DNSEXT Working GroupD. Massey INTERNET-DRAFTUSC/ISI S. Rose Expires: April 2002NIST Updates: RFC 2535 November 2001Limiting the Scope of the KEY Resource Record ------------------------------ <draft-ietf-dnsext-restrict-key-for-dnssec-00.txt>draft-ietf-dnsext-restrict-key-for-dnssec-01.txt Status of this Document This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Distribution of this document is unlimited. Comments regarding this document should be sent to the author. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months 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. Abstract This document limits the KEY resource record to only DNS zoneDNSSEC keys. The original KEY resource record used sub-typing to store both DNS zoneDNSSEC keys and arbitrary application keys. DNS security keysStoring both DNSSEC and application keys differ in almost every respect and should not be combinedin one record was a single sub-typed resource record.mistake. This document removes application keys from the KEY record by redefining the Protocol Octet field in the KEY RDATA. 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 historic, but the format of the KEY record is not changed. This document updates RFC 2535. 1.1 Introduction This document limits the scope the KEY resource record. The KEY resource record, originallyrecord was defined in [DNSSEC], uses[DNSSEC] and used resource record sub-typing to hold anyarbitrary public key associated with "a zone, a user, or a host or other end entity". Thekeys 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 resourcerecord (hence sub-typing is assigned type valueessentially eliminated) and all but one of 25the KEY record flags are also eliminated. Section 2 presents the motivation for restricting the KEY record and Section ?? defines the Protocol Octet inrevised KEY record. Section 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 flabs, does not change DNSSEC keys. 2 Motivation for Restricting the KEY Record The KEY record RDATA [DNSSEC] consists of flags, a Protocol Octet, an Algorithm type, and a public key. The Protocol Octet identifies the KEY record sub-type. DNSSEC Zone, User and Hostpublic keys are stored in the KEY resource record and are identified byusing a Protocol Octet value of 3. Email, IPSEC, and TLS keys are also stored in the KEY resource record and are identified byusing Protocol Octet values of 1,2, and 4 (respectively). Protocol Octet values 5-254 are available for assignment by IANA and values have been requested (but not assigned) for applications such as SSH. Closer examination and limited experimental deployment has shown that application keys stored in KEY records are problematic.Any use of sub-typing has inherent limitations. A resolver can not specify the desired sub-type in a DNS query and manymost DNS operations groupapply only to resource records into sets, based on the DNS name and type.sets. For a example, a resolver can not directly request the DNSSEC keyKEY records with a particular sub-type. Instead, the resolver must request all KEY records associated with a DNS name.name and then search the set for the desired 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 DNS zonethe sub-type is used to distinguish between DNSSEC keys and application keys. DNSSEC keys and application keys differ in virtually every respect.respect and Section 2.1 discusses these differences in more detail. Combining twothese very different types of keys into a single sub-typed resource record adds unnecessary complexity and increases the potential for implementation and deployment errors. This document addresses these issuesLimited 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. DNS Zone Key2.1 Differences Between DNSSEC and Application Key Differences In the original specification, all publicKeys DNSSEC keys were stored in KEY records, regardlessare an essential part of the DNSSEC protocol or type. This provedand are used by both name servers and resolvers in order to be a mistake asperform DNS securitytasks. A DNS zone, used to sign and authenticate RR sets, is most common example of a DNSSEC key. SIG(0) and TKEY also use DNSSEC keys. Application keys (zone, hostsuch as Email keys, IPSEC keys, and user)TLS keys and applicationare simply another type data. These keys differ in the following ways:have no special meaning to a name server or resolver. o They serve different purposes. o They are managed by different administrators. o They are authenticated according to different rules. o Nameservers use different rules when including them in responses. o Resolvers process them in different ways. o Faults/key compromises have different consequences. The purpose of a DNS zoneDNSSEC key is to sign resource records associated with a DNS zone but(or generate DNS transaction signatures in the case of SIG(0)/TKEY). But the purpose of an application key is specific to the application. DNSSEC host and user KEY RRs are used to generate SIG(0) transaction signatures.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. DNSSEC keys are managed by DNS administrators, but application keys are managed by application administrators. The DNS zone administra- toradministrator determines the key lifetime, handles any suspected key comprom- ises,compromises, and manages any DNSSEC key changes. Likewise, the application administrator is responsible for the same functions for the applica- tionapplication 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. DNSDNSSEC zone keys are used to authenticate application keys, but applica- tionapplication keys MUST NOT be used to authenticate DNS zone keys. A DNS zone key is either configured as trusted key or authenticated by con- structingconstructing a chain of trust in the DNS hierarchy. To participate in the chain of trust, a DNS zone must exchange zone key information with its parent zone [DNSSEC]. 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 may impose additional requirements before the application key is accepted as authentic. 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 exam- ple,example, it may 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 set). DNS zone keys require special handling by resolvers, but application keys should be treated the same as any other type of DNS data. The DNSSEC keys are of no value to end applications, unless the applica- tionsapplications 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 use- fuluseful 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 must specify the sub-type or the application must be able to accept all KEY records and pick out the desired the sub-type. A fault or compromise of 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 applica- tion,application, but it should not have an impact on the DNS. Note that applica- tionapplication 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, DNS zoneDNSSEC keys and application keys differ in most every respect. DNS zoneDNSSEC keys are an essential part of the DNS infrastruc- tureinfrastructure 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. Redefinition3 Definition of the KEY Resource Record The KEY record uses type 25 and is redefinedused as resource record for storing DNSSEC keys. The KEYRDATA format, as defined in [DNSSEC], is not changed, butfor a KEY RR consists of flags, a protocol octet, the Protocol Octetalgorithm number octet, and the public key itself. The format is redefinedas follows: VALUE Protocol1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 - reserved1 HISTORIC2 HISTORIC3 dnssec4 HISTORIC 5-254 -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 / / / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| In the flags field, all bits except bit 7 are reserved 255 HISTORIC All validshould be zero. If Bit 7 (Zone bit) is set to 1, then the KEY records MUST haveis a Protocol Octet value of 3.DNS Zone key. If Bit 7 is set to 0, the KEY records withis not a Protocol Octet value other than 3 SHOULD NOTzone key. SIG(0)/TKEY are examples of DNSSEC keys that are not zone keys. The protocol field must be stored inset 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 DNSzone key flag are eliminated: o The A/C bits (bits 0 and SHOULD1) are eliminated and must be ignored by nameservers0. o The extended flags bit (bit 3) is eliminated and resolvers that receive them in a response. 4. Backward Compatibility Protocol Octet values of 1,2, 4,must be 0. o The host/user bit (bit 6) is eliminated and 255 were previously defined in RFC 2535. These valuesmust be 0. o The zone bit (bit 7) remains unchanged. o The signatory field (bits 12-15) are now deprecated. To insure backward compatibility, the Protocol Octet values 1,2,eliminated by [SDU] and 4 willmust be desig- nated as HISTORIC.0. o Bits 2,4,5,8,9,10,11 remain unchanged. They are reserved and must be zero. All Protocol Octet values 5-254except DNSSEC (3) are reservedeliminated: o Value 1 (Email) is renamed to reserved. o Value 2 (IPSEC) is renamed to reserved. o Value 3 (DNSSEC) is unchanged. o Value 4 (TLS) is renamed to reserved. o Value 5-254 remains unchanged (reserved). o Value 255 (ANY) is renamed to reserved. Name servers and are no longer available for assignment by IANA.resolvers SHOULD reject any KEY recordswith a Protocol Value of 1,2, or 4 were never widely deployed in the DNSother than 3. The algorithm and some limited test deployment revealed prob- lems. Most notably, placingpublic key fields are not changed. 5 Backward Compatibility No backwards compatibility is provided for application keys. Any Email, IPSEC, or TLS keys in the KEY record can create very large key setsare now deprecated and applicationSHOULD be rejected by name servers and resolvers. However, problems with applications keys that appear in(such as keys at the zoneapex can create zone management problems. Someand large RR sets) and have already been identified some change in the definition and/or usage of the KEY record would be required even if the approach described here were not required. DNSSEC zone KEY records with a Protocol Octet value of 1,2, or 4 SHOULD NOT be place in a DNS zone. Likewise, resolvers that receive KEY records in a response with HISTORIC or invalid protocol field values SHOULD be ignored and SHOULD NOT be stored in a resolver's/server's cache. No changesare made tonot change and remain backwards compatible. A properly formatted RFC 2535 zone KEY would have all flag bits, other than the format ofZone Bit (Bit 7), set to 0 and would have the KEY record orProtocol Octet set to 3. This remains true under the use ofrestricted KEY. DNSSEC zone,non-zone KEY records (SIG(0)/TKEY keys) are backwards compatible, but the distinction between host and user keys. Existingkeys (flag bit 6) is lost. Overall, existing nameservers and resolvers will continue to correctly process KEY records that containwith a sub-type of DNSSEC keys. 5.6 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 should describe how DNS handles application keys. 6.7 IANA Consideration KEY record Protocol Octet values 1,2,4, and 255 areshould be changed to HISTORIC.reserved. Assignment of any future KEY record Protocol Octet values 5-255 are reserved and are no longer available for assignment by IANA. 7.requires a standards action. 8 Security Consideration 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 the document, a correctly authenti- catedauthenticated 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 phony DNS signatures (SIG records). Resolvers that do not carefully check the KEY sub-type may believe these false signatures and incorrectly authenticate DNS data. With this change, application keys cannot appear in an authenticated KEY set. Applications that accept keys based solely on DNSSEC rely on the DNS administrator to correctly enter the application key dataset and are only as secure as the weakest zone in the DNS chain of trust. Compromises or errors caused by DNS administrators when entering DNSSEC data could results in an application key failing to verify, or verified incorrectly.this vulnerability is eliminated. The format and correct usage of DNS zoneDNSSEC keys is not changed by this document and no new security considerations are introduced. 8.9 Intellectual Property The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to per- tainpertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards- related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specifica- tionspecification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 9.10 References [DNSSEC] Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999. 10.[SDU] Wellington, B., "Secure Domain Name System (DNS) Dynamic Update", RFC 3007, November 2000. 11 Author Information Daniel Massey <firstname.lastname@example.org> USC Information Sciences Institute 3811 North Fairfax Drive, Suite 200 Arlington, VA 22203 Scott Rose <email@example.com> National Institute for Standards and Technology Gaithersburg, MD Expiration and File Name: This draft, titled <draft-ietf-dnsext-restrict-key-for-dnssec-00.txt> expires April 2001Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. 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