draft-ietf-dnsext-ds-sha256-02.txt		draft-ietf-dnsext-ds-sha256-03.txt
	Network Working Group W. Hardaker		Network Working Group W. Hardaker
	Internet-Draft Sparta		Internet-Draft Sparta
	Expires: June 12, 2006 December 9, 2005		Expires: July 10, 2006 January 6, 2006
	Use of SHA-256 in DNSSEC Delegation Signer (DS) Resource Records (RRs)		Use of SHA-256 in DNSSEC Delegation Signer (DS) Resource Records (RRs)
	draft-ietf-dnsext-ds-sha256-02.txt		draft-ietf-dnsext-ds-sha256-03.txt
	Status of this Memo		Status of this Memo
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	This Internet-Draft will expire on June 12, 2006.		This Internet-Draft will expire on July 10, 2006.
	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2005).		Copyright (C) The Internet Society (2006).
	Abstract		Abstract
	This document specifies how to use the SHA-256 digest type in DNS		This document specifies how to use the SHA-256 digest type in DNS
	Delegation Signer (DS) Resource Records (RRs). DS records, when		Delegation Signer (DS) Resource Records (RRs). DS records, when
	stored in a parent zone, point to key signing DNSKEY key(s) in a		stored in a parent zone, point to key signing DNSKEY key(s) in a
	child zone.		child zone.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Implementing the SHA-256 algorithm for DS record support . . . 3		2. Implementing the SHA-256 algorithm for DS record support . . . 3
	2.1. DS record field values . . . . . . . . . . . . . . . . . . 3		2.1. DS record field values . . . . . . . . . . . . . . . . . . 3
	2.2. DS Record with SHA-256 Wire Format . . . . . . . . . . . . 3		2.2. DS Record with SHA-256 Wire Format . . . . . . . . . . . . 3
	2.3. Example DS Record Using SHA-256 . . . . . . . . . . . . . . 4		2.3. Example DS Record Using SHA-256 . . . . . . . . . . . . . . 4
	3. Implementation Requirements . . . . . . . . . . . . . . . . . . 4		3. Implementation Requirements . . . . . . . . . . . . . . . . . . 4
	4. Deployment Considerations . . . . . . . . . . . . . . . . . . . 5		4. Deployment Considerations . . . . . . . . . . . . . . . . . . . 4
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
	6. Security 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		7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6		8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 6		8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
	8.2. Informative References . . . . . . . . . . . . . . . . . . 6		8.2. Informative References . . . . . . . . . . . . . . . . . . 7
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
	Intellectual Property and Copyright Statements . . . . . . . . . . 8		Intellectual Property and Copyright Statements . . . . . . . . . . 9
	1. Introduction		1. Introduction
	The DNSSEC [RFC4033] [RFC4034] [RFC4035] DS RR is published in parent		The DNSSEC [RFC4033] [RFC4034] [RFC4035] DS RR is published in parent
	zones to distribute a cryptographic digest of a child's Key Signing		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		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		parent zone's private zone data signing keys for each algorithm in
	use by the parent. Each signature is published in an RRSIG resource		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		record, owned by the same domain as the DS RRset and with a type
	covered of DS.		covered of DS.
	skipping to change at page 4, line 21		skipping to change at page 4, line 21
	/ Digest (length for SHA-256 is 32 bytes) /		/ Digest (length for SHA-256 is 32 bytes) /
	/ /		/ /
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
	2.3. Example DS Record Using SHA-256		2.3. Example DS Record Using SHA-256
	The following is an example DNSKEY and matching DS record. This		The following is an example DNSKEY and matching DS record. This
	DNSKEY record comes from the example DNSKEY/DS records found in		DNSKEY record comes from the example DNSKEY/DS records found in
	section 5.4 of [RFC4034].		section 5.4 of [RFC4034].
	The DNSKEY record::		The DNSKEY record:
	dskey.example.com. 86400 IN DNSKEY 256 3 5 ( AQOeiiR0GOMYkDshWoSKz9Xz		dskey.example.com. 86400 IN DNSKEY 256 3 5 ( AQOeiiR0GOMYkDshWoSKz9Xz
	fwJr1AYtsmx3TGkJaNXVbfi/		fwJr1AYtsmx3TGkJaNXVbfi/
	2pHm822aJ5iI9BMzNXxeYCmZ		2pHm822aJ5iI9BMzNXxeYCmZ
	DRD99WYwYqUSdjMmmAphXdvx		DRD99WYwYqUSdjMmmAphXdvx
	egXd/M5+X7OrzKBaMbCVdFLU		egXd/M5+X7OrzKBaMbCVdFLU
	Uh6DhweJBjEVv5f2wwjM9Xzc		Uh6DhweJBjEVv5f2wwjM9Xzc
	nOf+EPbtG9DMBmADjFDc2w/r		nOf+EPbtG9DMBmADjFDc2w/r
	ljwvFw==		ljwvFw==
	) ; key id = 60485		) ; key id = 60485
	skipping to change at page 4, line 44		skipping to change at page 4, line 44
	256 digest: [RFC Editor: please replace XXX with the assigned digest		256 digest: [RFC Editor: please replace XXX with the assigned digest
	type (likely 2):]		type (likely 2):]
	dskey.example.com. 86400 IN DS 60485 5 XXX ( D4B7D520E7BB5F0F67674A0C		dskey.example.com. 86400 IN DS 60485 5 XXX ( D4B7D520E7BB5F0F67674A0C
	CEB1E3E0614B93C4F9E99B83		CEB1E3E0614B93C4F9E99B83
	83F6A1E4469DA50A )		83F6A1E4469DA50A )
	3. Implementation Requirements		3. Implementation Requirements
	Implementations MUST support the use of the SHA-256 algorithm in DS		Implementations MUST support the use of the SHA-256 algorithm in DS
	RRs.		RRs. Validator implementations SHOULD ignore DS RRs containing SHA-1
			digests if DS RRs with SHA-256 digests are present in the DS RRset.
	Validator implementations MUST, by default, ignore DS RRs containing
	SHA-1 digests if DS RRs with SHA-256 digests are present in the DS
	RRset. This behavior SHOULD be the default. Validator
	implementations MAY provide configuration settings that allow network
	operators to specify preference policy when validating multiple DS
	records containing different digest types.
	4. Deployment Considerations		4. Deployment Considerations
	If a validator does not support the SHA-256 digest type and no other		If a validator does not support the SHA-256 digest type and no other
	DS RR exists in a zone's DS RRset with a supported digest type, then		DS RR exists in a zone's DS RRset with a supported digest type, then
	the validator has no supported authentication path leading from the		the validator has no supported authentication path leading from the
	parent to the child. The resolver should treat this case as it would		parent to the child. The resolver should treat this case as it would
	the case of an authenticated NSEC RRset proving that no DS RRset		the case of an authenticated NSEC RRset proving that no DS RRset
	exists, as described in [RFC4035], section 5.2.		exists, as described in [RFC4035], section 5.2.
	skipping to change at page 5, line 39		skipping to change at page 5, line 34
	use in DS records are as follows:		use in DS records are as follows:
	VALUE Digest Type Status		VALUE Digest Type Status
	0 Reserved -		0 Reserved -
	1 SHA-1 MANDATORY		1 SHA-1 MANDATORY
	2 SHA-256 MANDATORY		2 SHA-256 MANDATORY
	3-255 Unassigned -		3-255 Unassigned -
	6. Security Considerations		6. Security Considerations
			6.1. Potential Digest Type Downgrade Attacks
			A downgrade attack from a stronger digest type to a weaker one is
			possible if all of the following are true:
			o A zone includes multiple DS records for a given child's DNSKEY,
			each of which use a different digest type.
			o A validator accepts a weaker digest even if a stronger one is
			present but invalid.
			For example, if the following conditions are all true:
			o Both SHA-1 and SHA-256 based digests are published in DS records
			within a parent zone for a given child zone's DNSKEY.
			o The DS record with the SHA-1 digest matches the digest computed
			using the child zone's DNSKEY.
			o The DS record with the SHA-256 digest fails to match the signature
			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		Because of the weaknesses recently discovered within the SHA-1
	algorithm, users of DNSSEC are encouraged to deploy the use of SHA-		algorithm, users of DNSSEC are encouraged to deploy the use of SHA-
	256 as soon as the software implementations in use allow for it.		256 as soon as the software implementations in use allow for it.
	At the time of this publication, the SHA-256 digest algorithm is		At the time of this publication, the SHA-256 digest algorithm is
	considered sufficiently strong for the immediate future. It is also		considered sufficiently strong for the immediate future. It is also
	considered sufficient for use in DNSSEC DS RRs for the immediate		considered sufficient for use in DNSSEC DS RRs for the immediate
	future. However, future published attacks may, of course, weaken the		future. However, future published attacks may weaken the usability
	usability of this algorithm within the DS RRs. It is beyond the		of this algorithm within the DS RRs. It is beyond the scope of this
	scope of this document to speculate extensively on the cryptographic		document to speculate extensively on the cryptographic strength of
	strength of the SHA-256 digest algorithm.		the SHA-256 digest algorithm.
	Likewise, it is also beyond the scope of this document to specify		Likewise, it is also beyond the scope of this document to specify
	whether or for how long SHA-1 based DS records should be		whether or for how long SHA-1 based DS records should be
	simultaneously published alongside SHA-256 based DS records.		simultaneously published alongside SHA-256 based DS records.
	7. Acknowledgments		7. Acknowledgments
	This document is a minor extension to the existing DNSSEC documents		This document is a minor extension to the existing DNSSEC documents
	and those authors are gratefully appreciated for the hard work that		and those authors are gratefully appreciated for the hard work that
	went into the base documents.		went into the base documents.
	The following people contributed to portions of this document in some		The following people contributed to portions of this document in some
	fashion: Mark Andrews, Roy Arends, Olafur Gudmundsson, Olaf M.		fashion: Mark Andrews, Roy Arends, Olafur Gudmundsson, Olaf M.
	Kolkman, Edward Lewis, Scott Rose, Sam Weiler.		Kolkman, Edward Lewis, Scott Rose, Stuart E. Schechter, Sam Weiler.
	8. References		8. References
	8.1. Normative References		8.1. Normative References
	[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.		[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
	Rose, "DNS Security Introduction and Requirements",		Rose, "DNS Security Introduction and Requirements",
	RFC 4033, March 2005.		RFC 4033, March 2005.
	[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.		[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
	skipping to change at page 7, line 5		skipping to change at page 7, line 18
	[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.		[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
	Rose, "Protocol Modifications for the DNS Security		Rose, "Protocol Modifications for the DNS Security
	Extensions", RFC 4035, March 2005.		Extensions", RFC 4035, March 2005.
	[SHA256] National Institute of Standards and Technology, "Secure		[SHA256] National Institute of Standards and Technology, "Secure
	Hash Algorithm. NIST FIPS 180-2", August 2002.		Hash Algorithm. NIST FIPS 180-2", August 2002.
	8.2. Informative References		8.2. Informative References
			[SHA256CODE]
			Motorola Labs, "US Secure Hash Algorithms (SHA)",
			June 2005.
	Author's Address		Author's Address
	Wes Hardaker		Wes Hardaker
	Sparta		Sparta
	P.O. Box 382		P.O. Box 382
	Davis 95617		Davis 95617
	US		US
	Email: hardaker@tislabs.com		Email: hardaker@tislabs.com
	skipping to change at page 8, line 41		skipping to change at page 9, line 41
	This document and the information contained herein are provided on an		This document and the information contained herein are provided on an
	"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS		"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
	OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET		OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
	ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,		ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
	INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE		INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
	INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED		INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
	WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.		WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
	Copyright Statement		Copyright Statement
	Copyright (C) The Internet Society (2005). This document is subject		Copyright (C) The Internet Society (2006). This document is subject
	to the rights, licenses and restrictions contained in BCP 78, and		to the rights, licenses and restrictions contained in BCP 78, and
	except as set forth therein, the authors retain all their rights.		except as set forth therein, the authors retain all their rights.
	Acknowledgment		Acknowledgment
	Funding for the RFC Editor function is currently provided by the		Funding for the RFC Editor function is currently provided by the
	Internet Society.		Internet Society.
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