IPSec Working Group J. Solinas, NSA
INTERNET-DRAFT
Expires November 27, 2005 May 27, 2005
IKEv2 Authentication Using ECDSA
<draft-ietf-ipsec-ikev2-auth-ecdsa-01.txt>
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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 protocol, version 2 (IKEv2). 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 IKEv2
without introducing any changes to existing IKEv2 operation.
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1. Introduction
The Internet Key Exchange version 2, or IKEv2 [IKEv2], is a key
agreement and security negotiation protocol; it is used for key
establishment in IPSec. In the authentication exchange IKE_AUTH of
IKEv2, both parties must authenticate each other using a negotiated
authentication method. The defined methods are as follows:
RSA Digital Signature 1
Shared Key Message Integrity Code 2
DSS Digital Signature 3
The numbers corresponding to each method are used to identify the
method in the authentication payload ([IKEv2], sect. 3.8). This
draft defines a fourth option:
ECDSA Digital Signature 4
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 IKEv2
authentication and using elliptic curve groups for the IKEv2 key
exchange. Implementers of IPSec and IKEv2 may therefore find it
desirable to use ECDSA as the IKE_AUTH authentication method.
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. ECDSA
The Elliptic Curve Digital Signature Algorithm (ECDSA) is the
elliptic curve analogue of the DSA (DSS) signature method [DSS].
It is defined in the ANSI X9.62 standard [X9.62]. Other compatible
specifications include FIPS 186-2 [DSS], IEEE 1363 [IEEE-1363],
IEEE 1363A [IEEE-1363A], and SEC1 [SEC1].
Like DSA, ECDSA incorporates the use of a hash function. [SHS]
specifies hash functions that are appropriate for use with ECDSA.
Implementations of IKEv2 using ECDSA SHOULD use one of these hash
functions.
ECDSA signatures are smaller than RSA signatures of similar
cryptographic strength. 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 more quickly than similar strength RSA
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or DSA operations (see [LV] for a security analysis of key sizes
across public key algorithms). These advantages of signature size,
bandwidth, and computational efficiency may make ECDSA an
attractive choice for many IKE implementations.
Recommended elliptic curve domain parameters for use with ECDSA are
given in FIPS 186-2 [DSS], ANSI X9.62 [X9.62], and SEC 2 [SEC2].
Implementations of IKEv2 using ECDSA MAY use one of these domain
parameters. A subset of these parameters are recommended in
[IKEv2-ECC] for use in the IKEv2 key exchange. These parameters
MAY be used for ECDSA as well.
3. Specifying ECDSA within IKEv2
The sequence of IKE_AUTH message payloads is the same with ECDSA
signatures as with DSS or RSA signatures.
When ECDSA is used in IKEv2, 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
[X9.62].
As with 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 if the public keys of
the parties are not already known to each other. The use of
Internet X.509 public key infrastructure certificates [RFC-3280] is
recommended; the representation of ECDSA keys in X.509 certificates
is specified in [RFC-3279]. This representation SHOULD be used if
X.509 certificates are used. The certificates MAY be exchanged as
part of the IKE_AUTH exchange (see [IKEv2], sect. 2.15).
Implemententers may find it convenient, when using ECDSA as the
authentication method, to specify the hash used by ECDSA as the value
of the hash algorithm attribute. Implementers may also find it
convenient to use ECDSA authentication in conjunction with an
elliptic curve group for the IKEv2 Diffie-Hellman key agreement; see
[IKEv2-ECC] for some specific curves for the key agreement.
4. Security Considerations
Implementors should ensure that appropriate security measures are in
place when they deploy ECDSA within IKEv2. 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 [X9.62], FIPS 186-2 [DSS], and SEC 2
[SEC2].
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5. IANA Considerations
This document has no actions for IANA.
6. References
6.1 Normative
[IKEv2] C. Kaufman, Internet Key Exchange (IKEv2) Protocol, 2004,
http://www.ietf.org/internet-drafts/draft-ietf-ipsec-ikev2-17.txt
[X9.62] American National Standards Institute, ANS X9.62-1998:
Public Key Cryptography for the Financial Services Industry: The
Elliptic Curve Digital Signature Algorithm. January 1999.
6.2 Informative
[DSS] U.S. Department of Commerce/National Institute of Standards
and Technology, Digital Signature Standard (DSS), FIPS PUB 186-2,
January 2000. (http://csrc.nist.gov/publications/fips/index.html)
[IANA] Internet Assigned Numbers Authority, Internet Key Exchange
(IKE) Attributes. (http://www.iana.org/assignments/ipsec-registry)
[IEEE-1363] Institute of Electrical and Electronics Engineers.
IEEE 1363-2000, Standard for Public Key Cryptography.
(http://grouper.ieee.org/groups/1363/index.html)
[IEEE-1363A] Institute of Electrical and Electronics Engineers.
IEEE 1363A-2004, Standard for Public Key Cryptography -
Amendment 1: Additional Techniques.
(http://grouper.ieee.org/groups/1363/index.html)
[IKEv2-ECC] J. Solinas, ECC Groups For IKEv2, 2005.
(draft-ietf-ipsec-ikev2-ecc-groups-01.txt)
[LV] A. Lenstra and E. Verheul, "Selecting Cryptographic Key
Sizes", Journal of Cryptology 14 (2001), pp. 255-293.
[RFC-3279] Bassham, L., Housley, R., and Polk, W., RFC 3279,
Algorithms and Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List (CRL)
Profile, 2002. (http://www.ietf.org/rfc/rfc3279.txt)
[RFC-3280] Housley, R., Polk, W., Ford, W. and D. Solo, RFC 3280,
Internet X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile, 2002.
(http://www.ietf.org/rfc/rfc3279.txt)
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[SEC1] Standards for Efficient Cryptography Group. SEC 1 - Elliptic
Curve Cryptography, v. 1.0, 2000. (http://www.secg.org)
[SEC2] Standards for Efficient Cryptography Group. SEC 2 -
Recommended Elliptic Curve Domain Parameters, v. 1.0, 2000.
(http://www.secg.org)
[SHS] FIPS 180-2, "Secure Hash Standard", National Institute of
Standards and Technology, 2002.
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7. Author's Address
Jerome A. Solinas
National Security Agency
jasolin@orion.ncsc.mil
Comments are solicited and should be addressed to the author.
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