--- 1/draft-ietf-ipsecme-safecurves-04.txt 2016-10-11 13:15:59.386269175 -0700 +++ 2/draft-ietf-ipsecme-safecurves-05.txt 2016-10-11 13:15:59.406269684 -0700 @@ -1,19 +1,19 @@ Network Working Group Y. Nir Internet-Draft Check Point Intended status: Standards Track S. Josefsson -Expires: March 3, 2017 SJD - August 30, 2016 +Expires: April 14, 2017 SJD + October 11, 2016 Curve25519 and Curve448 for IKEv2 Key Agreement - draft-ietf-ipsecme-safecurves-04 + draft-ietf-ipsecme-safecurves-05 Abstract This document describes the use of Curve25519 and Curve448 for ephemeral key exchange in the Internet Key Exchange (IKEv2) protocol. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. @@ -21,21 +21,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on March 3, 2017. + This Internet-Draft will expire on April 14, 2017. Copyright Notice Copyright (c) 2016 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -59,51 +59,53 @@ 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . 5 Appendix A. Numerical Example for Curve25519 . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction The "Elliptic Curves for Security" document [RFC7748] describes two elliptic curves: Curve25519 and Curve448, as well as the X25519 and - X448 functions for performing key agreement (Diffie-Hellman) + X448 functions for performing key agreement using Diffie-Hellman operations with these curves. The curves and functions are designed for both performance and security. Elliptic curve Diffie-Hellman [RFC5903] has been specified for the - Internet Key Exchange (IKEv2 - [RFC7296]) for almost ten years. That - document specified the so-called NIST curves. The state of the art - has advanced since then. More modern curves allow faster - implementations while making it much easier to write constant-time - implementations free from time-based side-channel attacks. This - document defines two such curves for use in IKE. See [Curve25519] - for details about the speed and security of the Curve25519 function. + Internet Key Exchange (IKEv2 - [RFC7296]) for almost ten years. RFC + 5903 and its predecessor specified the so-called NIST curves. The + state of the art has advanced since then. More modern curves allow + faster implementations while making it much easier to write constant- + time implementations resilient to time-based side-channel attacks. + This document defines two such curves for use in IKE. See + [Curve25519] for details about the speed and security of the + Curve25519 function. 1.1. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Curve25519 & Curve448 - All cryptographic computations are done using the X25519 and X448 - functions defined in [RFC7748]. All related parameters (for example, - the base point) and the encoding (in particular, pruning the least/ - most significant bits and use of little-endian encoding) are - inherited from [RFC7748]. + Implementations of Curve25519 and Curve448 in IKEv2 SHALL follow the + steps described in this section. All cryptographic computations are + done using the X25519 and X448 functions defined in [RFC7748]. All + related parameters (for example, the base point) and the encoding (in + particular, pruning the least/most significant bits and use of + little-endian encoding) are compliant with [RFC7748]. An ephemeral Diffie-Hellman key exchange using Curve25519 or Curve448 - goes as follows: Each party picks a secret key d uniformly at random - and computes the corresponding public key. "X" is used below to - denote either X25519 or X448, and "G" is used to denote the + is performed as follows: Each party picks a secret key d uniformly at + random and computes the corresponding public key. "X" is used below + to denote either X25519 or X448, and "G" is used to denote the corresponding base point: pub_mine = X(d, G) Parties exchange their public keys (see Section 3.1) and compute a shared secret: SHARED_SECRET = X(d, pub_peer). This shared secret is used directly as the value denoted g^ir in @@ -131,84 +133,86 @@ | Diffie-Hellman Group Num | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Key Exchange Data ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o Payload Length - For Curve25519 the public key is 32 octets, so the Payload Length field will be 40, and for Curve448 the public key is 56 octets, so the Payload Length field will be 64. + o The Diffie-Hellman Group Num is TBA1 for Curve25519, or TBA2 for Curve448. - o The Key Exchange Data is the 32 or 56 octets as described in section 6 of [RFC7748] 3.2. Recipient Tests - This document matches the discussion in [RFC7748] related to - receiving and accepting incompatible point formats. In particular, + Receiving and handling of incompatible point formats MUST follow the + considerations described in section 5 of [RFC7748]. In particular, receiving entities MUST mask the most-significant bit in the final byte for X25519 (but not X448), and implementations MUST accept non- - canonical values. See section 5 of [RFC7748] for further discussion. + canonical values. 4. Security Considerations Curve25519 and Curve448 are designed to facilitate the production of high-performance constant-time implementations. Implementors are encouraged to use a constant-time implementation of the functions. - This point is of crucial importance if the implementation chooses to - reuse its supposedly ephemeral key pair for many key exchanges, which - some implementations do in order to improve performance. + This point is of crucial importance especially if the implementation + chooses to reuse its ephemeral key pair in many key exchanges for + performance reasons. Curve25519 is intended for the ~128-bit security level, comparable to the 256-bit random ECP group (group 19) defined in RFC 5903, also known as NIST P-256 or secp256r1. Curve448 is intended for the ~224-bit security level. While the NIST curves are advertised as being chosen verifiably at random, there is no explanation for the seeds used to generate them. - In contrast, the process used to pick these curves is fully - documented and rigid enough so that independent verification has been - done. This is widely seen as a security advantage, since it prevents - the generating party from maliciously manipulating the parameters. + In contrast, the process used to pick Curve25519 and Curve448 is + fully documented and rigid enough so that independent verification + can and has been done. This is widely seen as a security advantage, + since it prevents the generating party from maliciously manipulating + the parameters. - Another family of curves available in IKE, generated in a fully - verifiable way, is the Brainpool curves [RFC6954]. For example, - brainpoolP256 (group 28) is expected to provide a level of security - comparable to Curve25519 and NIST P-256. However, due to the use of - pseudo-random prime, it is significantly slower than NIST P-256, - which is itself slower than Curve25519. + Another family of curves available in IKE that were generated in a + fully verifiable way, is the Brainpool curves [RFC6954]. For + example, brainpoolP256 (group 28) is expected to provide a level of + security comparable to Curve25519 and NIST P-256. However, due to + the use of pseudo-random prime, it is significantly slower than NIST + P-256, which is itself slower than Curve25519. 5. IANA Considerations IANA is requested to assign two values from the IKEv2 "Transform Type 4 - Diffie-Hellman Group Transform IDs" registry, with names "Curve25519" and "Curve448" and this document as reference. The Recipient Tests field should also point to this document: +--------+------------+---------------------+-----------+ | Number | Name | Recipient Tests | Reference | +--------+------------+---------------------+-----------+ | TBA1 | Curve25519 | RFCxxxx Section 3.2 | RFCxxxx | | TBA2 | Curve448 | RFCxxxx Section 3.2 | RFCxxxx | +--------+------------+---------------------+-----------+ Table 1: New Transform Type 4 Values 6. Acknowledgements Curve25519 was designed by D. J. Bernstein and the parameters for - Curve448 ("Goldilocks") is by Mike Hamburg. The specification of - algorithms, wire format and other considerations are in RFC 7748 by - Adam Langley, Mike Hamburg, and Sean Turner. + Curve448 ("Goldilocks") were defined by Mike Hamburg. The + specification of algorithms, wire format and other considerations are + documented in RFC 7748 by Adam Langley, Mike Hamburg, and Sean + Turner. The example in Appendix A was calculated using the master version of OpenSSL, retrieved on August 4th, 2016. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.