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Network Working Group                                         P. Hoffman
Internet-Draft                                            VPN Consortium
Intended status: Standards Track                        January 25, 2010
Expires: July 29, 2010


                     Elliptic Curve DSA for DNSSEC
                     draft-hoffman-dnssec-ecdsa-01

Abstract

   This document describes how to specify Elliptic Curve DSA keys and
   signatures in DNSSEC.  It lists curves of different sizes, and uses
   the SHA-2 family of hashes for signatures.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 29, 2010.

Copyright Notice

   Copyright (c) 2010 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
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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   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 BSD License.

   This document may contain material from IETF Documents or IETF
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   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.


1.  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
   1024 or 2048 bits long.

   This document defines the DNSKEY and RRSIG resource records (RRs) of
   three new signing algorithms: ECDSA with curve P-224 and SHA-256,
   ECDSA with curve P-256 and SHA-256, and ECDSA with curve P-384 and
   SHA-384.  It 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].

   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.

   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



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   5430 [RFC5430].

   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].


2.  SHA-384 DS Records

   SHA-384 is defined in FIPS 180-3 [FIPS-180-3] and RFC 4634 [RFC4634],
   and is similar to SHA-256 in many ways.  The implementation of SHA-
   384 in DNSSEC follows the implementation of SHA-256 as specified in
   RFC 4509 except that the underlying algorithm is SHA-384, the digest
   value is 48 bytes long, and the digest type code is {TBA-1}.


3.  ECDSA Parameters

   Verifying ECDSA signatures requires agreement between the signer and
   the verifier of the parameters used.  FIPS 186-3 [FIPS-186-3] lists
   some NIST-recommended elliptic curves.  These are the same curves as
   listed in RFC 5114 [RFC5114].  The curves used in this document are:

   FIPS 186-3                  RFC 5114
   ------------------------------------------------------------------
   P-224 (Section D.1.2.2)     224-bit Random ECP Group (Section 2.5)
   P-256 (Section D.1.2.3)     256-bit Random ECP Group (Section 2.6)
   P-384 (Section D.1.2.4)     384-bit Random ECP Group (Section 2.7)


4.  DNSKEY and RRSIG Resource Records for ECDSA

   ECDSA public keys consist of a single value, called "Q" in FIPS
   186-3.  In DNSSEC keys, Q is a simple bit string that represents the
   uncompressed form of a curve point.

   The ECDSA signature is the combination of two non-negative integers,
   called "r" and "s" in FIPS 186-3.  The two integers, each of which is
   formatted as a simple bit string, are combined into a single longer
   bit string for DNSSEC as the concatenation "r | s".

   The algorithm numbers associated with the DNSKEY and RRSIG resource
   records are fully defined in the IANA Considerations section.  They
   are:

   o  DNSKEY and RRSIG RRs signifying ECDSA with the P-224 curve and
      SHA-256 use the algorithm number {TBA-2}.




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   o  DNSKEY and RRSIG RRs signifying ECDSA with the P-256 curve and
      SHA-256 use the algorithm number {TBA-3}.

   o  DNSKEY and RRSIG RRs signifying ECDSA with the P-384 curve and
      SHA-384 use the algorithm number {TBA-4}.

   Conformant implementations MUST support signing and/or validation of
   signatures with both ECDSA with the P-256 curve and SHA-256, and with
   ECDSA with the P-384 curve and SHA-384.  (ECDSA with the P-224 curve
   and SHA-256 is defined here for systems that want to have a strength
   equivalence of RSA with 2048-bit keys, but is not required for
   conformance.)


5.  Support for NSEC3 Denial of Existence

   RFC 5155 [RFC5155] defines new algorithm identifiers for existing
   signing algorithms, to indicate that zones signed with these
   algorithm identifiers can use NSEC3 as well as NSEC records to
   provide denial of existence.  That mechanism was chosen to protect
   implementations predating RFC 5155 from encountering resource records
   they could not know about.  This document does not define such
   algorithm aliases.

   A DNSSEC validator that implements the signing algorithms defined in
   this document MUST be able to validate negative answers in the form
   of both NSEC and NSEC3 with hash algorithm 1, as defined in RFC 5155.
   An authoritative server that does not implement NSEC3 MAY still serve
   zones that use the signing algorithms defined in this document with
   NSEC denial of existence.


6.  Examples

   [[ To be filled in later. ]]


7.  IANA Considerations

   This document updates the IANA registry for digest types in DS
   records, currently called "Delegation Signer Resource Record, Digest
   Algorithms".  The following entry is added:

   Value          {TBA-1}
   Digest Type    SHA-384
   Status         OPTIONAL

   This document updates the IANA registry "Domain Name System Security



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   (DNSSEC) Algorithm Numbers".  The following three entries are added
   to the registry:

   Number         {TBA-2}
   Description    ECDSA Curve P-224 with SHA-256
   Mnemonic       ECDSAP224SHA256
   Zone Signing   Y
   Trans. Sec.    *
   Reference      This document

   Number         {TBA-3}
   Description    ECDSA Curve P-256 with SHA-256
   Mnemonic       ECDSAP256SHA256
   Zone Signing   Y
   Trans. Sec.    *
   Reference      This document

   Number         {TBA-4}
   Description    ECDSA Curve P-384 with SHA-384
   Mnemonic       ECDSAP384SHA384
   Zone Signing   Y
   Trans. Sec.    *
   Reference      This document

   * There has been no determination of standardization of the
     use of this algorithm with Transaction Security.


8.  Security Considerations

   The cryptographic strength of ECDSA with curve P-224, P-256 or P-384
   is generally considered to be equivalent to half the size of the key,
   or 112 bits, 128 bits, and 192 bits, respectively.  Such an
   assessment could, of course, change in the future if new attacks that
   work better than the ones known today are found.


9.  References

9.1.  Normative References

   [FIPS-180-3]
              National Institute of Standards and Technology, U.S.
              Department of Commerce, "Secure Hash Standard (SHS)",
              FIPS 180-3, October 2008.

   [FIPS-186-3]
              National Institute of Standards and Technology, U.S.



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              Department of Commerce, "Digital Signature Standard",
              FIPS 186-3, June 2009.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

   [RFC4509]  Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer
              (DS) Resource Records (RRs)", RFC 4509, May 2006.

   [RFC5114]  Lepinski, M. and S. Kent, "Additional Diffie-Hellman
              Groups for Use with IETF Standards", RFC 5114,
              January 2008.

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, March 2008.

9.2.  Informative References

   [RFC4634]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and HMAC-SHA)", RFC 4634, July 2006.

   [RFC5430]  Salter, M., Rescorla, E., and R. Housley, "Suite B Profile
              for Transport Layer Security (TLS)", RFC 5430, March 2009.


Appendix A.  Change History

   This entire section should be removed before publication as an RFC.

A.1.  Changes betweeen draft-hoffman-dnssec-ecdsa-00 and -01

   Numerous editorial fixes from Alfred Hoenes.

   In the IANA Considerations, used the same wording about TSIG as is
   used in draft-ietf-dnsext-dnssec-rsasha256-14: "There has been no



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   determination of standardization of the use of this algorithm with
   Transaction Security."


Author's Address

   Paul Hoffman
   VPN Consortium

   Email: paul.hoffman@vpnc.org









































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