Internet Engineering Task Force (IETF) P. Hoffman
Request for Comments: 6605 VPN Consortium
Category: Standards Track W.C.A. Wijngaards
ISSN: 2070-1721 NLnet Labs
Elliptic Curve Digital Signature Algorithm (DSA) for DNSSEC
This document describes how to specify Elliptic Curve Digital
Signature Algorithm (DSA) keys and signatures in DNS Security
(DNSSEC). It lists curves of different sizes and uses the SHA-2
family of hashes for signatures.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Hoffman & Wijngaards Standards Track [Page 1]RFC 6605 ECDSA for DNSSEC April 20121. Introduction
DNSSEC, which is broadly defined in RFCs 4033, 4034, and 4035
([RFC4033], [RFC4034], and [RFC4035]), uses cryptographic keys and
digital signatures to provide authentication of DNS data. Currently,
the most popular signature algorithm is RSA with SHA-1, using keys
that are 1024 or 2048 bits long.
This document defines the DNSKEY and RRSIG resource records (RRs) of
two new signing algorithms: ECDSA (Elliptic Curve DSA) with curve
P-256 and SHA-256, and ECDSA with curve P-384 and SHA-384. (A
description of ECDSA can be found in [FIPS-186-3].) This document
also defines the DS RR for the SHA-384 one-way hash algorithm; the
associated DS RR for SHA-256 is already defined in RFC 4509
[RFC4509]. [RFC6090] provides a good introduction to implementing
Current estimates are that ECDSA with curve P-256 has an approximate
equivalent strength to RSA with 3072-bit keys. Using ECDSA with
curve P-256 in DNSSEC has some advantages and disadvantages relative
to using RSA with SHA-256 and with 3072-bit keys. ECDSA keys are
much shorter than RSA keys; at this size, the difference is 256
versus 3072 bits. Similarly, ECDSA signatures are much shorter than
RSA signatures. This is relevant because DNSSEC stores and transmits
both keys and signatures.
In the two signing algorithms defined in this document, the size of
the key for the elliptic curve is matched with the size of the output
of the hash algorithm. This design is based on the widespread belief
that the equivalent strength of P-256 and P-384 is half the length of
the key, and also that the equivalent strength of SHA-256 and SHA-384
is half the length of the key. Using matched strengths prevents an
attacker from choosing the weaker half of a signature algorithm. For
example, in a signature that uses RSA with 2048-bit keys and SHA-256,
the signing portion is significantly weaker than the hash portion,
whereas the two algorithms here are balanced.
Signing with ECDSA is significantly faster than with RSA (over 20
times in some implementations). However, validating RSA signatures
is significantly faster than validating ECDSA signatures (about 5
times faster in some implementations).
Some of the material in this document is copied liberally from RFC
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 RFC 2119 [RFC2119].
Hoffman & Wijngaards Standards Track [Page 2]