| Network Working Group | J.M. Merkle |
| Internet-Draft | secunet Security Networks |
| Updates: 4492 (if approved) | M.L. Lochter |
| Intended status: Informational | Bundesamt fuer Sicherheit in der Informationstechnik (BSI) |
| Expires: January 09, 2014 | July 08, 2013 |
ECC Brainpool Curves for Transport Layer Security (TLS)
draft-merkle-tls-brainpool-04
This document specifies the use of several ECC Brainpool curves for authentication and key exchange in the Transport Layer Security (TLS) protocol.
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In [RFC5639], a new set of elliptic curve groups over finite prime fields for use in cryptographic applications was specified. These groups, denoted as ECC Brainpool curves, were generated in a verifiably pseudo-random way and comply with the security requirements of relevant standards from ISO [ISO1] [ISO2], ANSI [ANSI1], NIST [FIPS], and SecG [SEC2].
[RFC4492] defines the usage of elliptic curves for authentication and key agreement in TLS 1.0 and TLS 1.1, and these mechanisms are also applicable to TLS 1.2 [RFC5246]. While the ASN.1 object identifiers defined in [RFC5639] already allow usage of the ECC Brainpool curves for TLS (client or server) authentication through reference in X.509 certificates according to [RFC3279] and [RFC5480] , their negotiation for key exchange according to [RFC4492] requires the definition and assignment of additional NamedCurve IDs. This document specifies such values for three curves from [RFC5639].
According to [RFC4492], the name space NamedCurve is used for the negotiation of elliptic curve groups for key exchange during a handshake starting a new TLS session. This document adds new NamedCurve types to three elliptic curves defined in [RFC5639] as follows.
enum {
brainpoolP256r1(TBD1),
brainpoolP384r1(TBD2),
brainpoolP512r1(TBD3)
} NamedCurve;
These curves are suitable for use with DTLS [RFC6347].
Test vectors for a Diffie-Hellman key exchange using these elliptic curves are provided in Appendix A
IANA is requested to assign numbers for the ECC Brainpool curves listed in Section 2 to the Transport Layer Security (TLS) Parameters registry EC Named Curve [IANA-TLS] as follows.
| Value | Description | DTLS-OK | Reference |
|---|---|---|---|
| TBD1 | brainpoolP256r1 | Y | This doc |
| TBD2 | brainpoolP384r1 | Y | This doc |
| TBD3 | brainpoolP512r1 | Y | This doc |
The security considerations of [RFC5246] apply accordingly.
The confidentiality, authenticity and integrity of the TLS communication is limited by the weakest cryptographic primitive applied. In order to achieve a maximum security level when using one of the elliptic curves from Table 1 for authentication and / or key exchange in TLS, the key derivation function, the algorithms and key lengths of symmetric encryption and message authentication as well as the algorithm, bit length and hash function used for signature generation should be chosen according to the recommendations of [NIST800-57] and [RFC5639]. Furthermore, the private Diffie-Hellman keys should be selected with the same bit length as the order of the group generated by the base point G and with approximately maximum entropy.
Implementations of elliptic curve cryptography for TLS may be susceptible to side-channel attacks. Particular care should be taken for implementations that internally transform curve points to points on the corresponding "twisted curve", using the map (x',y') = (x*Z^2, y*Z^3) with the coefficient Z specified for that curve in [RFC5639], in order to take advantage of an an efficient arithmetic based on the twisted curve's special parameters (A = -3): although the twisted curve itself offers the same level of security as the corresponding random curve (through mathematical equivalence), an arithmetic based on small curve parameters may be harder to protect against side-channel attacks. General guidance on resistence of elliptic curve cryptography implementations against side-channel-attacks is given in [BSI1] and [HMV].
| [IANA-TLS] | Internet Assigned Numbers Authority, "Transport Layer Security (TLS) Parameters", . |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC4492] | Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C. and B. Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS)", RFC 4492, May 2006. |
| [RFC5246] | Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. |
| [RFC5639] | Lochter, M. and J. Merkle, "Elliptic Curve Cryptography (ECC) Brainpool Standard Curves and Curve Generation", RFC 5639, March 2010. |
| [RFC6347] | Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, January 2012. |
This section provides some test vectors for example Diffie-Hellman key exchanges using each of the curves defined in Table 1 . In all of the following sections the following notation is used: [SEC1].
The field elements x_qA, y_qA, x_qB, y_qB, x_Z, y_Z are represented as hexadecimal values using the FieldElement-to-OctetString conversion method specified in
Curve brainpoolP256r1
Curve brainpoolP384r1
Curve brainpoolP512r1