< draft-ietf-dnsext-restrict-key-for-dnssec-03.txt		draft-ietf-dnsext-restrict-key-for-dnssec-04.txt >
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	DNS Extensions D. Massey		RFC 3445
	Internet-Draft USC/ISI
	Expires: December 27, 2002 S. Rose
	NIST
	June 28, 2002
	Limiting the Scope of the KEY Resource Record
	draft-ietf-dnsext-restrict-key-for-dnssec-03
	Status of this Memo
	This document is an Internet-Draft and is in full conformance with
	all provisions of Section 10 of RFC2026.
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	This Internet-Draft will expire on December 27, 2002.
	Copyright Notice
	Copyright (C) The Internet Society (2002). All Rights Reserved.
	Abstract
	This document limits the Domain Name System KEY resource record to
	only keys used by the Domain Name System Security Extensions
	(DNSSEC). The original KEY resource record used sub-typing to store
	both DNSSEC keys and arbitrary application keys. Storing both DNSSEC
	and application keys in one record was a mistake. This document
	removes application keys from the KEY record by redefining the
	Protocol Octet field in the KEY Resource Record Data. As a result of
	removing application keys, all but one of the flags in the KEY record
	become unnecessary and are removed. Three existing application key
	sub-types are changed to reserved, but the format of the KEY record
	is not changed. This document updates RFC 2535.
	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.
	Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Motivation for Restricting the KEY Record . . . . . . . . . . 4
	2.1 Differences Between DNSSEC and Application Keys . . . . . . . 4
	3. Definition of the KEY Resource Record . . . . . . . . . . . . 7
	4. Changes from RFC 2535 KEY Record . . . . . . . . . . . . . . . 8
	5. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 10
	6. Storing Application Keys in the DNS . . . . . . . . . . . . . 11
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
	References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14
	Full Copyright Statement . . . . . . . . . . . . . . . . . . . 15
	1. Introduction
	This document limits the scope the KEY resource record. The KEY
	resource record was defined in [2] and used resource record sub-
	typing to hold arbitrary public keys such as Email, IPSEC, DNSSEC,
	and TLS keys. This document eliminates the existing Email, IPSEC,
	and TLS sub-types and prohibits the introduction of new sub-types.
	DNSSEC will be the only allowable sub-type for the KEY record (hence
	sub-typing is essentially eliminated) and all but one of the KEY
	record flags are also eliminated.
	Section 2 presents the motivation for restricting the KEY record and
	Section 3 defines the revised KEY record. Sections 4 and 5 summarize
	the changes from RFC 2535 and discuss backwards compatibility. It is
	important to note that this document restricts the use of the KEY
	record and simplifies the flags, but does not change the definition
	or use of DNSSEC keys.
	2. Motivation for Restricting the KEY Record
	The KEY record RDATA [2] consists of Flags, a Protocol Octet, an
	Algorithm type, and a Public Key. The Protocol Octet identifies the
	KEY record sub-type. DNSSEC public keys are stored in the KEY record
	using a Protocol Octet value of 3. Email, IPSEC, and TLS keys were
	also stored in the KEY record and used Protocol Octet values of 1,2,
	and 4 (respectively). Protocol Octet values 5-254 were available for
	assignment by IANA and values were requested (but not assigned) for
	applications such as SSH.
	Any use of sub-typing has inherent limitations. A resolver can not
	specify the desired sub-type in a DNS query and most DNS operations
	apply only to resource records sets. For example, a resolver can not
	directly request the DNSSEC subtype KEY records. Instead, the
	resolver has to request all KEY records associated with a DNS name
	and then search the set for the desired DNSSEC sub-type. DNSSEC
	signatures also apply to the set of all KEY resource records
	associated with the DNS name, regardless of sub-type.
	In the case of the KEY record, the inherent sub-type limitations are
	exacerbated since the sub-type is used to distinguish between DNSSEC
	keys and application keys. DNSSEC keys and application keys differ
	in virtually every respect and Section 2.1 discusses these
	differences in more detail. Combining these very different types of
	keys into a single sub-typed resource record adds unnecessary
	complexity and increases the potential for implementation and
	deployment errors. Limited experimental deployment has shown that
	application keys stored in KEY records are problematic.
	This document addresses these issues by removing all application keys
	from the KEY resource record. Note that the scope of this document
	is strictly limited to the KEY record and this document does not
	endorse or restrict the storage of application keys in other resource
	records.
	2.1 Differences Between DNSSEC and Application Keys
	DNSSEC keys are an essential part of the DNSSEC protocol and are used
	by both name servers and resolvers in order to perform DNS tasks. A
	DNS zone key, used to sign and authenticate RR sets, is the most
	common example of a DNSSEC key. SIG(0) [3] and TKEY [2] also use
	DNSSEC keys.
	Application keys such as Email keys, IPSEC keys, and TLS keys are
	simply another type data. These keys have no special meaning to a
	name server or resolver.
	The following table summarizes some of the differences between DNSSEC
	keys and Application keys:
	1. They serve different purposes.
	2. They are managed by different administrators.
	3. They are authenticated according to different rules.
	4. Nameservers use different rules when including them in responses.
	5. Resolvers process them in different ways.
	6. Faults/key compromises have different consequences.
	1. The purpose of a DNSSEC key is to sign resource records
	associated with a DNS zone (or generate DNS transaction signatures
	in the case of SIG(0)/TKEY). But the purpose of an application key
	is specific to the application. Application keys, such as PGP/email,
	IPSEC, TLS, and SSH keys, are not a mandatory part of any zone and
	the purpose and proper use of application keys is outside the scope
	of DNS.
	2. DNSSEC keys are managed by DNS administrators, but application
	keys are managed by application administrators. The DNS zone
	administrator determines the key lifetime, handles any suspected key
	compromises, and manages any DNSSEC key changes. Likewise, the
	application administrator is responsible for the same functions for
	the application keys related to the application. For example, a user
	typically manages her own PGP key and a server manages its own TLS
	key. Application key management tasks are outside the scope of DNS
	administration.
	3. DNSSEC zone keys are used to authenticate application keys, but
	application keys MUST NOT be used to authenticate DNS zone keys. A
	DNS zone key is either configured as trusted key or authenticated by
	constructing a chain of trust in the DNS hierarchy. To participate
	in the chain of trust, a DNS zone needs to exchange zone key
	information with its parent zone [2]. Application keys are not
	configured as trusted keys in the DNS and are never part of any DNS
	chain of trust. Application key data SHOULD not be exchanged with
	the parent zone. A resolver considers an application key
	authenticated if it has a valid signature from the local DNS zone
	keys, but applications could impose additional requirements before
	the application key is accepted as authentic.
	4. It MAY be useful for nameservers to include DNS zone keys in the
	additional section of a response, but application keys are typically
	not useful unless they have been specifically requested. For
	example, it could be useful to include the isi.edu zone key along
	with a response that contain the www.isi.edu A record and SIG record.
	A secure resolver will need the isi.edu zone key in order to check
	the SIG and authenticate the www.isi.edu A record. It is typical not
	useful to include the IPSEC, email, and TLS keys along with the A
	record. Note that by placing application keys in the KEY record, a
	resolver will need the IPSEC, email, TLS, and other key associated
	with isi.edu if the resolver intends to authenticate the isi.edu zone
	key (since signatures only apply to the entire KEY RR set).
	5. DNS zone keys require special handling by resolvers, but
	application keys are treated the same as any other type of DNS data.
	The DNSSEC keys are of no value to end applications, unless the
	applications plan to do their own DNS authentication. Secure
	resolvers MUST NOT use application keys as part of the authentication
	process. Application keys have no unique value to resolvers and are
	only useful to the application requesting the key. Note that if sub-
	types are used to identify the application key, then either the
	interface to the resolver needs to specify the sub-type or the
	application needs to be able to accept all KEY records and pick out
	the desired the sub-type.
	6. A fault or compromise of a DNS zone key can lead to invalid or
	forged DNS data, but a fault or compromise of an application key
	SHOULD have no impact on other DNS data. Incorrectly adding or
	changing a DNS zone key can invalidate all of the DNS data in zone
	and in all of its subzones. By using a compromised key, an attacker
	can forge data from the effected zone and any for any of its sub-
	zones. A fault or compromise of an application key has implications
	for that application, but it SHOULD not have an impact on the DNS.
	Note that application key faults and key compromises can have an
	impact on the entire DNS if the application key and DNS zone keys are
	both stored in the KEY record.
	In summary, DNSSEC keys and application keys differ in most every
	respect. DNSSEC keys are an essential part of the DNS infrastructure
	and require special handling by DNS administrators and DNS resolvers.
	Application keys are simply another type of data and have no special
	meaning to DNS administrators or resolvers. These two different
	types of data do not belong in the same resource record.
	3. Definition of the KEY Resource Record
	The KEY record uses type 25 and is used as resource record for
	storing DNSSEC keys. The RDATA for a KEY RR consists of flags, a
	protocol octet, the algorithm number octet, and the public key
	itself. The format is as follows:
	---------------------------------------------------------------------
	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
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| flags | protocol | algorithm |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| /
	/ public key /
	/ /
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	KEY RR Format
	---------------------------------------------------------------------
	In the flags field, all bits except bit 7 are reserved and SHOULD be
	zero. If Bit 7 (Zone bit) is set to 1, then the KEY is a DNS Zone
	key. If Bit 7 is set to 0, the KEY is not a zone key. SIG(0)/TKEY
	are examples of DNSSEC keys that are not zone keys.
	The protocol field MUST be set to 3.
	The algorithm and public key fields are not changed.
	4. Changes from RFC 2535 KEY Record
	The KEY RDATA format is not changed.
	All flags except for the zone key flag are eliminated:
	The A/C bits (bits 0 and 1) are eliminated. They MUST be set to 0
	and MUST be ignored by the receiver.
	The extended flags bit (bit 3) is eliminated. It MUST be set to 0
	and MUST be ignored by the receiver.
	The host/user bit (bit 6) is eliminated. It MUST be set to 0 and
	MUST be ignored by the receiver.
	The zone bit (bit 7) remains unchanged.
	The signatory field (bits 12-15) are eliminated by [4]. They MUST
	be set to 0 and MUST be ignored by the receiver.
	Bits 2,4,5,8,9,10,11 remain unchanged. They are reserved, MUST be
	set to zero and MUST be ignored by the receiver.
	Assignment of any future KEY record Flag values requires a standards
	action.
	All Protocol Octet values except DNSSEC (3) are eliminated:
	Value 1 (Email) is renamed to reserved.
	Value 2 (IPSEC) is renamed to reserved.
	Value 3 (DNSSEC) is unchanged.
	Value 4 (TLS) is renamed to reserved.
	Value 5-254 remains unchanged (reserved).
	Value 255 (ANY) is renamed to reserved.
	The authoritative data for a zone MUST NOT include any KEY records
	with a protocol octet other than 3. Any future KEY record Protocol
	Octet values requires a standards action.
	Name servers and resolvers SHOULD accept KEY RR sets that contain KEY
	records with a value other than 3. If out of date DNS zones contain
	deprecated KEY records with a protocol octet value other than 3, then
	simply dropping the deprecated KEY records from the KEY RR set would
	invalidate any associated SIG record(s) and could create caching
	consistency problems. Note that KEY records with a protocol octet
	value other than 3 MUST NOT be used to authenticate DNS data.
	The algorithm and public key fields are not changed.
	5. Backward Compatibility
	DNSSEC zone key records are not changed and remain backwards
	compatible. A properly formatted RFC 2535 zone KEY would have all
	flag bits, other than the Zone Bit (Bit 7), set to 0 and would have
	the Protocol Octet set to 3. This remains true under the restricted
	KEY.
	DNSSEC non-zone key records (SIG(0)/TKEY keys) are backwards
	compatible, but the distinction between host and user keys (flag bit
	6) is lost.
	No backwards compatibility is provided for application keys. Any
	Email, IPSEC, or TLS keys are now deprecated. Storing application
	keys in the KEY record created problems such as keys at the apex and
	large RR sets and some change in the definition and/or usage of the
	KEY record would have been required even if the approach described
	here were not adopted.
	Overall, existing nameservers and resolvers will continue to
	correctly process KEY records with a sub-type of DNSSEC keys.
	6. Storing Application Keys in the DNS
	The scope of this document is strictly limited to the KEY record.
	This document prohibits storing application keys in the KEY record,
	but it does not endorse or restrict the storing application keys in
	other record types. Other documents can describe how DNS handles
	application keys.
	7. IANA Considerations
	RFC 2535 created an IANA registry for DNS KEY Resource Record
	Protocol Octet values. Values to 1,2,3, 4, and 255 were assigned by
	RFC 2535 and values 5-254 were made available for assignment by IANA.
	This document makes two sets of changes to this registry.
	First, this document re-assigns DNS KEY Resource Record Protocol
	Octet values 1, 2, 4, and 255 to ``reserved''. DNS Key Resource
	Record Protocol Octet Value 3 remains unchanged as ``DNSSEC''.
	Second, new values are no longer available for assignment by IANA and
	this document closes the IANA registry for DNS KEY Resource Record
	Protocol Octet Values. Assignment of any future KEY Resource Record
	Protocol Octet values requires a standards action.
	8. Security Considerations
	This document eliminates potential security problems that could arise
	due to the coupling of DNS zone keys and application keys. Prior to
	the change described in this document, a correctly authenticated KEY
	set could include both application keys and DNSSEC keys. If one of
	the application keys is compromised, it could be used as a false zone
	key to create false DNS signatures (SIG records). Resolvers that do
	not carefully check the KEY sub-type could believe these false
	signatures and incorrectly authenticate DNS data. With this change,
	application keys cannot appear in an authenticated KEY set and this
	vulnerability is eliminated.
	The format and correct usage of DNSSEC keys is not changed by this
	document and no new security considerations are introduced.
	References (Normative)
	[1] Eastlake, D., "Domain Name System Security Extensions", RFC
	2535, March 1999.
	[2] Eastlake, D., "Secret Key Establishment for DNS (TKEY RR)", RFC
	2930, September 2000.
	[3] Eastlake, D., "DNS Request and Transaction Signatures (
	SIG(0)s)", RFC 2931, September 2000.
	[4] Wellington, B., "Secure Domain Name System (DNS) Dynamic
	Update", RFC 3007, November 2000.
	Authors' Addresses		Title: Limiting the Scope of the KEY Resource Record (RR)
			Author(s): D. Massey, S. Rose
			Status: Standards Track
			Date: December 2002
			Mailbox: masseyd@isi.edu, scott.rose@nist.gov
			Pages: 10
			Characters: 20947
			Updates: 2535
	Dan Massey		I-D Tag: draft-ietf-dnsext-restrict-key-for-dnssec-04.txt
	USC Information Sciences Institute
	3811 N. Fairfax Drive
	Arlington, VA 22203
	USA
	EMail: masseyd@isi.edu		URL: ftp://ftp.rfc-editor.org/in-notes/rfc3445.txt
	Scott Rose		This document limits the Domain Name System (DNS) KEY Resource Record
	National Institute for Standards and Technology		(RR) to only keys used by the Domain Name System Security Extensions
	100 Bureau Drive		(DNSSEC). The original KEY RR used sub-typing to store both DNSSEC
	Gaithersburg, MD 20899-3460		keys and arbitrary application keys. Storing both DNSSEC and
	USA		application keys with the same record type is a mistake. This
			document removes application keys from the KEY record by redefining
			the Protocol Octet field in the KEY RR Data. As a result of removing
			application keys, all but one of the flags in the KEY record become
			unnecessary and are redefined. Three existing application key
			sub-types are changed to reserved, but the format of the KEY record is
			not changed. This document updates RFC 2535.
	EMail: scott.rose@nist.gov		This document is a product of the DNS Extensions Working Group of the
			IETF.
	Full Copyright Statement		This is now a Proposed Standard Protocol.
	Copyright (C) The Internet Society (2002). All Rights Reserved.		This document specifies an Internet standards track protocol for
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