Section 5.1.)

5.4.  Server Key Exchange

   When this message is sent:

   This message is sent when using the ECDHE_ECDSA, ECDHE_RSA, and
   ECDH_anon key exchange algorithms.

   Meaning of this message:

   This message is used to convey the server's ephemeral ECDH public key
   (and the corresponding elliptic curve domain parameters) to the
   client.

   The ECCCurveType enum used to have values for explicit prime and for
   explicit char2 curves.  Those values are now deprecated, so only one
   value remains:




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   Structure of this message:

           enum {
               deprecated (1..2),
               named_curve (3),
               reserved(248..255)
           } ECCurveType;

   The value named_curve indicates that a named curve is used.  This
   option is now the only remaining format.

   Values 248 through 255 are reserved for private use.

   The ECCurveType name space is maintained by IANA.  See Section 9 for
   information on how new value assignments are added.

   RFC 4492 had a specification for an ECCurve structure and an
   ECBasisType structure.  Both of these are omitted now because they
   were only used with the now deprecated explicit curves.

           struct {
               opaque point <1..2^8-1>;
           } ECPoint;

   point: This is the byte string representation of an elliptic curve
   point following the conversion routine in Section 4.3.6 of
   [ANSI.X9-62.2005].  This byte string may represent an elliptic curve
   point in uncompressed, compressed, or hybrid format, but this
   specification deprecates all but the uncompressed format.  For the
   NIST curves, the format is repeated in Section 5.4.1 for convenience.
   For the X25519 and X448 curves, the only valid representation is the
   one specified in [RFC7748] - a 32- or 56-octet representation of the
   u value of the point.  This structure MUST NOT be used with Ed25519
   and Ed448 public keys.

           struct {
               ECCurveType    curve_type;
               select (curve_type) {
                   case named_curve:
                       NamedCurve namedcurve;
               };
           } ECParameters;

   curve_type: This identifies the type of the elliptic curve domain
   parameters.

   namedCurve: Specifies a recommended set of elliptic curve domain
   parameters.  All those values of NamedCurve are allowed that refer to



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   a curve capable of Diffie-Hellman.  With the deprecation of the
   explicit curves, this now includes all of the NamedCurve values.

           struct {
               ECParameters    curve_params;
               ECPoint         public;
           } ServerECDHParams;

   curve_params: Specifies the elliptic curve domain parameters
   associated with the ECDH public key.

   public: The ephemeral ECDH public key.

   The ServerKeyExchange message is extended as follows.

           enum {
               ec_diffie_hellman
           } KeyExchangeAlgorithm;

   o  ec_diffie_hellman: Indicates the ServerKeyExchange message
      contains an ECDH public key.

      select (KeyExchangeAlgorithm) {
          case ec_diffie_hellman:
              ServerECDHParams    params;
              Signature           signed_params;
      } ServerKeyExchange;

   o  params: Specifies the ECDH public key and associated domain
      parameters.
   o  signed_params: A hash of the params, with the signature
      appropriate to that hash applied.  The private key corresponding
      to the certified public key in the server's Certificate message is
      used for signing.

















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        enum {
            ecdsa(3),
            ed25519(TBD3)
            ed448(TBD4)
        } SignatureAlgorithm;
        select (SignatureAlgorithm) {
           case ecdsa:
                digitally-signed struct {
                    opaque sha_hash[sha_size];
                };
           case ed25519,ed448:
                digitally-signed struct {
                    opaque rawdata[rawdata_size];
                };
        } Signature;
      ServerKeyExchange.signed_params.sha_hash
          SHA(ClientHello.random + ServerHello.random +
                                 ServerKeyExchange.params);
      ServerKeyExchange.signed_params.rawdata
          ClientHello.random + ServerHello.random +
                                 ServerKeyExchange.params;

   NOTE: SignatureAlgorithm is "rsa" for the ECDHE_RSA key exchange
   algorithm and "anonymous" for ECDH_anon.  These cases are defined in
   TLS.  SignatureAlgorithm is "ecdsa" or "eddsa" for ECDHE_ECDSA.
   ECDSA signatures are generated and verified as described in
   Section 5.10, and SHA in the above template for sha_hash accordingly
   may denote a hash algorithm other than SHA-1.  As per ANSI X9.62, an
   ECDSA signature consists of a pair of integers, r and s.  The
   digitally-signed element is encoded as an opaque vector <0..2^16-1>,
   the contents of which are the DER encoding corresponding to the
   following ASN.1 notation.

              Ecdsa-Sig-Value ::= SEQUENCE {
                  r       INTEGER,
                  s       INTEGER
              }

   EdDSA signatures in both the protocol and in certificates that
   conform to [PKIX-EdDSA] are generated and verified according to
   [RFC8032].  The digitally-signed element is encoded as an opaque
   vector<0..2^16-1>, the contents of which is the octet string output
   of the EdDSA signing algorithm.

   Actions of the sender:

   The server selects elliptic curve domain parameters and an ephemeral
   ECDH public key corresponding to these parameters according to the



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   ECKAS-DH1 scheme from IEEE 1363 [IEEE.P1363.1998].  It conveys this
   information to the client in the ServerKeyExchange message using the
   format defined above.

   Actions of the receiver:

   The client verifies the signature (when present) and retrieves the
   server's elliptic curve domain parameters and ephemeral ECDH public
   key from the ServerKeyExchange message.  (A possible reason for a
   fatal handshake failure is that the client's capabilities for
   handling elliptic curves and point formats are exceeded; cf.
   Section 5.1.)

5.4.1.  Uncompressed Point Format for NIST curves

   The following represents the wire format for representing ECPoint in
   ServerKeyExchange records.  The first octet of the representation
   indicates the form, which may be compressed, uncompressed, or hybrid.
   This specification supports only the uncompressed format for these
   curves.  This is followed by the binary representation of the X value
   in "big-endian" or "network" format, followed by the binary
   representation of the Y value in "big-endian" or "network" format.
   There are no internal length markers, so each number representation
   occupies as many octets as implied by the curve parameters.  For
   P-256 this means that each of X and Y use 32 octets, padded on the
   left by zeros if necessary.  For P-384 they take 48 octets each, and
   for P-521 they take 66 octets each.

   Here's a more formal representation:

             enum {
                 uncompressed(4),
                 (255)
               } PointConversionForm;

             struct {
                 PointConversionForm  form;
                 opaque               X[coordinate_length];
                 opaque               Y[coordinate_length];
             } UncompressedPointRepresentation;

5.5.  Certificate Request

   When this message is sent:

   This message is sent when requesting client authentication.

   Meaning of this message:



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   The server uses this message to suggest acceptable client
   authentication methods.

   Structure of this message:

   The TLS CertificateRequest message is extended as follows.

           enum {
               ecdsa_sign(64),
               deprecated1(65),  /* was rsa_fixed_ecdh */
               deprecated2(66),  /* was ecdsa_fixed_ecdh */
               (255)
           } ClientCertificateType;

   o  ecdsa_sign: Indicates that the server would like to use the
      corresponding client authentication method specified in Section 3.

   Note that RFC 4492 also defined RSA and ECDSA certificates that
   included a fixed ECDH public key.  These mechanisms saw very little
   implementation so this specification is deprecating them.

   Actions of the sender:

   The server decides which client authentication methods it would like
   to use, and conveys this information to the client using the format
   defined above.

   Actions of the receiver:

   The client determines whether it has a suitable certificate for use
   with any of the requested methods and whether to proceed with client
   authentication.

5.6.  Client Certificate

   When this message is sent:

   This message is sent in response to a CertificateRequest when a
   client has a suitable certificate and has decided to proceed with
   client authentication.  (Note that if the server has used a Supported
   Point Formats Extension, a certificate can only be considered
   suitable for use with the ECDSA_sign authentication method if the
   public key point specified in it is uncompressed, as that is the only
   point format still supported.

   Meaning of this message:





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   This message is used to authentically convey the client's static
   public key to the server.  The following table summarizes what client
   certificate types are appropriate for the ECC-based client
   authentication mechanisms described in Section 3.  ECC public keys
   must be encoded in certificates as described in Section 5.9.

   NOTE: The client's Certificate message is capable of carrying a chain
   of certificates.  The restrictions mentioned in Table 4 apply only to
   the client's certificate (first in the chain).

   The certificate MUST contain an ECDSA- or EdDSA-capable public key.

   Structure of this message:

   Identical to the TLS client Certificate format.

   Actions of the sender:

   The client constructs an appropriate certificate chain, and conveys
   it to the server in the Certificate message.

   Actions of the receiver:

   The TLS server validates the certificate chain, extracts the client's
   public key, and checks that the key type is appropriate for the
   client authentication method.

5.7.  Client Key Exchange

   When this message is sent:

   This message is sent in all key exchange algorithms.  It contains the
   client's ephemeral ECDH public key.

   Meaning of the message:

   This message is used to convey ephemeral data relating to the key
   exchange belonging to the client (such as its ephemeral ECDH public
   key).

   Structure of this message:

   The TLS ClientKeyExchange message is extended as follows.

           enum {
               implicit,
               explicit
           } PublicValueEncoding;



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   o  implicit, explicit: For ECC cipher suites, this indicates whether
      the client's ECDH public key is in the client's certificate
      ("implicit") or is provided, as an ephemeral ECDH public key, in
      the ClientKeyExchange message ("explicit").  The implicit encoding
      is deprecated and is retained here for backward compatibility
      only.

           struct {
               ECPoint ecdh_Yc;
           } ClientECDiffieHellmanPublic;

   ecdh_Yc: Contains the client's ephemeral ECDH public key as a byte
   string ECPoint.point, which may represent an elliptic curve point in
   uncompressed format.

           struct {
               select (KeyExchangeAlgorithm) {
                   case ec_diffie_hellman: ClientECDiffieHellmanPublic;
               } exchange_keys;
           } ClientKeyExchange;

   Actions of the sender:

   The client selects an ephemeral ECDH public key corresponding to the
   parameters it received from the server.  The format is the same as in
   Section 5.4.

   Actions of the receiver:

   The server retrieves the client's ephemeral ECDH public key from the
   ClientKeyExchange message and checks that it is on the same elliptic
   curve as the server's ECDH key.

5.8.  Certificate Verify

   When this message is sent:

   This message is sent when the client sends a client certificate
   containing a public key usable for digital signatures.

   Meaning of the message:

   This message contains a signature that proves possession of the
   private key corresponding to the public key in the client's
   Certificate message.

   Structure of this message:




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   The TLS CertificateVerify message and the underlying Signature type
   are defined in the TLS base specifications, and the latter is
   extended here in Section 5.4.  For the ecdsa and eddsa cases, the
   signature field in the CertificateVerify message contains an ECDSA or
   EdDSA (respectively) signature computed over handshake messages
   exchanged so far, exactly similar to CertificateVerify with other
   signing algorithms:

           CertificateVerify.signature.sha_hash
               SHA(handshake_messages);
           CertificateVerify.signature.rawdata
               handshake_messages;

   ECDSA signatures are computed as described in Section 5.10, and SHA
   in the above template for sha_hash accordingly may denote a hash
   algorithm other than SHA-1.  As per ANSI X9.62, an ECDSA signature
   consists of a pair of integers, r and s.  The digitally-signed
   element is encoded as an opaque vector <0..2^16-1>, the contents of
   which are the DER encoding [CCITT.X690] corresponding to the
   following ASN.1 notation [CCITT.X680].

           Ecdsa-Sig-Value ::= SEQUENCE {
               r       INTEGER,
               s       INTEGER
           }

   EdDSA signatures are generated and verified according to [RFC8032].
   The digitally-signed element is encoded as an opaque
   vector<0..2^16-1>, the contents of which is the octet string output
   of the EdDSA signing algorithm.

   Actions of the sender:

   The client computes its signature over all handshake messages sent or
   received starting at client hello and up to but not including this
   message.  It uses the private key corresponding to its certified
   public key to compute the signature, which is conveyed in the format
   defined above.

   Actions of the receiver:

   The server extracts the client's signature from the CertificateVerify
   message, and verifies the signature using the public key it received
   in the client's Certificate message.







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5.9.  Elliptic Curve Certificates

   X.509 certificates containing ECC public keys or signed using ECDSA
   MUST comply with [RFC3279] or another RFC that replaces or extends
   it.  X.509 certificates containing ECC public keys or signed using
   EdDSA MUST comply with [PKIX-EdDSA].  Clients SHOULD use the elliptic
   curve domain parameters recommended in ANSI X9.62, FIPS 186-4, and
   SEC 2 [SECG-SEC2] or in [RFC8032].

   EdDSA keys using the Ed25519 algorithm MUST use the ed25519 signature
   algorithm, and Ed448 keys MUST use the ed448 signature algorithm.
   This document does not define use of Ed25519ph and Ed448ph keys with
   TLS.  Ed25519, Ed25519ph, Ed448, and Ed448ph keys MUST NOT be used
   with ECDSA.

5.10.  ECDH, ECDSA, and RSA Computations

   All ECDH calculations for the NIST curves (including parameter and
   key generation as well as the shared secret calculation) are
   performed according to [IEEE.P1363.1998] using the ECKAS-DH1 scheme
   with the identity map as key derivation function (KDF), so that the
   premaster secret is the x-coordinate of the ECDH shared secret
   elliptic curve point represented as an octet string.  Note that this
   octet string (Z in IEEE 1363 terminology) as output by FE2OSP, the
   Field Element to Octet String Conversion Primitive, has constant
   length for any given field; leading zeros found in this octet string
   MUST NOT be truncated.

   (Note that this use of the identity KDF is a technicality.  The
   complete picture is that ECDH is employed with a non-trivial KDF
   because TLS does not directly use the premaster secret for anything
   other than for computing the master secret.  In TLS 1.0 and 1.1, this
   means that the MD5- and SHA-1-based TLS PRF serves as a KDF; in TLS
   1.2 the KDF is determined by ciphersuite; it is conceivable that
   future TLS versions or new TLS extensions introduced in the future
   may vary this computation.)

   An ECDHE key exchange using X25519 (curve x25519) goes as follows:
   Each party picks a secret key d uniformly at random and computes the
   corresponding public key x = X25519(d, G).  Parties exchange their
   public keys, and compute a shared secret as x_S = X25519(d, x_peer).
   If either party obtains all-zeroes x_S, it MUST abort the handshake
   (as required by definition of X25519 and X448).  ECDHE for X448 works
   similarily, replacing X25519 with X448, and x25519 with x448.  The
   derived shared secret is used directly as the premaster secret, which
   is always exactly 32 bytes when ECDHE with X25519 is used and 56
   bytes when ECDHE with X448 is used.




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   All ECDSA computations MUST be performed according to ANSI X9.62 or
   its successors.  Data to be signed/verified is hashed, and the result
   run directly through the ECDSA algorithm with no additional hashing.
   A secure hash function such as SHA-256, SHA-384, or SHA-512 from
   [FIPS.180-4] MUST be used.

   All EdDSA computations MUST be performed according to [RFC8032] or
   its succesors.  Data to be signed/verified is run through the EdDSA
   algorithm wih no hashing (EdDSA will internally run the data through
   the PH function).  The context parameter for Ed448 MUST be set to the
   empty string.

   RFC 4492 anticipated the standardization of a mechanism for
   specifying the required hash function in the certificate, perhaps in
   the parameters field of the subjectPublicKeyInfo.  Such
   standardization never took place, and as a result, SHA-1 is used in
   TLS 1.1 and earlier (except for EdDSA, which uses identity function).
   TLS 1.2 added a SignatureAndHashAlgorithm parameter to the
   DigitallySigned struct, thus allowing agility in choosing the
   signature hash.  EdDSA signatures MUST have HashAlgorithm of TBD5
   (Intrinsic).

   All RSA signatures must be generated and verified according to
   [PKCS1] block type 1.

5.11.  Public Key Validation

   With the NIST curves, each party MUST validate the public key sent by
   its peer in the ClientKeyExchange and ServerKeyExchange messages.  A
   receiving party MUST check that the x and y parameters from the
   peer's public value satisfy the curve equation, y^2 = x^3 + ax + b
   mod p.  See section 2.3 of [Menezes] for details.  Failing to do so
   allows attackers to gain information about the private key, to the
   point that they may recover the entire private key in a few requests,
   if that key is not really ephemeral.

   With X25519 and X448, a receiving party MUST check whether the
   computed premaster secret is the all-zero value and abort the
   handshake if so, as described in section 6 of [RFC7748].

   Ed25519 and Ed448 internally do public key validation as part of
   signature verification.

6.  Cipher Suites

   The table below defines ECC cipher suites that use the key exchange
   algorithms specified in Section 2.




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       +-----------------------------------------+----------------+
       | CipherSuite                             | Identifier     |
       +-----------------------------------------+----------------+
       | TLS_ECDHE_ECDSA_WITH_NULL_SHA           | { 0xC0, 0x06 } |
       | TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA   | { 0xC0, 0x08 } |
       | TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA    | { 0xC0, 0x09 } |
       | TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA    | { 0xC0, 0x0A } |
       | TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 | { 0xC0, 0x2B } |
       | TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 | { 0xC0, 0x2C } |
       |                                         |                |
       | TLS_ECDHE_RSA_WITH_NULL_SHA             | { 0xC0, 0x10 } |
       | TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA     | { 0xC0, 0x12 } |
       | TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA      | { 0xC0, 0x13 } |
       | TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA      | { 0xC0, 0x14 } |
       | TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256   | { 0xC0, 0x2F } |
       | TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384   | { 0xC0, 0x30 } |
       |                                         |                |
       | TLS_ECDH_anon_WITH_NULL_SHA             | { 0xC0, 0x15 } |
       | TLS_ECDH_anon_WITH_3DES_EDE_CBC_SHA     | { 0xC0, 0x17 } |
       | TLS_ECDH_anon_WITH_AES_128_CBC_SHA      | { 0xC0, 0x18 } |
       | TLS_ECDH_anon_WITH_AES_256_CBC_SHA      | { 0xC0, 0x19 } |
       +-----------------------------------------+----------------+

                      Table 3: TLS ECC cipher suites

   The key exchange method, cipher, and hash algorithm for each of these
   cipher suites are easily determined by examining the name.  Ciphers
   (other than AES ciphers) and hash algorithms are defined in [RFC2246]
   and [RFC4346].  AES ciphers are defined in [RFC5246], and AES-GCM
   ciphersuites are in [RFC5289].

   Server implementations SHOULD support all of the following cipher
   suites, and client implementations SHOULD support at least one of
   them:

   o  TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
   o  TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
   o  TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
   o  TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256

7.  Implementation Status

   Both ECDHE and ECDSA with the NIST curves are widely implemented,
   supported in all major browsers and all widely used TLS libraries.
   ECDHE with Curve25519 is by now implemented in several browsers and
   several TLS libraries including OpenSSL.  Curve448 and EdDSA have
   working, interoperable implementations, but are not yet as widely
   deployed.



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8.  Security Considerations

   Security issues are discussed throughout this memo.

   For TLS handshakes using ECC cipher suites, the security
   considerations in appendices D of all three TLS base documemts apply
   accordingly.

   Security discussions specific to ECC can be found in
   [IEEE.P1363.1998] and [ANSI.X9-62.2005].  One important issue that
   implementers and users must consider is elliptic curve selection.
   Guidance on selecting an appropriate elliptic curve size is given in
   Table 1.  Security considerations specific to X25519 and X448 are
   discussed in section 7 of [RFC7748].

   Beyond elliptic curve size, the main issue is elliptic curve
   structure.  As a general principle, it is more conservative to use
   elliptic curves with as little algebraic structure as possible.
   Thus, random curves are more conservative than special curves such as
   Koblitz curves, and curves over F_p with p random are more
   conservative than curves over F_p with p of a special form, and
   curves over F_p with p random are considered more conservative than
   curves over F_2^m as there is no choice between multiple fields of
   similar size for characteristic 2.

   Another issue is the potential for catastrophic failures when a
   single elliptic curve is widely used.  In this case, an attack on the
   elliptic curve might result in the compromise of a large number of
   keys.  Again, this concern may need to be balanced against efficiency
   and interoperability improvements associated with widely-used curves.
   Substantial additional information on elliptic curve choice can be
   found in [IEEE.P1363.1998], [ANSI.X9-62.2005], and [FIPS.186-4].

   The Introduction of [RFC8032] lists the security, performance, and
   operational advantages of EdDSA signatures over ECDSA signatures
   using the NIST curves.

   All of the key exchange algorithms defined in this document provide
   forward secrecy.  Some of the deprecated key exchange algorithms do
   not.

9.  IANA Considerations

   [RFC4492], the predecessor of this document has already defined the
   IANA registries for the following:

   o  Supported Groups Section 5.1
   o  ECPointFormat Section 5.1



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   o  ECCurveType Section 5.4

   IANA is requested to prepend "TLS" to the names of the previous three
   registries.

   For each name space, this document defines the initial value
   assignments and defines a range of 256 values (NamedCurve) or eight
   values (ECPointFormat and ECCurveType) reserved for Private Use.  The
   policy for any additional assignments is "Specification Required".
   The previous version of this document required IETF review.

   NOTE: IANA, please update the registries to reflect the new policy.

   NOTE: RFC editor please delete these two notes prior to publication.

   IANA, please update these two registries to refer to this document.

   IANA is requested to assigned the value 29 to x25519, and the value
   30 to x448 in the TLS Supported Groups Registry.  This replaces the
   temporary registrations ecdh_x25519(29) and ecdh_x448(30).

   IANA is requested to assign two values from the TLS
   SignatureAlgorithm Registry with names ed25519(TBD3) and ed448(TBD4)
   with this document as reference.  To keep compatibility with TLS 1.3,
   TBD3 should be 7, and TBD4 should be 8.

   IANA is requested to assign one value from the "TLS HashAlgorithm
   Registry" with name Intrinsic(TBD5) and this document as reference.
   To keep compatibility with TLS 1.3, TBD5 should be 8 and DTLS-OK
   should be set to true (Y).

10.  Acknowledgements

   Most of the text is this document is taken from [RFC4492], the
   predecessor of this document.  The authors of that document were:

   o  Simon Blake-Wilson
   o  Nelson Bolyard
   o  Vipul Gupta
   o  Chris Hawk
   o  Bodo Moeller

   In the predecessor document, the authors acknowledged the
   contributions of Bill Anderson and Tim Dierks.

   The author would like to thank Nikos Mavrogiannopoulos, Martin
   Thomson, and Tanja Lange for contributions to this document.




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11.  Version History for This Draft

   NOTE TO RFC EDITOR: PLEASE REMOVE THIS SECTION

   Changes from draft-ietf-tls-rfc4492bis-03 to draft-nir-tls-
   rfc4492bis-05:

   o  Add support for CFRG curves and signatures work.

   Changes from draft-ietf-tls-rfc4492bis-01 to draft-nir-tls-
   rfc4492bis-03:

   o  Removed unused curves.
   o  Removed unused point formats (all but uncompressed)

   Changes from draft-nir-tls-rfc4492bis-00 and draft-ietf-tls-
   rfc4492bis-00 to draft-nir-tls-rfc4492bis-01:

   o  Merged errata
   o  Removed ECDH_RSA and ECDH_ECDSA

   Changes from RFC 4492 to draft-nir-tls-rfc4492bis-00:

   o  Added TLS 1.2 to references.
   o  Moved RFC 4492 authors to acknowledgements.
   o  Removed list of required reading for ECC.
   o  Prepended "TLS" to the names of the three registries defined in
      the IANA Considerations section.

12.  References

12.1.  Normative References

   [ANSI.X9-62.2005]
              American National Standards Institute, "Public Key
              Cryptography for the Financial Services Industry, The
              Elliptic Curve Digital Signature Algorithm (ECDSA)",
              ANSI X9.62, 2005.

   [CCITT.X680]
              International Telephone and Telegraph Consultative
              Committee, "Abstract Syntax Notation One (ASN.1):
              Specification of basic notation", CCITT Recommendation
              X.680, July 2002.







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   [CCITT.X690]
              International Telephone and Telegraph Consultative
              Committee, "ASN.1 encoding rules: Specification of basic
              encoding Rules (BER), Canonical encoding rules (CER) and
              Distinguished encoding rules (DER)", CCITT Recommendation
              X.690, July 2002.

   [FIPS.186-4]
              National Institute of Standards and Technology, "Digital
              Signature Standard", FIPS PUB 186-4, 2013,
              <http://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.186-4.pdf>.

   [PKCS1]    RSA Laboratories, "RSA Encryption Standard, Version 1.5",
              PKCS 1, November 1993.

   [PKIX-EdDSA]
              Josefsson, S. and J. Schaad, "Algorithm Identifiers for
              Ed25519, Ed25519ph, Ed448, Ed448ph, X25519 and X448 for
              use in the Internet X.509 Public Key Infrastructure",
              August 2016, <https://tools.ietf.org/html/draft-ietf-
              curdle-pkix-01>.

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

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

   [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
              Identifiers for the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 3279, April 2002.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [RFC4366]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 4366, April 2006.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5289]  Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
              256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
              August 2008.




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   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
              for Security", RFC 7748, January 2016.

   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032, January 2017.

   [SECG-SEC2]
              CECG, "Recommended Elliptic Curve Domain Parameters",
              SEC 2, 2000.

12.2.  Informative References

   [FIPS.180-4]
              National Institute of Standards and Technology, "Secure
              Hash Standard (SHS)", FIPS PUB 180-4, August 2015,
              <http://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.180-4.pdf>.

   [I-D.ietf-tls-tls13]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-18 (work in progress),
              October 2016.

   [IEEE.P1363.1998]
              Institute of Electrical and Electronics Engineers,
              "Standard Specifications for Public Key Cryptography",
              IEEE Draft P1363, 1998.

   [Menezes]  Menezes, A. and B. Ustaoglu, "On Reusing Ephemeral Keys In
              Diffie-Hellman Key Agreement Protocols", IACR Menezes2008,
              December 2008.

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
              Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
              for Transport Layer Security (TLS)", RFC 4492, May 2006.

   [RFC7919]  Gillmor, D., "Negotiated Finite Field Diffie-Hellman
              Ephemeral Parameters for Transport Layer Security (TLS)",
              RFC 7919, DOI 10.17487/RFC7919, August 2016,
              <http://www.rfc-editor.org/info/rfc7919>.

Appendix A.  Equivalent Curves (Informative)

   All of the NIST curves [FIPS.186-4] and several of the ANSI curves
   [ANSI.X9-62.2005] are equivalent to curves listed in Section 5.1.1.
   In the following table, multiple names in one row represent aliases
   for the same curve.




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          Curve names chosen by different standards organizations

                  +-----------+------------+------------+
                  | SECG      | ANSI X9.62 | NIST       |
                  +-----------+------------+------------+
                  | sect163k1 |            | NIST K-163 |
                  | sect163r1 |            |            |
                  | sect163r2 |            | NIST B-163 |
                  | sect193r1 |            |            |
                  | sect193r2 |            |            |
                  | sect233k1 |            | NIST K-233 |
                  | sect233r1 |            | NIST B-233 |
                  | sect239k1 |            |            |
                  | sect283k1 |            | NIST K-283 |
                  | sect283r1 |            | NIST B-283 |
                  | sect409k1 |            | NIST K-409 |
                  | sect409r1 |            | NIST B-409 |
                  | sect571k1 |            | NIST K-571 |
                  | sect571r1 |            | NIST B-571 |
                  | secp160k1 |            |            |
                  | secp160r1 |            |            |
                  | secp160r2 |            |            |
                  | secp192k1 |            |            |
                  | secp192r1 | prime192v1 | NIST P-192 |
                  | secp224k1 |            |            |
                  | secp224r1 |            | NIST P-224 |
                  | secp256k1 |            |            |
                  | secp256r1 | prime256v1 | NIST P-256 |
                  | secp384r1 |            | NIST P-384 |
                  | secp521r1 |            | NIST P-521 |
                  +-----------+------------+------------+

        Table 4: Equivalent curves defined by SECG, ANSI, and NIST

Appendix B.  Differences from RFC 4492

   o  Added TLS 1.2
   o  Merged Errata
   o  Removed the ECDH key exchange algorithms: ECDH_RSA and ECDH_ECDSA
   o  Deprecated a bunch of ciphersuites:

         TLS_ECDH_ECDSA_WITH_NULL_SHA
         TLS_ECDH_ECDSA_WITH_RC4_128_SHA
         TLS_ECDH_ECDSA_WITH_3DES_EDE_CBC_SHA
         TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA
         TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA
         TLS_ECDH_RSA_WITH_NULL_SHA
         TLS_ECDH_RSA_WITH_RC4_128_SHA



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         TLS_ECDH_RSA_WITH_3DES_EDE_CBC_SHA
         TLS_ECDH_RSA_WITH_AES_128_CBC_SHA
         TLS_ECDH_RSA_WITH_AES_256_CBC_SHA
         All the other RC4 ciphersuites

   Removed unused curves and all but the uncompressed point format.

   Added X25519 and X448.

   Deprecated explicit curves.

   Removed restriction on signature algorithm in certificate.

Authors' Addresses

   Yoav Nir
   Check Point Software Technologies Ltd.
   5 Hasolelim st.
   Tel Aviv  6789735
   Israel

   Email: ynir.ietf@gmail.com


   Simon Josefsson
   SJD AB

   Email: simon@josefsson.org


   Manuel Pegourie-Gonnard
   Independent / PolarSSL

   Email: mpg@elzevir.fr

















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