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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (November 2001) is 8195 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 2535 (ref. 'DNSSEC') (Obsoleted by RFC 4033, RFC 4034, RFC 4035) Summary: 5 errors (**), 0 flaws (~~), 6 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNSEXT Working Group D. Massey 3 INTERNET-DRAFT USC/ISI 4 S. Rose 5 Expires: April 2002 NIST 6 Updates: RFC 2535 November 2001 8 Limiting the Scope of the KEY Resource Record 9 ------------------------------ 10 12 Status of this Document 14 This document is an Internet-Draft and is in full conformance with 15 all provisions of Section 10 of RFC2026. Distribution of this 16 document is unlimited. Comments regarding this document should be 17 sent to the author. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that other 21 groups may also distribute working documents as Internet-Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 Abstract 35 This document limits the KEY resource record to only DNS zone keys. 36 The original KEY resource record used sub-typing to store both DNS 37 zone keys and arbitrary application keys. DNS security keys and 38 application keys differ in almost every respect and should not be 39 combined in a single sub-typed resource record. This document 40 removes application keys from the KEY record by redefining the 41 Protocol Octet field in the KEY RDATA. Three existing application key 42 sub-types are changed to historic, but the format of the KEY record 43 is not changed. This document updates RFC 2535. 45 1. Introduction 47 This document limits the scope the KEY resource record. The KEY 48 resource record, originally defined in [DNSSEC], uses resource record 49 sub-typing to hold any public key associated with "a zone, a user, or 50 a host or other end entity". The KEY resource record is assigned 51 type value of 25 and the Protocol Octet in the KEY RDATA identifies 52 the sub-type. DNSSEC Zone, User and Host keys are stored in the KEY 53 resource record and are identified by a Protocol Octet value of 3. 54 Email, IPSEC, and TLS keys are also stored in the KEY resource record 55 and are identified by Protocol Octet values of 1,2, and 4 56 (respectively). Protocol Octet values 5-254 are available for 57 assignment by IANA and values have been requested (but not assigned) 58 for applications such as SSH. 60 Closer examination and limited experimental deployment has shown that 61 application keys stored in KEY records are problematic. Any use of 62 sub-typing has inherent limitations. A resolver can not specify the 63 desired sub-type in a DNS query and many DNS operations group 64 resource records into sets, based on the DNS name and type. For a 65 example, a resolver can not directly request the DNSSEC key sub-type. 66 Instead, the resolver must request all KEY records associated with a 67 DNS name. DNSSEC signatures apply to the set of all KEY resource 68 records associated with the DNS name, regardless of sub-type. 70 In the case of the KEY record, the inherent sub-type limitations are 71 exacerbated since DNS zone keys and application keys differ in 72 virtually every respect. Combining two very different types of keys 73 into a single sub-typed resource record adds unnecessary complexity 74 and increases the potential for implementation and deployment errors. 75 This document addresses these issues by removing all application keys 76 from the KEY resource record. Note that the scope of this document 77 is strictly limited to the KEY record and this document does not 78 endorse or restrict the storage of application keys in other resource 79 records. 81 2. DNS Zone Key and Application Key Differences 83 In the original specification, all public keys were stored in KEY 84 records, regardless of protocol or type. This proved to be a mistake 85 as DNS security keys (zone, host and user) and application keys 86 differ in the following ways: 88 o They serve different purposes. 90 o They are managed by different administrators. 92 o They are authenticated according to different rules. 94 o Nameservers use different rules when including them in 95 responses. 97 o Resolvers process them in different ways. 99 o Faults/key compromises have different consequences. 101 The purpose of a DNS zone key is to sign resource records associated 102 with a DNS zone but the purpose of an application key is specific to 103 the application. DNSSEC host and user KEY RRs are used to generate 104 SIG(0) transaction signatures. Application keys, such as PGP/email, 105 IPSEC, TLS, and SSH keys, are not a mandatory part of any zone and 106 the purpose and proper use of application keys is outside the scope 107 of DNS. 109 DNSSEC keys are managed by DNS administrators, but application keys 110 are managed by application administrators. The DNS zone administra- 111 tor determines the key lifetime, handles any suspected key comprom- 112 ises, and manages any DNSSEC key changes. Likewise, the application 113 administrator is responsible for the same functions for the applica- 114 tion keys related to the application. For example, a user typically 115 manages her own PGP key and a server manages its own TLS key. 116 Application key management tasks are outside the scope of DNS 117 administration. 119 DNS zone keys are used to authenticate application keys, but applica- 120 tion keys MUST NOT be used to authenticate DNS zone keys. A DNS 121 zone key is either configured as trusted key or authenticated by con- 122 structing a chain of trust in the DNS hierarchy. To participate in 123 the chain of trust, a DNS zone must exchange zone key information 124 with its parent zone [DNSSEC]. Application keys are not configured 125 as trusted keys in the DNS and are never part of any DNS chain of 126 trust. Application key data should not be exchanged with the parent 127 zone. A resolver considers an application key authenticated if it 128 has a valid signature from the local DNS zone keys, but applications 129 may impose additional requirements before the application key is 130 accepted as authentic. 132 It MAY be useful for nameservers to include DNS zone keys in the 133 additional section of a response, but application keys are typically 134 not useful unless they have been specifically requested. For exam- 135 ple, it may be useful to include the isi.edu zone key along with a 136 response that contain the www.isi.edu A record and SIG record. A 137 secure resolver will need the isi.edu zone key in order to check the 138 SIG and authenticate the www.isi.edu A record. It is typical not 139 useful to include the IPSEC, email, and TLS keys along with the A 140 record. Note that by placing application keys in the KEY record, a 141 resolver will need the IPSEC, email, TLS, and other key associated 142 with isi.edu if the resolver intends to authenticate the isi.edu zone 143 key (since signatures only apply to the entire KEY set). 145 DNS zone keys require special handling by resolvers, but application 146 keys should be treated the same as any other type of DNS data. The 147 DNSSEC keys are of no value to end applications, unless the applica- 148 tions plan to do their own DNS authentication. Secure resolvers 149 MUST NOT use application keys as part of the authentication process. 150 Application keys have no unique value to resolvers and are only use- 151 ful to the application requesting the key. Note that if sub-types 152 are used to identify the application key, then either the interface 153 to the resolver must specify the sub-type or the application must be 154 able to accept all KEY records and pick out the desired the sub-type. 156 A fault or compromise of DNS zone key can lead to invalid or forged 157 DNS data, but a fault or compromise of an application key should have 158 no impact on other DNS data. Incorrectly adding or changing a DNS 159 zone key can invalidate all of the DNS data in zone and in all of its 160 subzones. By using a compromised key, an attacker can forge data 161 from the effected zone and any for any of its sub-zones. A fault or 162 compromise of an application key has implications for that applica- 163 tion, but it should not have an impact on the DNS. Note that applica- 164 tion key faults and key compromises can have an impact on the entire 165 DNS if the application key and DNS zone keys are both stored in the 166 KEY record. 168 In summary, DNS zone keys and application keys differ in most every 169 respect. DNS zone keys are an essential part of the DNS infrastruc- 170 ture and require special handling by DNS administrators and DNS 171 resolvers. Application keys are simply another type of data and have 172 no special meaning to DNS administrators or resolvers. These two 173 different types of data do not belong in the same resource record. 175 3. Redefinition of the KEY Resource Record 177 The KEY record is redefined as resource record for storing DNSSEC 178 keys. The KEY RDATA format, as defined in [DNSSEC], is not changed, 179 but the Protocol Octet is redefined as follows: 181 VALUE Protocol 182 0 - reserved 183 1 HISTORIC 184 2 HISTORIC 185 3 dnssec 186 4 HISTORIC 188 5-254 - reserved 189 255 HISTORIC 191 All valid KEY records MUST have a Protocol Octet value of 3. KEY 192 records with a Protocol Octet value other than 3 SHOULD NOT be stored 193 in the DNS and SHOULD be ignored by nameservers and resolvers that 194 receive them in a response. 196 4. Backward Compatibility 198 Protocol Octet values of 1,2, 4, and 255 were previously defined in 199 RFC 2535. These values are now deprecated. To insure backward 200 compatibility, the Protocol Octet values 1,2, and 4 will be desig- 201 nated as HISTORIC. Protocol values 5-254 are reserved and are no 202 longer available for assignment by IANA. 204 KEY records with a Protocol Value of 1,2, or 4 were never widely 205 deployed in the DNS and some limited test deployment revealed prob- 206 lems. Most notably, placing application keys in the KEY record can 207 create very large key sets and application keys that appear in the 208 zone apex can create zone management problems. Some change in the 209 definition and/or usage of the KEY record would be required even if 210 the approach described here were not required. 212 KEY records with a Protocol Octet value of 1,2, or 4 SHOULD NOT be 213 place in a DNS zone. Likewise, resolvers that receive KEY records 214 in a response with HISTORIC or invalid protocol field values SHOULD 215 be ignored and SHOULD NOT be stored in a resolver's/server's cache. 217 No changes are made to the format of the KEY record or to the use of 218 DNSSEC zone, host and user keys. Existing nameservers and resolvers 219 will continue to correctly process KEY records that contain DNSSEC 220 keys. 222 5. Storing Application Keys in the DNS 224 The scope of this document is strictly limited to the KEY record. 225 This document prohibits storing application keys in the KEY record, 226 but it does not endorse or restrict the storing application keys in 227 other record types. Other documents should describe how DNS handles 228 application keys. 230 6. IANA Consideration 232 Protocol Octet values 1,2,4, and 255 are changed to HISTORIC. 234 Protocol Octet values 5-255 are reserved and are no longer available 235 for assignment by IANA. 237 7. Security Consideration 239 This document eliminates potential security problems that could arise 240 due to the coupling of DNS zone keys and application keys. 242 Prior to the change described in the document, a correctly authenti- 243 cated KEY set could include both application keys and DNSSEC keys. 244 If one of the application keys is compromised, it could be used as a 245 false zone key to create phony DNS signatures (SIG records). 246 Resolvers that do not carefully check the KEY sub-type may believe 247 these false signatures and incorrectly authenticate DNS data. With 248 this change, application keys cannot appear in an authenticated KEY 249 set. 251 Applications that accept keys based solely on DNSSEC rely on the DNS 252 administrator to correctly enter the application key data and are 253 only as secure as the weakest zone in the DNS chain of trust. 254 Compromises or errors caused by DNS administrators when entering 255 DNSSEC data could results in an application key failing to verify, or 256 verified incorrectly. 258 The format and correct usage of DNS zone keys is not changed by this 259 document and no new security considerations are introduced. 261 8. Intellectual Property 263 The IETF takes no position regarding the validity or scope of any 264 intellectual property or other rights that might be claimed to per- 265 tain to the implementation or use of the technology described in this 266 document or the extent to which any license under such rights might 267 or might not be available; neither does it represent that it has made 268 any effort to identify any such rights. Information on the IETF's 269 procedures with respect to rights in standards-track and standards- 270 related documentation can be found in BCP-11. 272 Copies of claims of rights made available for publication and any 273 assurances of licenses to be made available, or the result of an 274 attempt made to obtain a general license or permission for the use of 275 such proprietary rights by implementors or users of this specifica- 276 tion can be obtained from the IETF Secretariat. 278 The IETF invites any interested party to bring to its attention any 279 copyrights, patents or patent applications, or other proprietary 280 rights which may cover technology that may be required to practice 281 this standard. Please address the information to the IETF Executive 282 Director. 284 9. References 286 [DNSSEC] Eastlake, D., "Domain Name System Security Extensions", RFC 287 2535, March 1999. 289 10. Author Information 291 Daniel Massey 292 USC Information Sciences Institute 293 3811 North Fairfax Drive, Suite 200 294 Arlington, VA 22203 296 Scott Rose 297 National Institute for Standards and Technology 298 Gaithersburg, MD 300 Expiration and File Name: 302 This draft, titled expires April 2001 304 Full Copyright Statement 306 Copyright (C) The Internet Society (2001). All Rights Reserved. 308 This document and translations of it may be copied and furnished 309 to others, and derivative works that comment on or otherwise explain 310 it or assist in its implementation may be prepared, copied, published 311 and distributed, in whole or in part, without restriction of any 312 kind, provided that the above copy- right notice and this paragraph 313 are included on all such copies and derivative works. However, this 314 document itself may not be modified in any way, such as by removing 315 the copyright notice or references to the Internet Society or other 316 Internet organizations, except as needed for the purpose of developing 317 Internet standards in which case the procedures for copyrights defined 318 in the Internet Standards process must be followed, or as required 319 to translate it into languages other than English. 321 The limited permissions granted above are perpetual and will not 322 be revoked by the Internet Society or its successors or assigns. 324 This document and the information contained herein is provided on 325 an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 326 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 327 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN 328 WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY 329 OR FITNESS FOR A PARTICULAR PURPOSE."