Network Working Group S. Josefsson Internet-Draft SJD AB Intended status: Standards Track June 16, 2015 Expires: December 18, 2015 EdDSA and Ed25519 for Transport Layer Security (TLS) draft-josefsson-tls-eddsa2-02 Abstract This document introduce the public-key signature algorithm EdDSA for use in Transport Layer Security (TLS). By defining new SignatureAlgorithm and NamedCurve enumeration values, we describe how EdDSA and Ed25519 is used for digital signatures in the existing ECDSA cipher suites. This is intended to work with any version of TLS and Datagram TLS. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Josefsson Expires December 18, 2015 [Page 1] Internet-Draft EdDSA and Ed25519 for TLS June 2015 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 1. Introduction TLS [RFC5246] and DTLS [RFC6347] support different key exchange algorithms and authentication mechanisms, and define the SignatureAlgorithm enumeration for different signature algorithms. In TLS-ECC [RFC4492], key exchange and authentication using ECC is specified, where the NamedCurve registry and associated TLS extensions are introduced. This document describes how to use EdDSA and Ed25519 [I-D.josefsson-eddsa-ed25519] as a new authentication mechanism in TLS. It define new SignatureAlgorithm and NamedCurve enumeration values and describe how these are used to negotiate EdDSA-based signatures. The goal is that all existing ECDSA cipher suites will, when the EdDSA SignatureAlgorithm is negotiated, use EdDSA instead of the traditional ECDSA signature algorithm. This document is a self-contained alternative to draft-josefsson-tls- eddsa. This document reuse the ECDSA cipher suites for EdDSA, whereas draft-josefsson-tls-eddsa specify new cipher suites for EdDSA. It is an open issue which approach is to be prefered. 1.1. Requirements Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. EdDSA SignatureAlgorithm Negotiation of the authentication mechanism is signalled by sending a SignatureAlgorithm value. Here we extend this enumeration for EdDSA. enum { eddsa(TBD1) } SignatureAlgorithm; EdDSA is suitable for use with TLS [RFC5246] and DTLS [RFC6347]. Note that EdDSA merely signals which signature algorithm to use, it does not imply any curve or hash parameter choice. Josefsson Expires December 18, 2015 [Page 2] Internet-Draft EdDSA and Ed25519 for TLS June 2015 For TLS 1.0 and 1.1 the DigitallySigned structure did not convey the signature algorithm to use, and hence implementations need to inspect the certificate to find out the signature algorithm to use. 3. Ed25519 NamedCurve Negotiation the elliptic curve is signalled with the Supported Elliptic Curves Extension extension. Here we extend the NamedCurve enumeration for EdDSA with the Ed25519 parameter choice. enum { ed25519(TBD3) } NamedCurve; 4. Using EdDSA in a handshake The following describe how EdDSA is used in a handshake. For ease of explanation, we assume a full handshake. [RFC4492] describes the semantics of ECC in TLS, including how resumed handshakes work, and this document refer to it for a complete discussion. A client that wish to negotiate use of EdDSA in a handshake MUST offer a ECDSA key exchange algorithm and send, in the same way as is done for other Signature Algorithms in ECDSA, a Signature Algorithm extension that include the "eddsa" SignatureAlgorithm value. The HashAlgorithm and NamedCurve types are also used, but depend on the actual EdDSA parameter choices. The HashAlgorithm value to specify for Ed25519 MUST be "sha512", to indicate use of Ed25519-SHA-512 as defined in [I-D.josefsson-eddsa-ed25519]. The meaning of using a "eddsa" SignatureAlgorithm with other HashAlgorithms is not defined here. The Supported Elliptic Curves Extension ("NamedCurve") must contain the relevant curve. Currently the only curve applicable to EdDSA is the "ed25519" NamedCurve value defined in this document. This is used to indicate request for Ed25519. Where applicable, the Supported Point Formats Extension ("ECPointFormat") value to use for EdDSA is "uncompressed". The format of EdDSA public-keys, e.g. Ed25519-SHA-512 public-keys, follows from the NamedCurve and HashAlgorithm value. 5. IANA Considerations IANA is requested to assign a number for EdDSA described in Section 2 to the Transport Layer Security (TLS) Parameters [IANA-TLS] registry under "SignatureAlgorithm" as follows. Josefsson Expires December 18, 2015 [Page 3] Internet-Draft EdDSA and Ed25519 for TLS June 2015 +-------+-------------+---------+-----------+ | Value | Description | DTLS-OK | Reference | +-------+-------------+---------+-----------+ | TBD1 | eddsa | Y | This doc | +-------+-------------+---------+-----------+ IANA is requested to assign a number for Ed25519 described in Section 3 to the Transport Layer Security (TLS) Parameters registry EC Named Curve [IANA-TLS] as follows. +-------+-------------+---------+-----------+ | Value | Description | DTLS-OK | Reference | +-------+-------------+---------+-----------+ | TBD2 | ed25519 | Y | This doc | +-------+-------------+---------+-----------+ 6. Security Considerations The security considerations of TLS [RFC5246], DTLS [RFC6347], TLS-ECC [RFC4492], and EdDSA and Ed25519 [I-D.josefsson-eddsa-ed25519] are inherited. As with all cryptographic algorithms and security protocols, the reader should stay informed about new research insights into the security of the algorithms and protocols involved. While discussed in the EdDSA/Ed25519 specification and papers, we would like to stress the significance of EdDSA/Ed25519 implementation security. In particular, implementations must avoid side-channel attacks by, for example, being constant-time. 7. Acknowledgements Thanks to Yoav Nir for suggesting re-use of ECDSA cipher suites with EdDSA, to reduce the cartesian product cipher suite explosion. Thanks to Klaus Hartke and Nicolas Williams for numerous fixes to the document. Other people who contributed include Ilari Liusvaara and Martin Thomson. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Josefsson Expires December 18, 2015 [Page 4] Internet-Draft EdDSA and Ed25519 for TLS June 2015 [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. [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, January 2012. [I-D.josefsson-eddsa-ed25519] Josefsson, S. and N. Moller, "EdDSA and Ed25519", draft- josefsson-eddsa-ed25519-02 (work in progress), February 2015. 8.2. Informative References [IANA-TLS] Internet Assigned Numbers Authority, "Transport Layer Security (TLS) Parameters", . Author's Address Simon Josefsson SJD AB Email: simon@josefsson.org Josefsson Expires December 18, 2015 [Page 5]