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rfc:rfc8422

Internet Engineering Task Force (IETF) Y. Nir Request for Comments: 8422 Check Point Obsoletes: 4492 S. Josefsson Category: Standards Track SJD AB ISSN: 2070-1721 M. Pegourie-Gonnard

                                                                   ARM
                                                           August 2018
          Elliptic Curve Cryptography (ECC) Cipher Suites
    for Transport Layer Security (TLS) Versions 1.2 and Earlier

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 the Elliptic Curve Digital Signature Algorithm (ECDSA) and
 Edwards-curve Digital Signature Algorithm (EdDSA) as authentication
 mechanisms.
 This document obsoletes RFC 4492.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8422.

Nir, et al. Standards Track [Page 1] RFC 8422 ECC Cipher Suites for TLS August 2018

Copyright Notice

 Copyright (c) 2018 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Nir, et al. Standards Track [Page 2] RFC 8422 ECC Cipher Suites for TLS August 2018

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   1.1.  Conventions Used in This Document . . . . . . . . . . . .   4
 2.  Key Exchange Algorithm  . . . . . . . . . . . . . . . . . . .   4
   2.1.  ECDHE_ECDSA . . . . . . . . . . . . . . . . . . . . . . .   6
   2.2.  ECDHE_RSA . . . . . . . . . . . . . . . . . . . . . . . .   7
   2.3.  ECDH_anon . . . . . . . . . . . . . . . . . . . . . . . .   7
   2.4.  Algorithms in Certificate Chains  . . . . . . . . . . . .   7
 3.  Client Authentication . . . . . . . . . . . . . . . . . . . .   8
   3.1.  ECDSA_sign  . . . . . . . . . . . . . . . . . . . . . . .   8
 4.  TLS Extensions for ECC  . . . . . . . . . . . . . . . . . . .   9
 5.  Data Structures and Computations  . . . . . . . . . . . . . .  10
   5.1.  Client Hello Extensions . . . . . . . . . . . . . . . . .  10
     5.1.1.  Supported Elliptic Curves Extension . . . . . . . . .  11
     5.1.2.  Supported Point Formats Extension . . . . . . . . . .  13
     5.1.3.  The signature_algorithms Extension and EdDSA  . . . .  13
   5.2.  Server Hello Extension  . . . . . . . . . . . . . . . . .  14
   5.3.  Server Certificate  . . . . . . . . . . . . . . . . . . .  15
   5.4.  Server Key Exchange . . . . . . . . . . . . . . . . . . .  16
     5.4.1.  Uncompressed Point Format for NIST Curves . . . . . .  19
   5.5.  Certificate Request . . . . . . . . . . . . . . . . . . .  20
   5.6.  Client Certificate  . . . . . . . . . . . . . . . . . . .  21
   5.7.  Client Key Exchange . . . . . . . . . . . . . . . . . . .  22
   5.8.  Certificate Verify  . . . . . . . . . . . . . . . . . . .  23
   5.9.  Elliptic Curve Certificates . . . . . . . . . . . . . . .  24
   5.10. ECDH, ECDSA, and RSA Computations . . . . . . . . . . . .  24
   5.11. Public Key Validation . . . . . . . . . . . . . . . . . .  26
 6.  Cipher Suites . . . . . . . . . . . . . . . . . . . . . . . .  26
 7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  27
 8.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
 9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
 10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
   10.1.  Normative References . . . . . . . . . . . . . . . . . .  29
   10.2.  Informative References . . . . . . . . . . . . . . . . .  31
 Appendix A.  Equivalent Curves (Informative)  . . . . . . . . . .  32
 Appendix B.  Differences from RFC 4492  . . . . . . . . . . . . .  33
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  34
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  34

Nir, et al. Standards Track [Page 3] RFC 8422 ECC Cipher Suites for TLS August 2018

1. Introduction

 This document describes additions to TLS to support ECC that are
 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 [TLS1.3] 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.  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", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

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.

Nir, et al. Standards Track [Page 4] RFC 8422 ECC Cipher Suites for TLS August 2018

 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.

Nir, et al. Standards Track [Page 5] RFC 8422 ECC Cipher Suites for TLS August 2018

        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.

Nir, et al. Standards Track [Page 6] RFC 8422 ECC Cipher Suites for TLS August 2018

 Both client and server perform an ECDH operation (see 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 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.

Nir, et al. Standards Track [Page 7] RFC 8422 ECC Cipher Suites for TLS August 2018

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.
 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 is 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.

Nir, et al. Standards Track [Page 8] RFC 8422 ECC Cipher Suites for TLS August 2018

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
 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.

Nir, et al. Standards Track [Page 9] RFC 8422 ECC Cipher Suites for TLS August 2018

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.
 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.

Nir, et al. Standards Track [Page 10] RFC 8422 ECC Cipher Suites for TLS August 2018

 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. Sections 5.3 and 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.
 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 "TLS 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

Nir, et al. Standards Track [Page 11] RFC 8422 ECC Cipher Suites for TLS August 2018

 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 (now titled "TLS Supported Groups") is
 maintained by IANA.  See Section 9 for information on how new value
 assignments are added.
         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

Nir, et al. Standards Track [Page 12] RFC 8422 ECC Cipher Suites for TLS August 2018

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 (now titled "TLS EC Point Formats") is
 maintained by IANA.  See Section 9 for information on how new value
 assignments are added.
 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-prehashed)
 forms of EdDSA do not hash the data before signing it.  For this
 reason, it does not make sense to combine them with a hash function
 in the extension.

Nir, et al. Standards Track [Page 13] RFC 8422 ECC Cipher Suites for TLS August 2018

 For bits-on-the-wire compatibility with TLS 1.3, we define a new
 dummy value in the "TLS HashAlgorithm" registry that we call
 "Intrinsic" (value 8), meaning that hashing is intrinsic to the
 signature algorithm.
 To represent ed25519 and ed448 in the signature_algorithms extension,
 the value shall be (8,7) and (8,8), 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
 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.

Nir, et al. Standards Track [Page 14] RFC 8422 ECC Cipher Suites for TLS August 2018

 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.  Sections 5.6 and 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 2 apply only to
 the server's certificate (first in the chain).
 +-------------+-----------------------------------------------------+
 | 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

Nir, et al. Standards Track [Page 15] RFC 8422 ECC Cipher Suites for TLS August 2018

 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 ECCurveType enum used to have values for explicit prime and for
 explicit char2 curves.  Those values are now deprecated, so only one
 value remains:
 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 (now titled "TLS EC Curve Types") is
 maintained by IANA.  See Section 9 for information on how new value
 assignments are added.

Nir, et al. Standards Track [Page 16] RFC 8422 ECC Cipher Suites for TLS August 2018

 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
 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.

Nir, et al. Standards Track [Page 17] RFC 8422 ECC Cipher Suites for TLS August 2018

 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.
      enum {
          ecdsa(3),
          ed25519(7)
          ed448(8)
      } 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.

Nir, et al. Standards Track [Page 18] RFC 8422 ECC Cipher Suites for TLS August 2018

 ECDSA signatures are generated and verified as described in
 Section 5.10.  SHA, in the above template for sha_hash, 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 [RFC8410] 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 include 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
 ECKAS-DH1 scheme from IEEE 1363 [IEEE.P1363].  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

Nir, et al. Standards Track [Page 19] RFC 8422 ECC Cipher Suites for TLS August 2018

 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:
 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.

Nir, et al. Standards Track [Page 20] RFC 8422 ECC Cipher Suites for TLS August 2018

 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:
 This message is used to authentically convey the client's static
 public key to the server.  ECC public keys must be encoded in
 certificates as described in Section 5.9.  The certificate MUST
 contain an ECDSA- or EdDSA-capable public key.
 NOTE: The client's Certificate message is capable of carrying a chain
 of certificates.  The restrictions mentioned above apply only to the
 client's certificate (first in the chain).
 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.

Nir, et al. Standards Track [Page 21] RFC 8422 ECC Cipher Suites for TLS August 2018

 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;
 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;

Nir, et al. Standards Track [Page 22] RFC 8422 ECC Cipher Suites for TLS August 2018

 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:
 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 [X.690] corresponding to the following
 ASN.1 notation [X.680].

Nir, et al. Standards Track [Page 23] RFC 8422 ECC Cipher Suites for TLS August 2018

         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 include 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.

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 [RFC8410].  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] using the ECKAS-DH1 scheme with
 the identity map as the 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 (Field

Nir, et al. Standards Track [Page 24] RFC 8422 ECC Cipher Suites for TLS August 2018

 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 Pseudorandom Function (PRF)
 serves as a KDF; in TLS 1.2, the KDF is determined by ciphersuite,
 and 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:
 (1) each party picks a secret key d uniformly at random and computes
 the corresponding public key x = X25519(d, G); (2) parties exchange
 their public keys and compute a shared secret as x_S = X25519(d,
 x_peer); and (3), 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 similarly, 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.
 All ECDSA computations MUST be performed according to ANSI X9.62 or
 its successors.  Data to be signed/verified is hashed, and the result
 runs 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 successors.  Data to be signed/verified is run through the EdDSA
 algorithm with no hashing (EdDSA will internally run the data through
 the "prehash" function PH).  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 8
 (Intrinsic).
 All RSA signatures must be generated and verified according to
 Section 7.2 of [RFC8017].

Nir, et al. Standards Track [Page 25] RFC 8422 ECC Cipher Suites for TLS August 2018

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.
     +-----------------------------------------+----------------+
     | 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

Nir, et al. Standards Track [Page 26] RFC 8422 ECC Cipher Suites for TLS August 2018

 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_SHA

7. Implementation Status

 Both ECDHE and ECDSA with the NIST curves are widely implemented and
 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 they are not yet as widely
 deployed.

8. Security Considerations

 Security issues are discussed throughout this memo.
 For TLS handshakes using ECC cipher suites, the security
 considerations in Appendix D of each of the three TLS base documents
 apply accordingly.
 Security discussions specific to ECC can be found in [IEEE.P1363] 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

Nir, et al. Standards Track [Page 27] RFC 8422 ECC Cipher Suites for TLS August 2018

 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], [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, defined the IANA
 registries for the following:
 o  Supported Groups (Section 5.1)
 o  EC Point Format (Section 5.1)
 o  EC Curve Type (Section 5.4)
 IANA has prepended "TLS" to the names of these 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".
 (RFC 4492 required IETF review.)
 All existing entries in the "ExtensionType Values", "TLS
 ClientCertificateType Identifiers", "TLS Cipher Suites", "TLS
 Supported Groups", "TLS EC Point Format", and "TLS EC Curve Type"
 registries that referred to RFC 4492 have been updated to refer to
 this document.
 IANA has assigned the value 29 to x25519 and the value 30 to x448 in
 the "TLS Supported Groups" registry.

Nir, et al. Standards Track [Page 28] RFC 8422 ECC Cipher Suites for TLS August 2018

 IANA has assigned two values in the "TLS SignatureAlgorithm" registry
 for ed25519 (7) and ed448 (8) with this document as reference.  This
 keeps compatibility with TLS 1.3.
 IANA has assigned one value from the "TLS HashAlgorithm" registry for
 Intrinsic (8) with DTLS-OK set to true (Y) and this document as
 reference.  This keeps compatibility with TLS 1.3.

10. References

10.1. 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, November 2005.
 [FIPS.186-4]
            National Institute of Standards and Technology, "Digital
            Signature Standard (DSS)", FIPS PUB 186-4,
            DOI 10.6028/NIST.FIPS.186-4, July 2013,
            <http://nvlpubs.nist.gov/nistpubs/FIPS/
            NIST.FIPS.186-4.pdf>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <https://www.rfc-editor.org/info/rfc2119>.
 [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
            RFC 2246, DOI 10.17487/RFC2246, January 1999,
            <https://www.rfc-editor.org/info/rfc2246>.
 [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, DOI 10.17487/RFC3279, April
            2002, <https://www.rfc-editor.org/info/rfc3279>.
 [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.1", RFC 4346,
            DOI 10.17487/RFC4346, April 2006,
            <https://www.rfc-editor.org/info/rfc4346>.

Nir, et al. Standards Track [Page 29] RFC 8422 ECC Cipher Suites for TLS August 2018

 [RFC4366]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
            and T. Wright, "Transport Layer Security (TLS)
            Extensions", RFC 4366, DOI 10.17487/RFC4366, April 2006,
            <https://www.rfc-editor.org/info/rfc4366>.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246,
            DOI 10.17487/RFC5246, August 2008,
            <https://www.rfc-editor.org/info/rfc5246>.
 [RFC5289]  Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
            256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
            DOI 10.17487/RFC5289, August 2008,
            <https://www.rfc-editor.org/info/rfc5289>.
 [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
            for Security", RFC 7748, DOI 10.17487/RFC7748, January
            2016, <https://www.rfc-editor.org/info/rfc7748>.
 [RFC8017]  Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
            "PKCS #1: RSA Cryptography Specifications Version 2.2",
            RFC 8017, DOI 10.17487/RFC8017, November 2016,
            <https://www.rfc-editor.org/info/rfc8017>.
 [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
            Signature Algorithm (EdDSA)", RFC 8032,
            DOI 10.17487/RFC8032, January 2017,
            <https://www.rfc-editor.org/info/rfc8032>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.
 [RFC8410]  Josefsson, S. and J. Schaad, "Algorithm Identifiers for
            Ed25519, Ed448, X25519 and X448 for Use in the Internet
            X.509 Public Key Infrastructure", RFC 8410,
            DOI 10.17487/RFC8410, August 2018,
            <https://www.rfc-editor.org/info/rfc8410>.
 [SECG-SEC2]
            Certicom Research, "SEC 2: Recommended Elliptic Curve
            Domain Parameters", Standards for Efficient Cryptography 2
            (SEC 2), Version 2.0, January 2010,
            <http://www.secg.org/sec2-v2.pdf>.
 [X.680]    ITU-T, "Abstract Syntax Notation One (ASN.1):
            Specification of basic notation", ITU-T Recommendation
            X.680, ISO/IEC 8824-1, August 2015.

Nir, et al. Standards Track [Page 30] RFC 8422 ECC Cipher Suites for TLS August 2018

 [X.690]    ITU-T, "Information technology-ASN.1 encoding rules:
            Specification of Basic Encoding Rules (BER), Canonical
            Encoding Rules (CER) and Distinguished Encoding Rules
            (DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1, August
            2015.

10.2. Informative References

 [FIPS.180-4]
            National Institute of Standards and Technology, "Secure
            Hash Standard (SHS)", FIPS PUB 180-4, DOI
            10.6028/NIST.FIPS.180-4, August 2015,
            <http://nvlpubs.nist.gov/nistpubs/FIPS/
            NIST.FIPS.180-4.pdf>.
 [IEEE.P1363]
            IEEE, "Standard Specifications for Public Key
            Cryptography", IEEE Std P1363,
            <http://ieeexplore.ieee.org/document/891000/>.
 [Menezes]  Menezes, A. and B. Ustaoglu, "On reusing ephemeral keys in
            Diffie-Hellman key agreement protocols", International
            Journal of Applied Cryptography, Vol. 2, Issue 2,
            DOI 10.1504/IJACT.2010.038308, January 2010.
 [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,
            DOI 10.17487/RFC4492, May 2006,
            <https://www.rfc-editor.org/info/rfc4492>.
 [RFC7919]  Gillmor, D., "Negotiated Finite Field Diffie-Hellman
            Ephemeral Parameters for Transport Layer Security (TLS)",
            RFC 7919, DOI 10.17487/RFC7919, August 2016,
            <https://www.rfc-editor.org/info/rfc7919>.
 [TLS1.3]   Rescorla, E., "The Transport Layer Security (TLS) Protocol
            Version 1.3", Work in Progress, draft-ietf-tls-tls13-28,
            March 2018.

Nir, et al. Standards Track [Page 31] RFC 8422 ECC Cipher Suites for TLS August 2018

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.
 The following table displays the curve names chosen by different
 standards organizations; multiple names in one row represent aliases
 for the same curve.
                +-----------+------------+------------+
                | 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

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Appendix B. Differences from RFC 4492

 o  Renamed EllipticCurveList to NamedCurveList.
 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
       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
 o  Removed unused curves and all but the uncompressed point format.
 o  Added X25519 and X448.
 o  Deprecated explicit curves.
 o  Removed restriction on signature algorithm in certificate.

Nir, et al. Standards Track [Page 33] RFC 8422 ECC Cipher Suites for TLS August 2018

Acknowledgements

 Most of the text in 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 authors would like to thank Nikos Mavrogiannopoulos, Martin
 Thomson, and Tanja Lange for contributions to this document.

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
 ARM
 Email: mpg@elzevir.fr

Nir, et al. Standards Track [Page 34]

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