--- 1/draft-ietf-dnsext-ds-sha256-04.txt 2006-02-23 22:12:15.000000000 +0100 +++ 2/draft-ietf-dnsext-ds-sha256-05.txt 2006-02-23 22:12:15.000000000 +0100 @@ -1,17 +1,17 @@ Network Working Group W. Hardaker Internet-Draft Sparta -Expires: July 17, 2006 January 13, 2006 +Expires: August 25, 2006 February 21, 2006 Use of SHA-256 in DNSSEC Delegation Signer (DS) Resource Records (RRs) - draft-ietf-dnsext-ds-sha256-04.txt + draft-ietf-dnsext-ds-sha256-05.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that @@ -22,21 +22,21 @@ and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. - This Internet-Draft will expire on July 17, 2006. + This Internet-Draft will expire on August 25, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document specifies how to use the SHA-256 digest type in DNS Delegation Signer (DS) Resource Records (RRs). DS records, when stored in a parent zone, point to key signing DNSKEY key(s) in a @@ -49,43 +49,47 @@ 2.1. DS record field values . . . . . . . . . . . . . . . . . . 3 2.2. DS Record with SHA-256 Wire Format . . . . . . . . . . . . 3 2.3. Example DS Record Using SHA-256 . . . . . . . . . . . . . . 4 3. Implementation Requirements . . . . . . . . . . . . . . . . . . 4 4. Deployment Considerations . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6.1. Potential Digest Type Downgrade Attacks . . . . . . . . . . 5 6.2. SHA-1 vs SHA-256 Considerations for DS Records . . . . . . 6 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6 - 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 8.1. Normative References . . . . . . . . . . . . . . . . . . . 6 + 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 8.1. Normative References . . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . . . 9 1. Introduction The DNSSEC [RFC4033] [RFC4034] [RFC4035] DS RR is published in parent zones to distribute a cryptographic digest of a child's Key Signing Key (KSK) DNSKEY RR. The DS RRset is signed by at least one of the parent zone's private zone data signing keys for each algorithm in use by the parent. Each signature is published in an RRSIG resource record, owned by the same domain as the DS RRset and with a type covered of DS. + 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. Implementing the SHA-256 algorithm for DS record support This document specifies that the digest type code [XXX: To be - assigned by IANA; likely 2] is to be assigned to SHA-256 [SHA256] for - use within DS records. The results of the digest algorithm MUST NOT - be truncated and the entire 32 byte digest result is to be published - in the DS record. + assigned by IANA; likely 2] is to be assigned to SHA-256 [SHA256] + [SHA256CODE] for use within DS records. The results of the digest + algorithm MUST NOT be truncated and the entire 32 byte digest result + is to be published in the DS record. 2.1. DS record field values Using the SHA-256 digest algorithm within a DS record will make use of the following DS-record fields: Digest type: [XXX: To be assigned by IANA; likely 2] Digest: A SHA-256 bit digest value calculated by using the following formula ("|" denotes concatenation). The resulting value is not @@ -160,20 +164,22 @@ Because zone administrators can not control the deployment speed of support for SHA-256 in validators that may be referencing any of their zones, zone operators should consider deploying both SHA-1 and SHA-256 based DS records. This should be done for every DNSKEY for which DS records are being generated. Whether to make use of both digest types and for how long is a policy decision that extends beyond the scope of this document. 5. IANA Considerations + Only one IANA action is required by this document: + The Digest Type to be used for supporting SHA-256 within DS records needs to be assigned by IANA. This document requests that the Digest Type value of 2 be assigned to the SHA-256 digest algorithm. At the time of this writing, the current digest types assigned for use in DS records are as follows: VALUE Digest Type Status 0 Reserved - 1 SHA-1 MANDATORY @@ -203,77 +209,85 @@ o The DS record with the SHA-256 digest fails to match the digest computed using the child zone's DNSKEY. Then if the validator accepts the above situation as secure then this can be used as a downgrade attack since the stronger SHA-256 digest is ignored. 6.2. SHA-1 vs SHA-256 Considerations for DS Records - Because of the weaknesses recently discovered within the SHA-1 - algorithm, users of DNSSEC are encouraged to deploy the use of SHA- - 256 as soon as the software implementations in use allow for it. + Users of DNSSEC are encouraged to deploy SHA-256 as soon as software + implementations allow for it. SHA-256 is widely believed to be more + resilient to attack than SHA-1, and confidence in SHA-1's strength is + being eroded by recently-announced attacks. Regardless of whether or + not the attacks on SHA-1 will affect DNSSEC, it is believed (at the + time of this writing) that SHA-256 is the better choice for use in DS + records. At the time of this publication, the SHA-256 digest algorithm is considered sufficiently strong for the immediate future. It is also considered sufficient for use in DNSSEC DS RRs for the immediate future. However, future published attacks may weaken the usability of this algorithm within the DS RRs. It is beyond the scope of this document to speculate extensively on the cryptographic strength of the SHA-256 digest algorithm. Likewise, it is also beyond the scope of this document to specify whether or for how long SHA-1 based DS records should be simultaneously published alongside SHA-256 based DS records. 7. Acknowledgments This document is a minor extension to the existing DNSSEC documents and those authors are gratefully appreciated for the hard work that went into the base documents. The following people contributed to portions of this document in some - fashion: Mark Andrews, Roy Arends, Olafur Gudmundsson, Olaf M. - Kolkman, Edward Lewis, Scott Rose, Stuart E. Schechter, Sam Weiler. + fashion: Mark Andrews, Roy Arends, Olafur Gudmundsson, Paul Hoffman, + Olaf M. Kolkman, Edward Lewis, Scott Rose, Stuart E. Schechter, Sam + Weiler. 8. References 8.1. Normative References + [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. [SHA256] National Institute of Standards and Technology, "Secure Hash Algorithm. NIST FIPS 180-2", August 2002. 8.2. Informative References [SHA256CODE] - Motorola Labs, "US Secure Hash Algorithms (SHA)", + Eastlake, D., "US Secure Hash Algorithms (SHA)", June 2005. Author's Address Wes Hardaker Sparta P.O. Box 382 - Davis 95617 + Davis, CA 95617 US Email: hardaker@tislabs.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights 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