draft-ietf-ipsecme-safecurves-03.txt   draft-ietf-ipsecme-safecurves-04.txt 
Network Working Group Y. Nir Network Working Group Y. Nir
Internet-Draft Check Point Internet-Draft Check Point
Intended status: Standards Track S. Josefsson Intended status: Standards Track S. Josefsson
Expires: February 10, 2017 SJD Expires: March 3, 2017 SJD
August 9, 2016 August 30, 2016
Curve25519 and Curve448 for IKEv2 Key Agreement Curve25519 and Curve448 for IKEv2 Key Agreement
draft-ietf-ipsecme-safecurves-03 draft-ietf-ipsecme-safecurves-04
Abstract Abstract
This document describes the use of Curve25519 and Curve448 for This document describes the use of Curve25519 and Curve448 for
ephemeral key exchange in the Internet Key Exchange (IKEv2) protocol. ephemeral key exchange in the Internet Key Exchange (IKEv2) protocol.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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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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This Internet-Draft will expire on February 10, 2017. This Internet-Draft will expire on March 3, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 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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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction 1. Introduction
The "Elliptic Curves for Security" document [RFC7748] describes two The "Elliptic Curves for Security" document [RFC7748] describes two
elliptic curves: Curve25519 and Curve448, as well as the X25519 and 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 (Diffie-Hellman)
operations with these curves. The curves and functions are designed operations with these curves. The curves and functions are designed
for both performance and security. for both performance and security.
Almost ten years ago the "ECP Groups for IKE and IKEv2" document Elliptic curve Diffie-Hellman [RFC5903] has been specified for the
[RFC4753] specified the first elliptic curve Diffie-Hellman groups Internet Key Exchange (IKEv2 - [RFC7296]) for almost ten years. That
for the Internet Key Exchange protocol (IKEv2 - [RFC7296]). These document specified the so-called NIST curves. The state of the art
were the so-called NIST curves. The state of the art has advanced has advanced since then. More modern curves allow faster
since then. More modern curves allow faster implementations while implementations while making it much easier to write constant-time
making it much easier to write constant-time implementations free implementations free from time-based side-channel attacks. This
from time-based side-channel attacks. This document defines two such document defines two such curves for use in IKE. See [Curve25519]
curves for use in IKE. See [Curve25519] for details about the speed for details about the speed and security of the Curve25519 function.
and security of the Curve25519 function.
1.1. Conventions Used in This Document 1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Curve25519 & Curve448 2. Curve25519 & Curve448
All cryptographic computations are done using the X25519 and X448 All cryptographic computations are done using the X25519 and X448
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4. Security Considerations 4. Security Considerations
Curve25519 and Curve448 are designed to facilitate the production of Curve25519 and Curve448 are designed to facilitate the production of
high-performance constant-time implementations. Implementors are high-performance constant-time implementations. Implementors are
encouraged to use a constant-time implementation of the functions. encouraged to use a constant-time implementation of the functions.
This point is of crucial importance if the implementation chooses to This point is of crucial importance if the implementation chooses to
reuse its supposedly ephemeral key pair for many key exchanges, which reuse its supposedly ephemeral key pair for many key exchanges, which
some implementations do in order to improve performance. some implementations do in order to improve performance.
Curve25519 is intended for the ~128-bit security level, comparable to Curve25519 is intended for the ~128-bit security level, comparable to
the 256-bit random ECP group (group 19) defined in RFC 4753, also 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 known as NIST P-256 or secp256r1. Curve448 is intended for the
~224-bit security level. ~224-bit security level.
While the NIST curves are advertised as being chosen verifiably at While the NIST curves are advertised as being chosen verifiably at
random, there is no explanation for the seeds used to generate them. random, there is no explanation for the seeds used to generate them.
In contrast, the process used to pick these curves is fully In contrast, the process used to pick these curves is fully
documented and rigid enough so that independent verification has been documented and rigid enough so that independent verification has been
done. This is widely seen as a security advantage, since it prevents done. This is widely seen as a security advantage, since it prevents
the generating party from maliciously manipulating the parameters. the generating party from maliciously manipulating the parameters.
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[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, January 2016. for Security", RFC 7748, January 2016.
7.2. Informative References 7.2. Informative References
[Curve25519] [Curve25519]
Bernstein, J., "Curve25519: New Diffie-Hellman Speed Bernstein, J., "Curve25519: New Diffie-Hellman Speed
Records", LNCS 3958, February 2006, Records", LNCS 3958, February 2006,
<http://dx.doi.org/10.1007/11745853_14>. <http://dx.doi.org/10.1007/11745853_14>.
[RFC4753] Fu, D. and J. Solinas, "ECP Groups For IKE and IKEv2", [RFC5903] Fu, D. and J. Solinas, "Elliptic Curve Groups modulo a
RFC 4753, January 2007. Prime (ECP Groups) for IKE and IKEv2", RFC 5903, June
2010.
[RFC6954] Merkle, J. and M. Lochter, "Using the Elliptic Curve [RFC6954] Merkle, J. and M. Lochter, "Using the Elliptic Curve
Cryptography (ECC) Brainpool Curves for the Internet Key Cryptography (ECC) Brainpool Curves for the Internet Key
Exchange Protocol Version 2 (IKEv2)", RFC 6954, July 2013. Exchange Protocol Version 2 (IKEv2)", RFC 6954, July 2013.
Appendix A. Numerical Example for Curve25519 Appendix A. Numerical Example for Curve25519
Suppose we have both the initiator and the responder generating Suppose we have both the initiator and the responder generating
private keys by generating 32 random octets. As usual in IKEv2 and private keys by generating 32 random octets. As usual in IKEv2 and
its extension, we will denote Initiator values with the suffix _i and its extension, we will denote Initiator values with the suffix _i and
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