< draft-ietf-tls-rfc4492bis-03.txt   draft-ietf-tls-rfc4492bis-04.txt >
TLS Working Group Y. Nir TLS Working Group Y. Nir
Internet-Draft Check Point Internet-Draft Check Point
Intended status: Standards Track July 6, 2015 Intended status: Standards Track S. Josefsson
Expires: January 7, 2016 Expires: April 21, 2016 SJD AB
M. Pegourie-Gonnard
Independent / PolarSSL
October 19, 2015
Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer
Security (TLS) Versions 1.2 and Earlier Security (TLS) Versions 1.2 and Earlier
draft-ietf-tls-rfc4492bis-03 draft-ietf-tls-rfc4492bis-04
Abstract Abstract
This document describes key exchange algorithms based on Elliptic This document describes key exchange algorithms based on Elliptic
Curve Cryptography (ECC) for the Transport Layer Security (TLS) Curve Cryptography (ECC) for the Transport Layer Security (TLS)
protocol. In particular, it specifies the use of Ephemeral Elliptic protocol. In particular, it specifies the use of Ephemeral Elliptic
Curve Diffie-Hellman (ECDHE) key agreement in a TLS handshake and the Curve Diffie-Hellman (ECDHE) key agreement in a TLS handshake and the
use of Elliptic Curve Digital Signature Algorithm (ECDSA) as a new use of Elliptic Curve Digital Signature Algorithm (ECDSA) as a new
authentication mechanism. authentication mechanism.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 7, 2016. This Internet-Draft will expire on April 21, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . 4 1.1. Conventions Used in This Document . . . . . . . . . . . . 4
2. Key Exchange Algorithm . . . . . . . . . . . . . . . . . . . 4 2. Key Exchange Algorithm . . . . . . . . . . . . . . . . . . . 4
2.1. ECDHE_ECDSA . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. ECDHE_ECDSA . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. ECDHE_RSA . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2. ECDHE_RSA . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. ECDH_anon . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3. ECDH_anon . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Client Authentication . . . . . . . . . . . . . . . . . . . . 6 3. Client Authentication . . . . . . . . . . . . . . . . . . . . 7
3.1. ECDSA_sign . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. ECDSA_sign . . . . . . . . . . . . . . . . . . . . . . . 7
4. TLS Extensions for ECC . . . . . . . . . . . . . . . . . . . 7 4. TLS Extensions for ECC . . . . . . . . . . . . . . . . . . . 8
5. Data Structures and Computations . . . . . . . . . . . . . . 8 5. Data Structures and Computations . . . . . . . . . . . . . . 8
5.1. Client Hello Extensions . . . . . . . . . . . . . . . . . 8 5.1. Client Hello Extensions . . . . . . . . . . . . . . . . . 9
5.1.1. Supported Elliptic Curves Extension . . . . . . . . . 10 5.1.1. Supported Elliptic Curves Extension . . . . . . . . . 10
5.1.2. Supported Point Formats Extension . . . . . . . . . . 11 5.1.2. Supported Point Formats Extension . . . . . . . . . . 11
5.2. Server Hello Extension . . . . . . . . . . . . . . . . . 11 5.2. Server Hello Extension . . . . . . . . . . . . . . . . . 12
5.3. Server Certificate . . . . . . . . . . . . . . . . . . . 12 5.3. Server Certificate . . . . . . . . . . . . . . . . . . . 13
5.4. Server Key Exchange . . . . . . . . . . . . . . . . . . . 13 5.4. Server Key Exchange . . . . . . . . . . . . . . . . . . . 14
5.5. Certificate Request . . . . . . . . . . . . . . . . . . . 17 5.5. Certificate Request . . . . . . . . . . . . . . . . . . . 17
5.6. Client Certificate . . . . . . . . . . . . . . . . . . . 18 5.6. Client Certificate . . . . . . . . . . . . . . . . . . . 18
5.7. Client Key Exchange . . . . . . . . . . . . . . . . . . . 19 5.7. Client Key Exchange . . . . . . . . . . . . . . . . . . . 19
5.8. Certificate Verify . . . . . . . . . . . . . . . . . . . 21 5.8. Certificate Verify . . . . . . . . . . . . . . . . . . . 20
5.9. Elliptic Curve Certificates . . . . . . . . . . . . . . . 22 5.9. Elliptic Curve Certificates . . . . . . . . . . . . . . . 21
5.10. ECDH, ECDSA, and RSA Computations . . . . . . . . . . . . 22 5.10. ECDH, ECDSA, and RSA Computations . . . . . . . . . . . . 21
5.11. Public Key Validation . . . . . . . . . . . . . . . . . . 22
6. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . . . 23 6. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 24 7. Security Considerations . . . . . . . . . . . . . . . . . . . 24
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
10. Version History for This Draft . . . . . . . . . . . . . . . 25 10. Version History for This Draft . . . . . . . . . . . . . . . 26
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
11.1. Normative References . . . . . . . . . . . . . . . . . . 26 11.1. Normative References . . . . . . . . . . . . . . . . . . 27
11.2. Informative References . . . . . . . . . . . . . . . . . 27 11.2. Informative References . . . . . . . . . . . . . . . . . 28
Appendix A. Equivalent Curves (Informative) . . . . . . . . . . 27 Appendix A. Equivalent Curves (Informative) . . . . . . . . . . 28
Appendix B. Differences from RFC 4492 . . . . . . . . . . . . . 28 Appendix B. Differences from RFC 4492 . . . . . . . . . . . . . 29
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 29 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction 1. Introduction
Elliptic Curve Cryptography (ECC) is emerging as an attractive Elliptic Curve Cryptography (ECC) has emerged as an attractive
public-key cryptosystem, in particular for mobile (i.e., wireless) public-key cryptosystem, in particular for mobile (i.e., wireless)
environments. Compared to currently prevalent cryptosystems such as environments. Compared to currently prevalent cryptosystems such as
RSA, ECC offers equivalent security with smaller key sizes. This is RSA, ECC offers equivalent security with smaller key sizes. This is
illustrated in the following table, based on [Lenstra_Verheul], which illustrated in the following table, based on [Lenstra_Verheul], which
gives approximate comparable key sizes for symmetric- and asymmetric- gives approximate comparable key sizes for symmetric- and asymmetric-
key cryptosystems based on the best-known algorithms for attacking key cryptosystems based on the best-known algorithms for attacking
them. them.
+-----------+-----+------------+ +-----------+-------+------------+
| Symmetric | ECC | DH/DSA/RSA | | Symmetric | ECC | DH/DSA/RSA |
+-----------+-----+------------+ +-----------+-------+------------+
| 80 | 163 | 1024 | | 80 | >=158 | 1024 |
| 112 | 233 | 2048 | | 112 | >=221 | 2048 |
| 128 | 283 | 3072 | | 128 | >=252 | 3072 |
| 192 | 409 | 7680 | | 192 | >=379 | 7680 |
| 256 | 571 | 15360 | | 256 | >=506 | 15360 |
+-----------+-----+------------+ +-----------+-------+------------+
Table 1: Comparable Key Sizes (in bits) Table 1: Comparable Key Sizes (in bits)
Smaller key sizes result in savings for power, memory, bandwidth, and Smaller key sizes result in savings for power, memory, bandwidth, and
computational cost that make ECC especially attractive for computational cost that make ECC especially attractive for
constrained environments. constrained environments.
This document describes additions to TLS to support ECC, applicable This document describes additions to TLS to support ECC, applicable
to TLS versions 1.0 [RFC2246], 1.1 [RFC4346], and 1.2 [RFC5246]. The 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 use of ECC in TLS 1.3 is defined in [I-D.ietf-tls-tls13], and is
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2. Key Exchange Algorithm 2. Key Exchange Algorithm
This document defines three new ECC-based key exchange algorithms for This document defines three new ECC-based key exchange algorithms for
TLS. All of them use Ephemeral ECDH (ECDHE) to compute the TLS TLS. All of them use Ephemeral ECDH (ECDHE) to compute the TLS
premaster secret, and they differ only in the mechanism (if any) used premaster secret, and they differ only in the mechanism (if any) used
to authenticate them. The derivation of the TLS master secret from to authenticate them. The derivation of the TLS master secret from
the premaster secret and the subsequent generation of bulk the premaster secret and the subsequent generation of bulk
encryption/MAC keys and initialization vectors is independent of the encryption/MAC keys and initialization vectors is independent of the
key exchange algorithm and not impacted by the introduction of ECC. key exchange algorithm and not impacted by the introduction of ECC.
The table below summarizes the new key exchange algorithms, which Table 2 summarizes the new key exchange algorithms. All of these key
mimic DHE_DSS, DHE_RSA, and DH_anon, respectively. exchange algorithms provide forward secrecy.
+-------------+---------------------------------------+ +-------------+------------------------------------------+
| Algorithm | Description | | Algorithm | Description |
+-------------+---------------------------------------+ +-------------+------------------------------------------+
| ECDHE_ECDSA | Ephemeral ECDH with ECDSA signatures. | | ECDHE_ECDSA | Ephemeral ECDH with ECDSA signatures. |
| ECDHE_RSA | Ephemeral ECDH with RSA signatures. | | ECDHE_RSA | Ephemeral ECDH with RSA signatures. |
| ECDH_anon | Anonymous ECDH, no signatures. | | ECDH_anon | Anonymous ephemeral ECDH, no signatures. |
+-------------+---------------------------------------+ +-------------+------------------------------------------+
Table 2: ECC Key Exchange Algorithms Table 2: ECC Key Exchange Algorithms
The ECDHE_ECDSA and ECDHE_RSA key exchange mechanisms provide forward These key exchanges are analogous to DHE_DSS, DHE_RSA, and DH_anon,
secrecy. With ECDHE_RSA, a server can reuse its existing RSA respectively.
certificate and easily comply with a constrained client's elliptic
curve p references (see Section 4). However, the computational cost With ECDHE_RSA, a server can reuse its existing RSA certificate and
incurred by a server is higher for ECDHE_RSA than for the traditional easily comply with a constrained client's elliptic curve preferences
RSA key exchange, which does not provide forward secrecy. (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 The anonymous key exchange algorithm does not provide authentication
of the server or the client. Like other anonymous TLS key exchanges, of the server or the client. Like other anonymous TLS key exchanges,
it is subject to man-in-the-middle attacks. Implementations of this it is subject to man-in-the-middle attacks. Implementations of this
algorithm SHOULD provide authentication by other means. algorithm SHOULD provide authentication by other means.
Note that there is no structural difference between ECDH and ECDSA Note that there is no structural difference between ECDH and ECDSA
keys. A certificate issuer may use X.509 v3 keyUsage and keys. A certificate issuer may use X.509 v3 keyUsage and
extendedKeyUsage extensions to restrict the use of an ECC public key extendedKeyUsage extensions to restrict the use of an ECC public key
to certain computations. This document refers to an ECC key as ECDH- to certain computations. This document refers to an ECC key as ECDH-
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2.2. ECDHE_RSA 2.2. ECDHE_RSA
This key exchange algorithm is the same as ECDHE_ECDSA except that This key exchange algorithm is the same as ECDHE_ECDSA except that
the server's certificate MUST contain an RSA public key authorized the server's certificate MUST contain an RSA public key authorized
for signing, and that the signature in the ServerKeyExchange message for signing, and that the signature in the ServerKeyExchange message
must be computed with the corresponding RSA private key. The server must be computed with the corresponding RSA private key. The server
certificate MUST be signed with RSA. certificate MUST be signed with RSA.
2.3. ECDH_anon 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. TBD: Do we
want to rename this so that it makes sense?
In ECDH_anon, the server's Certificate, the CertificateRequest, the In ECDH_anon, the server's Certificate, the CertificateRequest, the
client's Certificate, and the CertificateVerify messages MUST NOT be client's Certificate, and the CertificateVerify messages MUST NOT be
sent. sent.
The server MUST send an ephemeral ECDH public key and a specification The server MUST send an ephemeral ECDH public key and a specification
of the corresponding curve in the ServerKeyExchange message. These of the corresponding curve in the ServerKeyExchange message. These
parameters MUST NOT be signed. parameters MUST NOT be signed.
The client generates an ECDH key pair on the same curve as the 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 server's ephemeral ECDH key and sends its public key in the
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Actions of the receiver: Actions of the receiver:
A server that receives a ClientHello containing one or both of these A server that receives a ClientHello containing one or both of these
extensions MUST use the client's enumerated capabilities to guide its extensions MUST use the client's enumerated capabilities to guide its
selection of an appropriate cipher suite. One of the proposed ECC selection of an appropriate cipher suite. One of the proposed ECC
cipher suites must be negotiated only if the server can successfully cipher suites must be negotiated only if the server can successfully
complete the handshake while using the curves and point formats complete the handshake while using the curves and point formats
supported by the client (cf. Section 5.3 and Section 5.4). supported by the client (cf. Section 5.3 and Section 5.4).
NOTE: A server participating in an ECDHE-ECDSA key exchange may use NOTE: A server participating in an ECDHE-ECDSA key exchange may use
different curves for (i) the ECDSA key in its certificate, and (ii) different curves for the ECDSA key in its certificate, and for the
the ephemeral ECDH key in the ServerKeyExchange message. The server ephemeral ECDH key in the ServerKeyExchange message. The server MUST
must consider the extensions in both cases. consider the extensions in both cases.
If a server does not understand the Supported Elliptic Curves If a server does not understand the Supported Elliptic Curves
Extension, does not understand the Supported Point Formats Extension, Extension, does not understand the Supported Point Formats Extension,
or is unable to complete the ECC handshake while restricting itself or is unable to complete the ECC handshake while restricting itself
to the enumerated curves and point formats, it MUST NOT negotiate the to the enumerated curves and point formats, it MUST NOT negotiate the
use of an ECC cipher suite. Depending on what other cipher suites use of an ECC cipher suite. Depending on what other cipher suites
are proposed by the client and supported by the server, this may 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 result in a fatal handshake failure alert due to the lack of common
cipher suites. cipher suites.
5.1.1. Supported Elliptic Curves Extension 5.1.1. Supported Elliptic Curves Extension
RFC 4492 defined 25 different curves in the NamedCurve registry for RFC 4492 defined 25 different curves in the NamedCurve registry for
use in TLS. Only three have seen any use. This specification is use in TLS. Only three have seen any use. This specification is
deprecating the rest (with numbers 1-22). This specification also deprecating the rest (with numbers 1-22). This specification also
deprecates the explicit curves with identifiers 0xFF01 and 0xFF02. deprecates the explicit curves with identifiers 0xFF01 and 0xFF02.
This leaves only the following: It also adds the new curves defined in [CFRG-Curves]. The end result
is as follows:
enum { enum {
deprecated(1..22), deprecated(1..22),
secp256r1 (23), secp384r1 (24), secp521r1 (25), secp256r1 (23), secp384r1 (24), secp521r1 (25),
Curve25519(TBD1),
Curve448(TBD2),
reserved (0xFE00..0xFEFF), reserved (0xFE00..0xFEFF),
deprecated(0xFF01..0xFF02), deprecated(0xFF01..0xFF02),
(0xFFFF) (0xFFFF)
} NamedCurve; } NamedCurve;
Note that other specification have since added other values to this Note that other specification have since added other values to this
enumeration. enumeration.
secp256r1, etc: Indicates support of the corresponding named curve or secp256r1, etc: Indicates support of the corresponding named curve or
class of explicitly defined curves. The named curves defined here class of explicitly defined curves. The named curves secp256r1,
are those specified in SEC 2 [SECG-SEC2]. Note that many of these 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 curves are also recommended in ANSI X9.62 [ANSI.X9-62.2005] and FIPS
186-4 [FIPS.186-4]. Values 0xFE00 through 0xFEFF are reserved for 186-4 [FIPS.186-4]. Curve25519 and Curve448 are defined in
private use.
[CFRG-Curves]. Values 0xFE00 through 0xFEFF are reserved for private
use.
The NamedCurve name space is maintained by IANA. See Section 8 for The NamedCurve name space is maintained by IANA. See Section 8 for
information on how new value assignments are added. information on how new value assignments are added.
struct { struct {
NamedCurve elliptic_curve_list<1..2^16-1> NamedCurve elliptic_curve_list<1..2^16-1>
} EllipticCurveList; } EllipticCurveList;
Items in elliptic_curve_list are ordered according to the client's Items in elliptic_curve_list are ordered according to the client's
preferences (favorite choice first). preferences (favorite choice first).
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This message is sent when using the ECDHE_ECDSA, ECDHE_RSA, and This message is sent when using the ECDHE_ECDSA, ECDHE_RSA, and
ECDH_anon key exchange algorithms. ECDH_anon key exchange algorithms.
Meaning of this message: Meaning of this message:
This message is used to convey the server's ephemeral ECDH public key This message is used to convey the server's ephemeral ECDH public key
(and the corresponding elliptic curve domain parameters) to the (and the corresponding elliptic curve domain parameters) to the
client. 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:
Structure of this message: Structure of this message:
enum { explicit_prime (1), explicit_char2 (2), enum { deprecated (1..2), named_curve (3), reserved(248..255)
named_curve (3), reserved(248..255) } ECCurveType; } ECCurveType;
explicit_prime: Indicates the elliptic curve domain parameters are The value named_curve indicates that a named curve is used. This
conveyed verbosely, and the underlying finite field is a prime option SHOULD be used when applicable.
field.
explicit_char2: Indicates the elliptic curve domain parameters are
conveyed verbosely, and the underlying finite field is a
characteristic-2 field.
named_curve: Indicates that a named curve is used. This option
SHOULD be used when applicable.
Values 248 through 255 are reserved for private use. Values 248 through 255 are reserved for private use.
The ECCurveType name space is maintained by IANA. See Section 8 for The ECCurveType name space is maintained by IANA. See Section 8 for
information on how new value assignments are added. information on how new value assignments are added.
struct { RFC 4492 had a specification for an ECCurve structure and an
opaque a <1..2^8-1>; ECBasisType structure. Both of these are omitted now because they
opaque b <1..2^8-1>; were only used with the now deprecated explicit curves.
} ECCurve;
a, b: These parameters specify the coefficients of the elliptic
curve. Each value contains the byte string representation of a
field element following the conversion routine in Section 4.3.3 of
[ANSI.X9-62.2005].
struct { struct {
opaque point <1..2^8-1>; opaque point <1..2^8-1>;
} ECPoint; } 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 or compressed format; it MUST conform
to what the client has requested through a Supported Point Formats
Extension if this extension was used.
enum { This is the byte string representation of an elliptic curve point
ec_basis_trinomial(1), ec_basis_pentanomial(2), following the conversion routine in Section 4.3.6 of
(255) [ANSI.X9-62.2005]. This byte string may represent an elliptic curve
} ECBasisType; point in uncompressed or compressed format; it MUST conform to what
ec_basis_trinomial: Indicates representation of a characteristic-2 the client has requested through a Supported Point Formats Extension
field using a trinomial basis. if this extension was used. For the Curve25519 and Curve448 curves,
ec_basis_pentanomial: Indicates representation of a characteristic-2 the only valid representation is the one specified in [CFRG-Curves] -
field using a pentanomial basis. a 32- or 56-octet representation of the u value of the point.
struct { struct {
ECCurveType curve_type; ECCurveType curve_type;
select (curve_type) { select (curve_type) {
case explicit_prime:
opaque prime_p <1..2^8-1>;
ECCurve curve;
ECPoint base;
opaque order <1..2^8-1>;
opaque cofactor <1..2^8-1>;
case explicit_char2:
uint16 m;
ECBasisType basis;
select (basis) {
case ec_basis_trinomial:
opaque k <1..2^8-1>;
case ec_basis_pentanomial:
opaque k1 <1..2^8-1>;
opaque k2 <1..2^8-1>;
opaque k3 <1..2^8-1>;
};
ECCurve curve;
ECPoint base;
opaque order <1..2^8-1>;
opaque cofactor <1..2^8-1>;
case named_curve: case named_curve:
NamedCurve namedcurve; NamedCurve namedcurve;
}; };
} ECParameters; } ECParameters;
curve_type: This identifies the type of the elliptic curve domain
parameters.
prime_p: This is the odd prime defining the field Fp.
curve: Specifies the coefficients a and b of the elliptic curve E.
base: Specifies the base point G on the elliptic curve.
order: Specifies the order n of the base point.
cofactor: Specifies the cofactor h = #E(Fq)/n, where #E(Fq)
represents the number of points on the elliptic curve E defined
over the field Fq (either Fp or F2^m).
m: This is the degree of the characteristic-2 field F2^m.
k: The exponent k for the trinomial basis representation x^m + x^k+1.
k1, k2, k3: The exponents for the pentanomial representation x^m + This identifies the type of the elliptic curve domain parameters.
x^k3 + x^k2 + x^k1 + 1 (such that k3 > k2 > k1).
namedcurve: Specifies a recommended set of elliptic curve domain Specifies a recommended set of elliptic curve domain parameters. All
parameters. All those values of NamedCurve are allowed that refer those values of NamedCurve are allowed that refer to a specific
to a specific curve. Values of NamedCurve that indicate support curve. Values of NamedCurve that indicate support for a class of
for a class of explicitly defined curves are not allowed here explicitly defined curves are not allowed here (they are only
(they are only permissible in the ClientHello extension); this permissible in the ClientHello extension); this applies to
applies to arbitrary_explicit_prime_curves(0xFF01) and arbitrary_explicit_prime_curves(0xFF01) and
arbitrary_explicit_char2_curves(0xFF02). arbitrary_explicit_char2_curves(0xFF02).
struct { struct {
ECParameters curve_params; ECParameters curve_params;
ECPoint public; ECPoint public;
} ServerECDHParams; } ServerECDHParams;
curve_params: Specifies the elliptic curve domain parameters
associated with the ECDH public key. Specifies the elliptic curve domain parameters associated with the
public: The ephemeral ECDH public key. ECDH public key.
The ephemeral ECDH public key.
The ServerKeyExchange message is extended as follows. The ServerKeyExchange message is extended as follows.
enum { ec_diffie_hellman } KeyExchangeAlgorithm; enum { ec_diffie_hellman } KeyExchangeAlgorithm;
ec_diffie_hellman: Indicates the ServerKeyExchange message contains ec_diffie_hellman: Indicates the ServerKeyExchange message contains
an ECDH public key. an ECDH public key.
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case ec_diffie_hellman: case ec_diffie_hellman:
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5.9. Elliptic Curve Certificates 5.9. Elliptic Curve Certificates
X.509 certificates containing ECC public keys or signed using ECDSA X.509 certificates containing ECC public keys or signed using ECDSA
MUST comply with [RFC3279] or another RFC that replaces or extends MUST comply with [RFC3279] or another RFC that replaces or extends
it. Clients SHOULD use the elliptic curve domain parameters it. Clients SHOULD use the elliptic curve domain parameters
recommended in ANSI X9.62, FIPS 186-4, and SEC 2 [SECG-SEC2]. recommended in ANSI X9.62, FIPS 186-4, and SEC 2 [SECG-SEC2].
5.10. ECDH, ECDSA, and RSA Computations 5.10. ECDH, ECDSA, and RSA Computations
All ECDH calculations (including parameter and key generation as well All ECDH calculations for the NIST curves (including parameter and
as the shared secret calculation) are performed according to key generation as well as the shared secret calculation) are
[IEEE.P1363.1998] using the ECKAS-DH1 scheme with the identity map as performed according to [IEEE.P1363.1998] using the ECKAS-DH1 scheme
key derivation function (KDF), so that the premaster secret is the with the identity map as key derivation function (KDF), so that the
x-coordinate of the ECDH shared secret elliptic curve point premaster secret is the x-coordinate of the ECDH shared secret
represented as an octet string. Note that this octet string (Z in elliptic curve point represented as an octet string. Note that this
IEEE 1363 terminology) as output by FE2OSP, the Field Element to octet string (Z in IEEE 1363 terminology) as output by FE2OSP, the
Octet String Conversion Primitive, has constant length for any given Field Element to Octet String Conversion Primitive, has constant
field; leading zeros found in this octet string MUST NOT be length for any given field; leading zeros found in this octet string
truncated. MUST NOT be truncated.
(Note that this use of the identity KDF is a technicality. The (Note that this use of the identity KDF is a technicality. The
complete picture is that ECDH is employed with a non-trivial KDF complete picture is that ECDH is employed with a non-trivial KDF
because TLS does not directly use the premaster secret for anything 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 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 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 1.2 the KDF is determined by ciphersuite; it is conceivable that
future TLS versions or new TLS extensions introduced in the future future TLS versions or new TLS extensions introduced in the future
may vary this computation.) may vary this computation.)
An ECDHE key exchange using Curve25519 goes as follows. Each party
picks a secret key d uniformly at random and computes the
corresponding public key x = Curve25519(d, G). Parties exchange
their public keys and compute a shared secret as x_S = Curve25519(d,
x_peer). ECDHE for Curve448 works similarily, replacing Curve25519
with Curve448. The derived shared secret is used directly as the
premaster secret, which is always exactly 32 bytes when ECDHE with
Curve25519 is used and 56 bytes when ECDHE with Curve448 is used.
All ECDSA computations MUST be performed according to ANSI X9.62 or All ECDSA computations MUST be performed according to ANSI X9.62 or
its successors. Data to be signed/verified is hashed, and the result its successors. Data to be signed/verified is hashed, and the result
run directly through the ECDSA algorithm with no additional hashing. run directly through the ECDSA algorithm with no additional hashing.
The default hash function is SHA-1 [FIPS.180-2], and sha_size (see The default hash function is SHA-1 [FIPS.180-2], and sha_size (see
Section 5.4 and Section 5.8) is 20. However, an alternative hash Section 5.4 and Section 5.8) is 20. However, an alternative hash
function, such as one of the new SHA hash functions specified in FIPS function, such as one of the new SHA hash functions specified in FIPS
180-2 [FIPS.180-2], may be used instead. 180-2 [FIPS.180-2], may be used instead.
RFC 4492 anticipated the standardization of a mechanism for RFC 4492 anticipated the standardization of a mechanism for
specifying the required hash function in the certificate, perhaps in specifying the required hash function in the certificate, perhaps in
the parameters field of the subjectPublicKeyInfo. Such the parameters field of the subjectPublicKeyInfo. Such
standardization never took place, and as a result, SHA-1 is used in standardization never took place, and as a result, SHA-1 is used in
TLS 1.1 and earlier. TLS 1.2 added a SignatureAndHashAlgorithm TLS 1.1 and earlier. TLS 1.2 added a SignatureAndHashAlgorithm
parameter to the DigitallySigned struct, thus allowing agility in parameter to the DigitallySigned struct, thus allowing agility in
choosing the signature hash. choosing the signature hash.
All RSA signatures must be generated and verified according to All RSA signatures must be generated and verified according to
[PKCS1] block type 1. [PKCS1] block type 1.
5.11. Public Key Validation
With the NIST curves, each party must validate the public key sent by
its peer before performing cryptographic computations with it.
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.
Curve25519 was designed in a way that the result of Curve25519(x, d)
will never reveal information about d, provided it was chosen as
prescribed, for any value of x.
Let's define legitimate values of x as the values that can be
obtained as x = Curve25519(G, d') for some d, and call the other
values illegitimate. The definition of the Curve25519 function shows
that legitimate values all share the following property: the high-
order bit of the last byte is not set.
Since there are some implementation of the Curve25519 function that
impose this restriction on their input and others that don't,
implementations of Curve25519 in TLS SHOULD reject public keys when
the high-order bit of the last byte is set (in other words, when the
value of the leftmost byte is greater than 0x7F) in order to prevent
implementation fingerprinting.
Other than this recommended check, implementations do not need to
ensure that the public keys they receive are legitimate: this is not
necessary for security with Curve25519.
6. Cipher Suites 6. Cipher Suites
The table below defines new ECC cipher suites that use the key The table below defines new ECC cipher suites that use the key
exchange algorithms specified in Section 2. exchange algorithms specified in Section 2.
+---------------------------------------+----------------+ +---------------------------------------+----------------+
| CipherSuite | Identifier | | CipherSuite | Identifier |
+---------------------------------------+----------------+ +---------------------------------------+----------------+
| TLS_ECDHE_ECDSA_WITH_NULL_SHA | { 0xC0, 0x06 } | | TLS_ECDHE_ECDSA_WITH_NULL_SHA | { 0xC0, 0x06 } |
| TLS_ECDHE_ECDSA_WITH_RC4_128_SHA | { 0xC0, 0x07 } | | TLS_ECDHE_ECDSA_WITH_RC4_128_SHA | { 0xC0, 0x07 } |
skipping to change at page 25, line 10 skipping to change at page 25, line 48
[RFC4492], the predecessor of this document has already defined the [RFC4492], the predecessor of this document has already defined the
IANA registries for the following: IANA registries for the following:
o NamedCurve Section 5.1 o NamedCurve Section 5.1
o ECPointFormat Section 5.1 o ECPointFormat Section 5.1
o ECCurveType Section 5.4 o ECCurveType Section 5.4
For each name space, this document defines the initial value For each name space, this document defines the initial value
assignments and defines a range of 256 values (NamedCurve) or eight assignments and defines a range of 256 values (NamedCurve) or eight
values (ECPointFormat and ECCurveType) reserved for Private Use. Any values (ECPointFormat and ECCurveType) reserved for Private Use. Any
additional assignments require IETF Consensus action. additional assignments require IETF Review.
NOTE: IANA, please update the registries to reflect the new policy
name.
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 assign two values from the NamedCurve registry
with names Curve25519(TBD1) and Curve448(TBD2) with this document as
reference.
9. Acknowledgements 9. Acknowledgements
Most of the text is this document is taken from [RFC4492], the Most of the text is this document is taken from [RFC4492], the
predecessor of this document. The authors of that document were: predecessor of this document. The authors of that document were:
o Simon Blake-Wilson o Simon Blake-Wilson
o Nelson Bolyard o Nelson Bolyard
o Vipul Gupta o Vipul Gupta
o Chris Hawk o Chris Hawk
skipping to change at page 26, line 28 skipping to change at page 27, line 28
Specification of basic notation", CCITT Recommendation Specification of basic notation", CCITT Recommendation
X.680, July 2002. X.680, July 2002.
[CCITT.X690] [CCITT.X690]
International Telephone and Telegraph Consultative International Telephone and Telegraph Consultative
Committee, "ASN.1 encoding rules: Specification of basic Committee, "ASN.1 encoding rules: Specification of basic
encoding Rules (BER), Canonical encoding rules (CER) and encoding Rules (BER), Canonical encoding rules (CER) and
Distinguished encoding rules (DER)", CCITT Recommendation Distinguished encoding rules (DER)", CCITT Recommendation
X.690, July 2002. X.690, July 2002.
[CFRG-Curves]
Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", draft-irtf-cfrg-curves-11 (work in
progress), October 2015.
[FIPS.186-4] [FIPS.186-4]
National Institute of Standards and Technology, "Digital National Institute of Standards and Technology, "Digital
Signature Standard", FIPS PUB 186-4, 2013, Signature Standard", FIPS PUB 186-4, 2013,
<http://nvlpubs.nist.gov/nistpubs/FIPS/ <http://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.186-4.pdf>. NIST.FIPS.186-4.pdf>.
[PKCS1] RSA Laboratories, "RSA Encryption Standard, Version 1.5", [PKCS1] RSA Laboratories, "RSA Encryption Standard, Version 1.5",
PKCS 1, November 1993. PKCS 1, November 1993.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
skipping to change at page 29, line 10 skipping to change at page 30, line 10
TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA
TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA
TLS_ECDH_RSA_WITH_NULL_SHA TLS_ECDH_RSA_WITH_NULL_SHA
TLS_ECDH_RSA_WITH_RC4_128_SHA TLS_ECDH_RSA_WITH_RC4_128_SHA
TLS_ECDH_RSA_WITH_3DES_EDE_CBC_SHA TLS_ECDH_RSA_WITH_3DES_EDE_CBC_SHA
TLS_ECDH_RSA_WITH_AES_128_CBC_SHA TLS_ECDH_RSA_WITH_AES_128_CBC_SHA
TLS_ECDH_RSA_WITH_AES_256_CBC_SHA TLS_ECDH_RSA_WITH_AES_256_CBC_SHA
Removed unused curves and all but the uncompressed point format. Removed unused curves and all but the uncompressed point format.
Author's Address Added Curve25519 and Curve448.
Deprecated explicit curves.
Authors' Addresses
Yoav Nir Yoav Nir
Check Point Software Technologies Ltd. Check Point Software Technologies Ltd.
5 Hasolelim st. 5 Hasolelim st.
Tel Aviv 6789735 Tel Aviv 6789735
Israel Israel
Email: ynir.ietf@gmail.com 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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