draft-ietf-dnsext-ds-sha256-05.txt		rfc4509.txt
	Network Working Group W. Hardaker		Network Working Group W. Hardaker
	Internet-Draft Sparta		Request for Comments: 4509 Sparta
	Expires: August 25, 2006 February 21, 2006		Category: Standards Track May 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-sha256-05.txt
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	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2006).		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 DNSKEYs in a child zone.
	child zone.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction ....................................................2
	2. Implementing the SHA-256 algorithm for DS record support . . . 3		2. Implementing the SHA-256 Algorithm for DS Record Support ........2
	2.1. DS record field values . . . . . . . . . . . . . . . . . . 3		2.1. DS Record Field Values .....................................2
	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 ............................3
	3. Implementation Requirements . . . . . . . . . . . . . . . . . . 4		3. Implementation Requirements .....................................3
	4. Deployment Considerations . . . . . . . . . . . . . . . . . . . 4		4. Deployment Considerations .......................................4
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5		5. IANA Considerations .............................................4
	6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5		6. Security Considerations .........................................4
	6.1. Potential Digest Type Downgrade Attacks . . . . . . . . . . 5		6.1. Potential Digest Type Downgrade Attacks ....................4
	6.2. SHA-1 vs SHA-256 Considerations for DS Records . . . . . . 6		6.2. SHA-1 vs SHA-256 Considerations for DS Records .............5
	7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6		7. Acknowledgements ................................................5
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7		8. References ......................................................6
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 7		8.1. Normative References .......................................6
	8.2. Informative References . . . . . . . . . . . . . . . . . . 7		8.2. Informative References .....................................6
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 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 one key in a child's
	Key (KSK) DNSKEY RR. The DS RRset is signed by at least one of the		DNSKEY RRset. The DS RRset is signed by at least one of the parent
	parent zone's private zone data signing keys for each algorithm in		zone's private zone data signing keys for each algorithm in use by
	use by the parent. Each signature is published in an RRSIG resource		the parent. Each signature is published in an RRSIG resource record,
	record, owned by the same domain as the DS RRset and with a type		owned by the same domain as the DS RRset, with a type covered of DS.
	covered of DS.
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		In this document, the key words "MUST", "MUST NOT", "REQUIRED",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
	document are to be interpreted as described in [RFC2119].		and "OPTIONAL" are to be interpreted as described in [RFC2119].
	2. Implementing the SHA-256 algorithm for DS record support		2. Implementing the SHA-256 Algorithm for DS Record Support
	This document specifies that the digest type code [XXX: To be		This document specifies that the digest type code 2 has been assigned
	assigned by IANA; likely 2] is to be assigned to SHA-256 [SHA256]		to SHA-256 [SHA256] [SHA256CODE] for use within DS records. The
	[SHA256CODE] for use within DS records. The results of the digest		results of the digest algorithm MUST NOT be truncated, and the entire
	algorithm MUST NOT be truncated and the entire 32 byte digest result		32 byte digest result is to be published in the DS record.
	is to be published in the DS record.
	2.1. DS record field values		2.1. DS Record Field Values
	Using the SHA-256 digest algorithm within a DS record will make use		Using the SHA-256 digest algorithm within a DS record will make use
	of the following DS-record fields:		of the following DS-record fields:
	Digest type: [XXX: To be assigned by IANA; likely 2]		Digest type: 2
	Digest: A SHA-256 bit digest value calculated by using the following		Digest: A SHA-256 bit digest value calculated by using the following
	formula ("|" denotes concatenation). The resulting value is not		formula ("|" denotes concatenation). The resulting value is not
	truncated and the entire 32 byte result is to used in the		truncated, and the entire 32 byte result is to be used in the
	resulting DS record and related calculations.		resulting DS record and related calculations.
	digest = SHA_256(DNSKEY owner name | DNSKEY RDATA)		digest = SHA_256(DNSKEY owner name | DNSKEY RDATA)
	where DNSKEY RDATA is defined by [RFC4034] as:		where DNSKEY RDATA is defined by [RFC4034] as:
	DNSKEY RDATA = Flags | Protocol | Algorithm | Public Key		DNSKEY RDATA = Flags | Protocol | Algorithm | Public Key
	The Key Tag field and Algorithm fields remain unchanged by this		The Key Tag field and Algorithm fields remain unchanged by this
	document and are specified in the [RFC4034] specification.		document and are specified in the [RFC4034] specification.
	2.2. DS Record with SHA-256 Wire Format		2.2. DS Record with SHA-256 Wire Format
	The resulting on-the-wire format for the resulting DS record will be		The resulting on-the-wire format for the resulting DS record will be
	[XXX: IANA assignment should replace the 2 below]:		as follows:
	1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3		1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Key Tag | Algorithm | DigestType=2 |		| Key Tag | Algorithm | DigestType=2 |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	/ /		/ /
	/ Digest (length for SHA-256 is 32 bytes) /		/ Digest (length for SHA-256 is 32 bytes) /
	/ /		/ /
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
	skipping to change at page 4, line 33		skipping to change at page 3, line 38
	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
	The resulting DS record covering the above DNSKEY record using a SHA-		The resulting DS record covering the above DNSKEY record using a
	256 digest: [RFC Editor: please replace XXX with the assigned digest		SHA-256 digest:
	type (likely 2):]
	dskey.example.com. 86400 IN DS 60485 5 XXX ( D4B7D520E7BB5F0F67674A0C		dskey.example.com. 86400 IN DS 60485 5 2 ( 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. Validator implementations SHOULD ignore DS RRs containing SHA-1		RRs. Validator implementations SHOULD ignore DS RRs containing SHA-1
	digests if DS RRs with SHA-256 digests are present in the DS RRset.		digests if DS RRs with SHA-256 digests are present in the DS RRset.
	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.
	Because zone administrators can not control the deployment speed of		Because zone administrators can not control the deployment speed of
	support for SHA-256 in validators that may be referencing any of		support for SHA-256 in validators that may be referencing any of
	their zones, zone operators should consider deploying both SHA-1 and		their zones, zone operators should consider deploying both SHA-1 and
	SHA-256 based DS records. This should be done for every DNSKEY for		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		which DS records are being generated. Whether to make use of both
	digest types and for how long is a policy decision that extends		digest types and for how long is a policy decision that extends
	beyond the scope of this document.		beyond the scope of this document.
	5. IANA Considerations		5. IANA Considerations
	Only one IANA action is required by this document:		Only one IANA action is required by this document:
	The Digest Type to be used for supporting SHA-256 within DS records		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		has been assigned by IANA.
	Type value of 2 be assigned to the SHA-256 digest algorithm.
	At the time of this writing, the current digest types assigned for		At the time of this writing, the current digest types assigned for
	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		6.1. Potential Digest Type Downgrade Attacks
	A downgrade attack from a stronger digest type to a weaker one is		A downgrade attack from a stronger digest type to a weaker one is
	possible if all of the following are true:		possible if all of the following are true:
	o A zone includes multiple DS records for a given child's DNSKEY,		o A zone includes multiple DS records for a given child's DNSKEY,
	each of which use a different digest type.		each of which uses a different digest type.
	o A validator accepts a weaker digest even if a stronger one is		o A validator accepts a weaker digest even if a stronger one is
	present but invalid.		present but invalid.
	For example, if the following conditions are all true:		For example, if the following conditions are all true:
	o Both SHA-1 and SHA-256 based digests are published in DS records		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.		within a parent zone for a given child zone's DNSKEY.
	o The DS record with the SHA-1 digest matches the digest computed		o The DS record with the SHA-1 digest matches the digest computed
	using the child zone's DNSKEY.		using the child zone's DNSKEY.
	o The DS record with the SHA-256 digest fails to match the digest		o The DS record with the SHA-256 digest fails to match the digest
	computed using the child zone's DNSKEY.		computed using the child zone's DNSKEY.
	Then if the validator accepts the above situation as secure then this		Then, if the validator accepts the above situation as secure, then
	can be used as a downgrade attack since the stronger SHA-256 digest		this can be used as a downgrade attack since the stronger SHA-256
	is ignored.		digest is ignored.
	6.2. SHA-1 vs SHA-256 Considerations for DS Records		6.2. SHA-1 vs. SHA-256 Considerations for DS Records
	Users of DNSSEC are encouraged to deploy SHA-256 as soon as software		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		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		resilient to attack than SHA-1, and confidence in SHA-1's strength is
	being eroded by recently-announced attacks. Regardless of whether or		being eroded by recently announced attacks. Regardless of whether
	not the attacks on SHA-1 will affect DNSSEC, it is believed (at the		the attacks on SHA-1 will affect DNSSEC, it is believed (at the time
	time of this writing) that SHA-256 is the better choice for use in DS		of this writing) that SHA-256 is the better choice for use in DS
	records.		records.
	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 weaken the usability		future. However, future published attacks may weaken the usability
	of this algorithm within the DS RRs. It is beyond the scope of this		of this algorithm within the DS RRs. It is beyond the scope of this
	document to speculate extensively on the cryptographic strength of		document to speculate extensively on the cryptographic 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. Acknowledgements
	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, Paul Hoffman,		fashion: Mark Andrews, Roy Arends, Olafur Gudmundsson, Paul Hoffman,
	Olaf M. Kolkman, Edward Lewis, Scott Rose, Stuart E. Schechter, Sam		Olaf M. Kolkman, Edward Lewis, Scott Rose, Stuart E. Schechter, Sam
	Weiler.		Weiler.
	8. References		8. References
	8.1. Normative References		8.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[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
	RFC 4033, March 2005.		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.
	Rose, "Resource Records for the DNS Security Extensions",		Rose, "Resource Records for the DNS Security
	RFC 4034, March 2005.		Extensions", RFC 4034, March 2005.
	[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]		[SHA256CODE] Eastlake, D., "US Secure Hash Algorithms (SHA)", Work in
	Eastlake, D., "US Secure Hash Algorithms (SHA)",		Progress.
	June 2005.
	Author's Address		Author's Address
	Wes Hardaker		Wes Hardaker
	Sparta		Sparta
	P.O. Box 382		P.O. Box 382
	Davis, CA 95617		Davis, CA 95617
	US		USA
	Email: hardaker@tislabs.com		EMail: hardaker@tislabs.com
	Intellectual Property Statement		Full Copyright Statement
			Copyright (C) The Internet Society (2006).
			This document is subject to the rights, licenses and restrictions
			contained in BCP 78, and except as set forth therein, the authors
			retain all their rights.
			This document and the information contained herein are provided on an
			"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
			OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
			ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
			INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
			INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
			WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
			Intellectual Property
	The IETF takes no position regarding the validity or scope of any		The IETF takes no position regarding the validity or scope of any
	Intellectual Property Rights or other rights that might be claimed to		Intellectual Property Rights or other rights that might be claimed to
	pertain to the implementation or use of the technology described in		pertain to the implementation or use of the technology described in
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	skipping to change at page 9, line 29		skipping to change at page 7, line 45
	such proprietary rights by implementers or users of this		such proprietary rights by implementers or users of this
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	http://www.ietf.org/ipr.		http://www.ietf.org/ipr.
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	Disclaimer of Validity		Acknowledgement
	This document and the information contained herein are provided on an
	"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
	OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
	ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
	INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
	INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
	WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
	Copyright Statement
	Copyright (C) The Internet Society (2006). This document is subject
	to the rights, licenses and restrictions contained in BCP 78, and
	except as set forth therein, the authors retain all their rights.
	Acknowledgment
	Funding for the RFC Editor function is currently provided by the		Funding for the RFC Editor function is provided by the IETF
	Internet Society.		Administrative Support Activity (IASA).
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