IPSec Working Group S. Blake-Wilson and P. Fahn
INTERNET-DRAFT Certicom Corp.
Expires: September 14, 2001 March 15, 2001
IKE Authentication Using ECDSA
<draft-ietf-ipsec-ike-auth-ecdsa-02.txt>
Status of this Memo
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Abstract
This document describes how the Elliptic Curve Digital Signature
Algorithm (ECDSA) may be used as the authentication method within
the Internet Key Exchange (IKE) protocol. ECDSA may provide
benefits including computational efficiency, small signature sizes,
and minimal bandwidth, compared to other available digital signature
methods. This document adds ECDSA capability to IKE without
introducing any changes to existing IKE operation.
Table of Contents
1. Introduction ................................................. 2
2. ECDSA ........................................................ 2
3. Specifying ECDSA within IKE .................................. 3
4. Security Considerations ...................................... 4
5. Intellectual Property Rights ................................. 4
6. Acknowledgments .............................................. 4
7. References ................................................... 5
8. Authors' Addresses ........................................... 6
9. Full Copyright Statement ..................................... 6
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1. Introduction
The Internet Key Exchange, or IKE [RFC2409], is a key agreement
and security negotiation protocol; it is used for key establishment in
IPSec. In Phase 1 of IKE, both parties must authenticate each other
using a negotiated authentication method. One option for the
authentication method is digital signatures using public key
cryptography. Currently, there are two digital signature methods
defined for use within Phase 1: RSA signatures and DSA (DSS)
signatures. This document introduces ECDSA signatures as a third
method.
For any given level of security against the best attacks known, ECDSA
signatures are smaller than RSA signatures and ECDSA keys require less
bandwidth than DSA keys; there are also advantages of computational
speed and efficiency in many settings. Additional efficiency may be
gained by simultaneously using ECDSA for IKE authentication and using
elliptic curve groups for the IKE key exchange. Implementers of IPSec
and IKE may therefore find it desirable to use ECDSA as the Phase 1
authentication method.
2. ECDSA
The Elliptic Curve Digital Signature Algorithm (ECDSA) is the elliptic
curve analogue of the DSA (also called DSS) signature method
[FIPS186-2]. The Elliptic Curve Digital Signature Algorithm (ECDSA) is
defined in the ANSI X9.62 standard [ANSIX962]; compatible
specifications include FIPS 186-2 [FIPS186-2], IEEE P1363 [IEEEP1363],
and SEC 1 [SEC1]. The use of ECDSA in X.509 certificates is described
in IETF PKIX [PKIX-ALG].
ECDSA signatures are smaller than RSA signatures of similar
cryptographic strength; see [KEYS] for a security analysis of key
sizes across public key algorithms. ECDSA public keys (and
certificates) are smaller than similar strength DSA keys, resulting in
improved communications efficiency. Furthermore, on many platforms
ECDSA operations can be computed faster than similar strength RSA or
DSA operations. These advantages of signature size, bandwidth, and
computational efficiency make ECDSA an attractive choice for many IKE
implementions.
Recommended elliptic curve domain parameters for use with ECDSA are
given in FIPS 186-2 [FIPS186-2] and SEC 2 [SEC2]. A subset of these
parameters are recommended in [ECC-GR] for use in the IKE key exchange.
Like DSA, ECDSA incorporates the use of a hash function; currently,
the only hash function defined for use with ECDSA is the SHA-1 message
digest algorithm [FIPS180-1].
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3. Specifying ECDSA within IKE
The IKE key negotiation protocol consists of two phases, Phase 1 and
Phase 2. Within Phase 1, the two negotiating parties authenticate each
other, using either pre-shared keys, digital signatures, or public-key
encryption. For digital signatures and public-key encryption methods,
there are multiple options. The authentication method is specified as
an attribute in the negotiated Phase 1 Security Association (SA).
Until now, there have been a total of seven specific authentication
methods in Phase 1. We now add an eighth option: ECDSA signatures,
specified by attribute value 8 in the SA. The new list of
IANA-assigned attribute numbers for Phase 1 authentication is:
- Authentication Method
pre-shared key 1
DSS signatures 2
RSA signatures 3
Encryption with RSA 4
Revised encryption with RSA 5
Encryption with El-Gamal 6
Revised encryption with El-Gamal 7
ECDSA signatures 8
values 9-65000 are reserved to IANA. Values 65001-65535 are for
private use among mutually consenting parties.
Phase 1 can be either Main Mode or Agressive Mode. The use and
specification of ECDSA signatures as the authentication method applies
to both modes. The sequence of Phase 1 message payloads is the same
with ECDSA signatures as with DSS or RSA signatures.
When ECDSA is used in IKE, the signature payload shall contain an
encoding of the computed signature, consisting of a pair of integers r
and s, encoded as a byte string using the ASN.1 syntax
"ECDSA-Sig-Value" with DER encoding rules as specified in
ANSI X9.62 [ANSIX962].
Note also that, like the other digital signature methods, ECDSA
authentication requires the parties to know and trust each other's
public key. This can be done by exchanging certificates, possibly
within the Phase 1 negotiation, if the public keys of the parties are
not already known to each other. The use of Internet X.509 public key
infrastructure certificates [PKIX-CERT] is recommended; the
representation of ECDSA keys in X.509 certificates is specified in
[PKIX-ALG].
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Since ECDSA requires the use of the SHA-1 hash function,
implemententers may find it convenient to specify SHA-1 as the value
of the hash algorithm attribute when using ECDSA as the authentication
method. Implementers may also find it convenient to use ECDSA
authentication in conjunction with an elliptic curve group for the IKE
Diffie-Hellman key agreement; see [ECC-GR] for specific curves for the
key agreement.
4. Security Considerations
Implementors should ensure that appropriate security measures are in
place when they deploy ECDSA within IKE. In particular, the security
of ECDSA requires the careful selection of both key sizes and elliptic
curve domain parameters. Selection guidelines for these parameters and
some specific recommended curves that are considered safe are provided
in ANSI X9.62 [ANSIX962], FIPS 186-2 [FIPS186-2], and SEC 2 [SEC2].
5. Intellectual Property Rights
The IETF has been notified of intellectual property rights claimed in
regard to the specification contained in this document. For more
information, consult the online list of claimed rights
(http://www.ietf.org/ipr.html).
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to pertain
to the implementation or use of the technology described in this
document or the extent to which any license under such rights might or
might not be available; neither does it represent that it has made any
effort to identify any such rights. Information on the IETF's
procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such proprietary
rights by implementors or users of this specification can be obtained
from the IETF Secretariat.
6. Acknowledgments
The authors would like to thank Paul Lambert and Prakash Panjwani for
their comments and suggestions.
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7. References
[ANSIX962] ANSI X9.62-1999, "Public Key Cryptography For The Financial
Services Industry: The Elliptic Curve Digital Signature
Algorithm (ECDSA)", Americal National Standards Institute,
1998.
[ECC-GR] S. Blake-Wilson, M. Salter, and Y. Poeluev, "Additional
ECC Groups for IKE", IPSEC Working Group Internet-Draft
draft-ietf-ipsec-ike-ecc-groups-03.txt. September 1999.
[FIPS180-1] FIPS 180-1, "Secure Hash Standard", National Institute of
Standards and Technology, 1995.
[FIPS186-2] FIPS 186-2, "Digital Signature Standard", National Institute
of Standards and Technology, 2000.
[IEEEP1363] IEEE P1363, "Standard Specifications for Public Key
Cryptography", Institute of Electrical and Electronics
Engineers, 2000.
[KEYS] A. Lenstra and E. Verheul, "Selecting Cryptographic Key
Sizes", October 1999. Presented at Public Key Cryptography
Conference, Melbourne, Australia, January 2000. Available
at <http://www.cryptosavvy.com/>.
[PKIX-ALG] L. Bassham, R. Housley and W. Polk, "Algorithms and
Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and CRL Profile", PKIX Working
Group Internet-Draft, draft-ietf-pkix-ipki-pkalgs-02.txt,
March 2001.
[PKIX-CERT] W. Ford, R. Housley, W. Polk and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and CRL Profile", PKIX
Working Group Internet-Draft,
draft-ietf-pkix-new-part1-05.txt, March 2001.
[RFC2409] D. Harkins and D. Carrel, "The Internet Key Exchange",
IETF RFC 2409, November 1998.
[SEC1] SEC 1, "Elliptic Curve Cryptography", Standards for Efficient
Cryptography Group, 2000.
[SEC2] SEC 2, "Recommended Elliptic Curve Domain Parameters",
Standards for Efficient Cryptography Group, 2000.
Blake-Wilson, Fahn [Page 5]
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8. Author's Address
Simon Blake-Wilson
Certicom Corp.
sblake-wilson@certicom.com
Paul Fahn
Certicom Corp.
pfahn@certicom.com
9. Full Copyright Statement
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