draft-ietf-ipsecme-safecurves-00.txt   draft-ietf-ipsecme-safecurves-01.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: March 11, 2016 SJD Expires: August 5, 2016 SJD
September 8, 2015 February 2, 2016
Curve25519 and Curve448 for IKEv2 Key Agreement Curve25519 and Curve448 for IKEv2 Key Agreement
draft-ietf-ipsecme-safecurves-00 draft-ietf-ipsecme-safecurves-01
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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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 March 11, 2016. This Internet-Draft will expire on August 5, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . 2 1.1. Conventions Used in This Document . . . . . . . . . . . . 2
2. Curve25519 & Curve448 . . . . . . . . . . . . . . . . . . . . 2 2. Curve25519 & Curve448 . . . . . . . . . . . . . . . . . . . . 2
3. Use and Negotiation in IKEv2 . . . . . . . . . . . . . . . . 3 3. Use and Negotiation in IKEv2 . . . . . . . . . . . . . . . . 3
3.1. Key Exchange Payload . . . . . . . . . . . . . . . . . . 3 3.1. Key Exchange Payload . . . . . . . . . . . . . . . . . . 3
3.2. Recipient Tests . . . . . . . . . . . . . . . . . . . . . 4 3.2. Recipient Tests . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction 1. Introduction
[CFRG-Curves] describes the two elliptic curves Curve25519 and [RFC7748] describes two elliptic curves: Curve25519 and Curve448, as
Curve448 and the X25519 and X448 functions for performing Diffie- well as the X25519 and X448 functions for performing key agreement
Hellman operations on the curves. The curves and functions are (Diffie-Hellman) operations with these curves. The curves and
designed with performance and security in mind. functions are designed for both performance and security.
Almost ten years ago [RFC4753] specified the first elliptic curve Almost ten years ago [RFC4753] specified the first elliptic curve
Diffie-Hellman groups for the Internet Key Exchange protocol (IKEv2 - Diffie-Hellman groups for the Internet Key Exchange protocol (IKEv2 -
[RFC7296]). These were the so-called NIST curves. The state of the [RFC7296]). These were the so-called NIST curves. The state of the
art has advanced since then. More modern curves allow faster art has advanced since then. More modern curves allow faster
implementations while making it much easier to write constant-time implementations while making it much easier to write constant-time
implementations free from side-channel attacks. This document implementations free from time-based side-channel attacks. This
defines such a curve for use in IKE. See [Curve25519] for details document defines two such curves for use in IKE. See [Curve25519]
about the speed and security of the Curve25519 function. for details about the speed 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
functions defined in [CFRG-Curves]. All related parameters (for functions defined in [RFC7748]. All related parameters (for example,
example, the base point) and the encoding (in particular, pruning the the base point) and the encoding (in particular, pruning the least/
least/most significant bits and use of little-endian encoding) are most significant bits and use of little-endian encoding) are
inherited from [CFRG-Curves]. inherited from [RFC7748].
An ephemeral Diffie-Hellman key exchange using Curve25519 or Curve448 An ephemeral Diffie-Hellman key exchange using Curve25519 or Curve448
goes as follows: Each party picks a secret key d uniformly at random goes as follows: Each party picks a secret key d uniformly at random
and computes the corresponding public key. "X" is used below to and computes the corresponding public key. "X" is used below to
denote either X25519 or X448: denote either X25519 or X448, and "G" is used to denote the
corresponding base point:
x_mine = X(d, G) pub_mine = X(d, G)
Parties exchange their public keys (see Section 3.1) and compute a Parties exchange their public keys (see Section 3.1) and compute a
shared secret: shared secret:
SHARED_SECRET = X(d, x_peer). SHARED_SECRET = X(d, pub_peer).
This shared secret is used directly as the value denoted g^ir in This shared secret is used directly as the value denoted g^ir in
section 2.14 of RFC 7296. It is 32 octets when Curve25519 is used, section 2.14 of RFC 7296. It is 32 octets when Curve25519 is used,
and 56 octets when Curve448 is used. and 56 octets when Curve448 is used.
3. Use and Negotiation in IKEv2 3. Use and Negotiation in IKEv2
The use of Curve25519 and Curve448 in IKEv2 is negotiated using a The use of Curve25519 and Curve448 in IKEv2 is negotiated using a
Transform Type 4 (Diffie-Hellman group) in the SA payload of either Transform Type 4 (Diffie-Hellman group) in the SA payload of either
an IKE_SA_INIT or a CREATE_CHILD_SA exchange. an IKE_SA_INIT or a CREATE_CHILD_SA exchange. The value xx is used
for the group defined by Curve25519 and yy is used for the group
defined by Curve448. Both are TBA by IANA.
3.1. Key Exchange Payload 3.1. Key Exchange Payload
The diagram for the Key Exchange Payload from section 3.4 of RFC 7296 The diagram for the Key Exchange Payload from section 3.4 of RFC 7296
is copied below for convenience: is copied below for convenience:
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Payload |C| RESERVED | Payload Length | | Next Payload |C| RESERVED | Payload Length |
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~ Key Exchange Data ~ ~ Key Exchange Data ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Payload Length - For Curve25519 the public key is 32 octets, so o Payload Length - For Curve25519 the public key is 32 octets, so
the Payload Length field will be 40, and for Curve448 the public the Payload Length field will be 40, and for Curve448 the public
key is 56 octets, so the Payload Length field will be 64. key is 56 octets, so the Payload Length field will be 64.
o The Diffie-Hellman Group Num is xx for Curve25519, or yy for o The Diffie-Hellman Group Num is xx for Curve25519, or yy for
Curve448 (both TBA by IANA). Curve448 (both TBA by IANA).
o The Key Exchange Data is the 32 or 56 octets as described in o The Key Exchange Data is the 32 or 56 octets as described in
section 6 of [CFRG-Curves] section 6 of [RFC7748]
3.2. Recipient Tests 3.2. Recipient Tests
This document match the discussion in [CFRG-Curves] related to This document matches the discussion in [RFC7748] related to
receiving and accepting incompatible point formats. In particular, receiving and accepting incompatible point formats. In particular,
receiving entities MUST mask the most-significant bit in the final receiving entities MUST mask the most-significant bit in the final
byte for X25519 (but not X448), and implementations MUST accept non- byte for X25519 (but not X448), and implementations MUST accept non-
canonical values. See section 5 of [CFRG-Curves] for further canonical values. See section 5 of [RFC7748] for further discussion.
discussion.
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.
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5. IANA Considerations 5. IANA Considerations
IANA is requested to assign two values from the IKEv2 "Transform Type IANA is requested to assign two values from the IKEv2 "Transform Type
4 - Diffie-Hellman Group Transform IDs" registry, with names 4 - Diffie-Hellman Group Transform IDs" registry, with names
"Curve25519" and "Curve448" and this document as reference. The "Curve25519" and "Curve448" and this document as reference. The
Recipient Tests field should also point to this document. Recipient Tests field should also point to this document.
6. Acknowledgements 6. Acknowledgements
Curve25519 was designed by D. J. Bernstein and Curve448 Curve25519 was designed by D. J. Bernstein and the parameters for
("Goldilocks") is by Mike Hamburg. The specification of algorithms, Curve448 ("Goldilocks") is by Mike Hamburg. The specification of
wire format and other considerations are due to the CFRG document. algorithms, wire format and other considerations are in RFC 7748 by
Adam Langley, Mike Hamburg, and Sean Turner.
7. References 7. References
7.1. Normative References 7.1. Normative References
[CFRG-Curves]
Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", draft-irtf-cfrg-curves-06 (work in
progress), August 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC7296] Kivinen, T., Kaufman, C., Hoffman, P., Nir, Y., and P. [RFC7296] Kivinen, T., Kaufman, C., Hoffman, P., Nir, Y., and P.
Eronen, "Internet Key Exchange Protocol Version 2 Eronen, "Internet Key Exchange Protocol Version 2
(IKEv2)", RFC 7296, October 2014. (IKEv2)", RFC 7296, October 2014.
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
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", RFC [RFC4753] Fu, D. and J. Solinas, "ECP Groups For IKE and IKEv2",
4753, January 2007. RFC 4753, January 2007.
[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.
Authors' Addresses Authors' Addresses
Yoav Nir Yoav Nir
Check Point Software Technologies Ltd. Check Point Software Technologies Ltd.
5 Hasolelim st. 5 Hasolelim st.
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