draft-ietf-ipsecme-safecurves-01.txt   draft-ietf-ipsecme-safecurves-02.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: August 5, 2016 SJD Expires: February 6, 2017 SJD
February 2, 2016 August 5, 2016
Curve25519 and Curve448 for IKEv2 Key Agreement Curve25519 and Curve448 for IKEv2 Key Agreement
draft-ietf-ipsecme-safecurves-01 draft-ietf-ipsecme-safecurves-02
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
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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 August 5, 2016. This Internet-Draft will expire on February 6, 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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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 . . . . . . . . . . . . . . . . . . . . . . 4 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
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 Appendix A. Numerical Example for Curve25519 . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
[RFC7748] describes two elliptic curves: Curve25519 and Curve448, as The "Elliptic Curves for Security" document [RFC7748] describes two
well as the X25519 and X448 functions for performing key agreement elliptic curves: Curve25519 and Curve448, as well as the X25519 and
(Diffie-Hellman) operations with these curves. The curves and X448 functions for performing key agreement (Diffie-Hellman)
functions are designed for both performance and security. operations with these curves. The curves and functions are designed
for both performance and security.
Almost ten years ago [RFC4753] specified the first elliptic curve Almost ten years ago the "ECP Groups for IKE and IKEv2" document
Diffie-Hellman groups for the Internet Key Exchange protocol (IKEv2 - [RFC4753] specified the first elliptic curve Diffie-Hellman groups
[RFC7296]). These were the so-called NIST curves. The state of the for the Internet Key Exchange protocol (IKEv2 - [RFC7296]). These
art has advanced since then. More modern curves allow faster were the so-called NIST curves. The state of the art has advanced
implementations while making it much easier to write constant-time since then. More modern curves allow faster implementations while
implementations free from time-based side-channel attacks. This making it much easier to write constant-time implementations free
document defines two such curves for use in IKE. See [Curve25519] from time-based side-channel attacks. This document defines two such
for details about the speed and security of the Curve25519 function. 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 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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SHARED_SECRET = X(d, pub_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. The value xx is used an IKE_SA_INIT or a CREATE_CHILD_SA exchange. The value TBA1 is used
for the group defined by Curve25519 and yy is used for the group for the group defined by Curve25519 and the value TBA2 is used for
defined by Curve448. Both are TBA by IANA. the group defined by Curve448.
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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| Diffie-Hellman Group Num | RESERVED | | Diffie-Hellman Group Num | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ 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 TBA1 for Curve25519, or TBA2 for
Curve448 (both TBA by IANA). Curve448.
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 [RFC7748] section 6 of [RFC7748]
3.2. Recipient Tests 3.2. Recipient Tests
This document matches the discussion in [RFC7748] 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 [RFC7748] for further discussion. canonical values. See section 5 of [RFC7748] for further discussion.
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"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 the parameters for Curve25519 was designed by D. J. Bernstein and the parameters for
Curve448 ("Goldilocks") is by Mike Hamburg. The specification of Curve448 ("Goldilocks") is by Mike Hamburg. The specification of
algorithms, wire format and other considerations are in RFC 7748 by algorithms, wire format and other considerations are in RFC 7748 by
Adam Langley, Mike Hamburg, and Sean Turner. Adam Langley, Mike Hamburg, and Sean Turner.
The examples in Appendix A were calculated using the master version
of OpenSSL, retrieved on August 4th, 2016.
7. References 7. References
7.1. Normative References 7.1. Normative References
[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.
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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", [RFC4753] Fu, D. and J. Solinas, "ECP Groups For IKE and IKEv2",
RFC 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 Appendix A. Numerical Example for Curve25519
Suppose we have both the initiator and the responder generating
private keys by generating 32 random octets. As usual in IKEv2 and
its extension, we will denote Initiator values with the suffix _i and
responder values with the suffix _r:
random_i = 75 1f b4 30 86 55 b4 76 b6 78 9b 73 25 f9 ea 8c
dd d1 6a 58 53 3f f6 d9 e6 00 09 46 4a 5f 9d 94
random_r = 0a 54 64 52 53 29 0d 60 dd ad d0 e0 30 ba cd 9e
55 01 ef dc 22 07 55 a1 e9 78 f1 b8 39 a0 56 88
These numbers need to be fixed by unsetting some bits as described in
section 5 of RFC 7748. This affects only the first and last octets
of each value:
fixed_i = 70 1f b4 30 86 55 b4 76 b6 78 9b 73 25 f9 ea 8c
dd d1 6a 58 53 3f f6 d9 e6 00 09 46 4a 5f 9d 54
fixed_r = 08 54 64 52 53 29 0d 60 dd ad d0 e0 30 ba cd 9e
55 01 ef dc 22 07 55 a1 e9 78 f1 b8 39 a0 56 48
The actual private keys are considered to be encoded in little-endian
format:
d_i = 549D5F4A460900E6D9F63F53586AD1DD8CEAF925739B78B676B4558630B41F70
d_r = 4856A039B8F178E9A1550722DCEF01559ECDBA30E0D0ADDD600D295352645408
The public keys are generated from this using the formula in
Section 2:
pub_i = X25519(d_i, G) =
48 d5 dd d4 06 12 57 ba 16 6f a3 f9 bb db 74 f1
a4 e8 1c 08 93 84 fa 77 f7 90 70 9f 0d fb c7 66
pub_r = X25519(d_r, G) =
0b e7 c1 f5 aa d8 7d 7e 44 86 62 67 32 98 a4 43
47 8b 85 97 45 17 9e af 56 4c 79 c0 ef 6e ee 25
And this is the value of the Key Exchange Data field in the key
exchange payload described in Section 3.1. The shared value is
calculated as in Section 2:
SHARED_SECRET = X25519(d_i, pub_r) = X25519(d_r, pub_i) =
c7 49 50 60 7a 12 32 7f-32 04 d9 4b 68 25 bf b0
68 b7 f8 31 9a 9e 37 08-ed 3d 43 ce 81 30 c9 50
Authors' Addresses
Yoav Nir Yoav Nir
Check Point Software Technologies Ltd. Check Point Software Technologies Ltd.
5 Hasolelim st. 5 Hasolelim st.
Tel Aviv 6789735 Tel Aviv 6789735
Israel Israel
Email: ynir.ietf@gmail.com Email: ynir.ietf@gmail.com
Simon Josefsson Simon Josefsson
SJD AB SJD AB
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