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Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The key words "MAY","MAY NOT", "MUST", "MUST NOT", "REQUIRED", "RECOMMENDED", "SHOULD", and "SHOULD NOT" in this document are to be interpreted as described in RFC2119. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (October 2002) is 7863 days in the past. Is this intentional? 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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNSEXT Working Group Olafur Gudmundsson 3 INTERNET-DRAFT October 2002 4 6 Updates: RFC 1035, RFC 2535, RFC 3008, RFC 3090. 8 Delegation Signer Resource Record 10 Status of this Memo 12 This document is an Internet-Draft and is in full conformance with 13 all provisions of Section 10 of RFC2026. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that 17 other groups may also distribute working documents as Internet- 18 Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six months 21 and may be updated, replaced, or obsoleted by other documents at any 22 time. It is inappropriate to use Internet-Drafts as reference 23 material or to cite them other than as ``work in progress.'' 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/ietf/1id-abstracts.txt 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html 31 Comments should be sent to the authors or the DNSEXT WG mailing list 32 namedroppers@ops.ietf.org 34 This draft expires on April 1, 2003. 36 Copyright Notice 38 Copyright (C) The Internet Society (2002). All rights reserved. 40 Abstract 42 The delegation signer (DS) resource record is inserted at a zone cut 43 (i.e., a delegation point) to indicate that the delegated zone is 44 digitally signed and that the delegated zone recognizes the indicated 45 key as a valid zone key for the delegated zone. The DS RR is a 46 modification to the DNS Security Extensions definition, motivated by 47 operational considerations. The intent is to use this resource record 48 as an explicit statement about the delegation, rather than relying on 49 inference. 51 This document defines the DS RR, gives examples of how it is used and 52 the implications of this record on resolvers. This change is not 53 backwards compatible with RFC 2535. 54 This document updates RFC1035, RFC2535, RFC3008 and RFC3090. 56 1 Introduction 58 Familiarity with the DNS system [RFC1035], DNS security extensions 59 [RFC2535] and DNSSEC terminology [RFC3090] is important. 61 Experience shows that when the same data can reside in two 62 administratively different DNS zones, the data frequently gets out of 63 sync. The presence of an NS RRset in a zone anywhere other than at 64 the apex indicates a zone cut or delegation. The RDATA of the NS 65 RRset specifies the authoritative servers for the delegated or 66 "child" zone. Based on actual measurements, 10-30% of all delegations 67 on the Internet have differing NS RRsets at parent and child. There 68 are a number of reasons for this, including a lack of communication 69 between parent and child and bogus name servers being listed to meet 70 registry requirements. 72 DNSSEC [RFC2535,RFC3008,RFC3090] specifies that a child zone needs to 73 have its KEY RRset signed by its parent to create a verifiable chain 74 of KEYs. There has been some debate on where the signed KEY RRset 75 should reside, whether at the child [RFC2535] or at the parent. If 76 the KEY RRset resides at the child, maintaining the signed KEY RRset 77 in the child requires frequent two-way communication between the two 78 parties. First the child transmits the KEY RRset to the parent and 79 then the parent sends the signature(s) to the child. Storing the KEY 80 RRset at the parent simplifies the communication. 82 DNSSEC [RFC2535] requires that the parent store a NULL KEY record for 83 an unsecure child zone to indicate that the child is unsecure. A NULL 84 KEY record is a waste: an entire signed RRset is used to communicate 85 effectively one bit of information--that the child is unsecure. 86 Chasing down NULL KEY RRsets complicates the resolution process in 87 many cases, because servers for both parent and child need to be 88 queried for the KEY RRset if the child server does not return it. 89 Storing the KEY RRset only in the parent zone simplifies this and 90 would allow the elimination of the NULL KEY RRsets entirely. For 91 large delegation zones the cost of NULL keys is a significant barrier 92 to deployment. 94 Another complication of the DNSSEC key model is that the KEY record 95 can be used to store public keys for other protocols in addition to 96 DNSSEC keys. There are number of potential problems with this, 97 including: 98 1. The KEY RRset can become quite large if many applications and 99 protocols store their keys at the zone apex. Possible protocols 100 are IPSEC, HTTP, SMTP, SSH and others that use public key 101 cryptography. 102 2. The KEY RRset may require frequent updates. 103 3. The probability of compromised or lost keys, which trigger 104 emergency key rollover procedures, increases. 105 4. The parent may refuse sign KEY RRsets with non-DNSSEC zone keys. 106 5. The parent may not meet the child's expectations in turnaround 107 time for resigning the KEY RRset. 109 Given these and other reasons, there is good reason to explore 110 alternatives to using only KEY records to create a chain of trust. 112 Some of these problems can be reduced or eliminated by operational 113 rules or protocol changes. To reduce the number of keys at the zone 114 apex, a rule to require applications to store their KEY records at 115 the SRV name for that application is one possibility. Another is to 116 restrict the KEY record to only DNSSEC keys and create a new record 117 type for all non-DNSSEC keys. A third possible solution is to 118 prohibit the storage of non-DNSSEC keys at the zone apex. There are 119 other possible solutions, but they are outside the scope of this 120 document. 122 1.2 Reserved Words 124 The key words "MAY","MAY NOT", "MUST", "MUST NOT", "REQUIRED", 125 "RECOMMENDED", "SHOULD", and "SHOULD NOT" in this document are to be 126 interpreted as described in RFC2119. 128 2 Specification of the Delegation key Signer 130 This section defines the Delegation Signer (DS) RR type and the 131 changes to DNS to accommodate it. 133 2.1 Delegation Signer Record Model 135 This document presents a replacement for the DNSSEC KEY record chain 136 of trust [RFC2535] that uses a new RR that resides only at the 137 parent. This record identifies the key(s) that the child uses to 138 self-sign its own KEY RRset. 140 The chain of trust is now established by verifying the parent KEY 141 RRset, the DS RRset from the parent and the KEY RRset at the child. 143 This is cryptographically equivalent to using just KEY records. 145 Communication between the parent and child is greatly reduced, since 146 the child only needs to notify the parent about changes in keys that 147 sign its apex KEY RRset. The parent is ignorant of all other keys in 148 the child's apex KEY RRset. Furthermore, the child maintains full 149 control over the apex KEY RRset and its content. The child can 150 maintain any policies regarding its KEY usage for DNSSEC and other 151 applications and protocols with minimal impact on the parent. Thus if 152 the child wants to have frequent key rollover for its DNS zone keys, 153 the parent does not need to be aware of it: the child can use one key 154 to sign only its apex KEY RRset and other keys to sign the other 155 RRsets in the zone. 157 This model fits well with a slow roll out of DNSSEC and the islands 158 of security model. In this model, someone who trusts "good.example." 159 can preconfigure a key from "good.example." as a trusted key, and 160 from then on trusts any data signed by that key or that has a chain 161 of trust to that key. If "example." starts advertising DS records, 162 "good.example." does not have to change operations by suspending 163 self-signing. DS records can also be used to identify trusted keys 164 instead of KEY records. Another significant advantage is that the 165 amount of information stored in large delegation zones is reduced: 166 rather than the NULL KEY record at every unsecure delegation required 167 by RFC 2535, only secure delegations require additional information 168 in the form of a signed DS RRset. 170 The main disadvantage of this approach is that verifying a zone's KEY 171 RRset requires two signature verification operations instead of the 172 one required by RFC 2535. There is no impact on the number of 173 signatures verified for other types of RRsets. 175 2.2 Protocol Change 177 All DNS servers and resolvers that support DS MUST support the OK bit 178 [RFC3225] and a larger message size [RFC3226]. In order for a 179 delegation to be considered secure the delegation MUST contain a DS 180 RRset. If a query contains the OK bit, a server returning a referral 181 for the delegation MUST include the following RRsets in the authority 182 section in this order: 183 If DS RRset is present: 184 parent NS RRset 185 DS and SIG(DS) 186 If no DS RRset is present: 187 parent NS RRset 188 parent NXT and SIG(NXT) 190 This increases the size of referral messages and may cause some or 191 all glue to be omitted. If the DS or NXT RRsets with signatures do 192 not fit in the DNS message, the TC bit MUST be set. Additional 193 section processing is not changed. 195 A DS RRset accompanying an NS RRset indicates that the child zone is 196 secure. If an NS RRset exists without a DS RRset, the child zone is 197 unsecure (from the parents point of view). DS RRsets MUST NOT appear 198 at non-delegation points or at a zone's apex. 200 Section 2.2.1 defines the behavior of the corner case of non 201 recursive server that is only authorative for the child. The 202 following section 2.2.2 replaces RFC2535 sections 2.3.4 and 3.4, 203 section 2.2.3 replaces RFC3008 section 2.7, and RFC3090 updates are 204 in section 2.2.4. 206 2.2.1 Authorative servers special processing 208 A server that is authorative for both parent and child, a DS aware 209 server will return DS from the parent zone. A non DS aware server is 210 expected to answer: 211 RCODE: NOERROR 212 AA bit: set 213 Answer Section: Empty 214 Authority Section: SOA [+ SIG(SOA) + NXT + SIG(NXT)] 215 This indicates there is no DS at the apex. If the server is DS aware 216 and does not perform recursive lookup for the DS, it MUST return the 217 above answer. The reason is to avoid confusing resolvers that are non 218 DS aware. In the early deployment of DS, most resolvers will be non- 219 DS aware thus send DS queries to child servers rather than parent 220 ones. 222 A DS aware recursive server that is authorative for the child, MAY 223 perform a recursive query to search for the DS record, if the RD bit 224 is set. If this server has the DS in cache it MUST return it without 225 the AA bit. 227 2.2.2 RFC2535 2.3.4 and 3.4: Special Considerations at Delegation Points 229 DNS security views each zone as a unit of data completely under the 230 control of the zone owner with each entry (RRset) signed by a special 231 private key held by the zone manager. But the DNS protocol views the 232 leaf nodes in a zone that are also the apex nodes of a child zone 233 (i.e., delegation points) as "really" belonging to the child zone. 234 The corresponding domain names appear in two master files and might 235 have RRsets signed by both the parent and child zones' keys. A 236 retrieval could get a mixture of these RRsets and SIGs, especially 237 since one server could be serving both the zone above and below a 238 delegation point [RFC 2181]. 240 Each DS RRset stored in the parent zone MUST be signed by, at least, 241 one of the parent zone's private key. The parent zone MUST NOT 242 contain a KEY RRset at any delegation point. Delegations in the 243 parent MAY contain only the following RR types: NS, DS, NXT and SIG. 244 The NS RRset MUST NOT be signed. The NXT RRset is the exceptional 245 case: it will always appear differently and authoritatively in both 246 the parent and child zones if both are secure. 248 A secure zone MUST contain a self-signed KEY RRset at its apex. Upon 249 verifying the DS RRset from the parent, a resolver MAY trust any KEY 250 identified in the DS RRset as a valid signer of the child's apex KEY 251 RRset. Resolvers configured to trust one of the keys signing the KEY 252 RRset MAY now treat any data signed by the zone keys in the KEY RRset 253 as secure. In all other cases resolvers MUST consider the zone 254 unsecure. A DS RRset MUST NOT appear at a zone's apex. 256 An authoritative server queried for type DS MUST return the DS RRset 257 in the answer section. 259 2.2.3 Signer's Name (replaces RFC3008 section 2.7) 261 The signer's name field of a SIG RR MUST contain the name of the zone 262 to which the data and signature belong. The combination of signer's 263 name, key tag, and algorithm MUST identify a zone key if the SIG is 264 to be considered material. This document defines a standard policy 265 for DNSSEC validation; local policy may override the standard policy. 267 There are no restrictions on the signer field of a SIG(0) record. 268 The combination of signer's name, key tag, and algorithm MUST 269 identify a key if this SIG(0) is to be processed. 271 2.2.4 Changes to RFC3090 273 A number of sections of RFC3090 need to be updated to reflect the DS 274 record. 276 2.2.4.1 RFC3090: Updates to section 1: Introduction 278 Most of the text is still relevant but the words ``NULL key'' are to 279 be replaced with ``missing DS RRset''. In section 1.3 the last three 280 paragraphs discuss the confusion in sections of RFC 2535 that are 281 replaced in section 2.2.1 above. Therefore, these paragraphs are now 282 obsolete. 284 2.2.4.2 RFC3090 section 2.1: Globally Secured 286 Rule 2.1.b is replaced by the following rule: 288 2.1.b. The KEY RRset at a zone's apex MUST be self-signed by a 289 private key whose public counterpart MUST appear in a zone signing 290 KEY RR (2.a) owned by the zone's apex and specifying a mandatory-to- 291 implement algorithm. This KEY RR MUST be identified by a DS RR in a 292 signed DS RRset in the parent zone. 294 If a zone cannot get its parent to advertise a DS record for it, the 295 child zone cannot be considered globally secured. The only exception 296 to this is the root zone, for which there is no parent zone. 298 2.2.4.3 RFC3090 section 3: Experimental Status. 300 The only difference between experimental status and globally secured 301 is the missing DS RRset in the parent zone. All locally secured zones 302 are experimental. 304 2.3 Comments on Protocol Changes 306 Over the years there have been various discussions surrounding the 307 DNS delegation model, declaring it to be broken because there is no 308 good way to assert if a delegation exists. In the RFC2535 version of 309 DNSSEC, the presence of the NS bit in the NXT bit map proves there is 310 a delegation at this name. Something more explicit is needed and the 311 DS record addresses this need for secure delegations. 313 The DS record is a major change to DNS: it is the first resource 314 record that can appear only on the upper side of a delegation. Adding 315 it will cause interoperabilty problems and requires a flag day for 316 DNSSEC. Many old servers and resolvers MUST be upgraded to take 317 advantage of DS. Some old servers will be able to be authoritative 318 for zones with DS records but will not add the NXT or DS records to 319 the authority section. The same is true for caching servers; in 320 fact, some may even refuse to pass on the DS or NXT records. 322 2.4 Wire Format of the DS record 324 The DS (type=TDB) record contains these fields: key tag, algorithm, 325 digest type, and the digest of a public key KEY record that is 326 allowed and/or used to sign the child's apex KEY RRset. Other keys 327 MAY sign the child's apex KEY RRset. 329 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 330 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 1 331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 332 | key tag | algorithm | Digest type | 333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 334 | SHA-1 digest | 335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 336 | (20 bytes) | 337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 338 | | 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 340 | | 341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 342 | | 343 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 345 The key tag is calculated as specified in RFC2535. Algorithm MUST be 346 an algorithm number assigned in the range 1..251 and the algorithm 347 MUST be allowed to sign DNS data. The digest type is an identifier 348 for the digest algorithm used. The digest is calculated over the 349 canonical name of the delegated domain name followed by the whole 350 RDATA of the KEY record (all four fields). 352 digest = hash( canonical FQDN on KEY RR | KEY_RR_rdata) 354 KEY_RR_rdata = Flags | Protocol | Algorithm | Public Key 356 Digest type value 0 is reserved, value 1 is SHA-1, and reserving 357 other types requires IETF standards action. For interoperabilty 358 reasons, as few digest algorithms as possible should be reserved. The 359 only reason to reserve additional digest types is to increase 360 security. 362 DS records MUST point to zone KEY records that are allowed to 363 authenticate DNS data. The indicated KEY record's protocol field 364 MUST be set to 3; flag field bits 0 and 6 MUST be set to 0; bit 7 365 MUST be set to 1. The value of other bits is not significant for the 366 purposes of this document. 368 The size of the DS RDATA for type 1 (SHA-1) is 24 bytes, regardless 369 of key size, new digest types probably will have larger digests. 371 2.4.1 Justifications for Fields 373 The algorithm and key tag fields are present to allow resolvers to 374 quickly identify the candidate KEY records to examine. SHA-1 is a 375 strong cryptographic checksum: it is computationally infeasible for 376 an attacker to generate a KEY record that has the same SHA-1 digest. 377 Combining the name of the key and the key rdata as input to the 378 digest provides stronger assurance of the binding. Having the key 379 tag in the DS record adds greater assurance than the SHA-1 digest 380 alone, as there are now two different mapping functions that a KEY RR 381 must match. 383 This format allows concise representation of the keys that the child 384 will use, thus keeping down the size of the answer for the 385 delegation, reducing the probability of DNS message overflow. The 386 SHA-1 hash is strong enough to uniquely identify the key and is 387 similar to the PGP key footprint. The digest type field is present 388 for possible future expansion. 390 The DS record is well suited to listing trusted keys for islands of 391 security in configuration files. 393 2.5 Presentation Format of the DS Record 395 The presentation format of the DS record consists of three numbers 396 (key tag, algorithm and digest type) followed by the digest itself 397 presented in hex: 398 example. DS 12345 3 1 123456789abcdef67890123456789abcdef67890 400 2.6 Transition Issues for Installed Base 402 No backwards compatibility with RFC2535 is provided. 404 RFC2535-compliant resolvers will assume that all DS-secured 405 delegations are locally secure. This is bad, but the DNSEXT Working 406 Group has determined that rather than dealing with both 407 RFC2535-secured zones and DS-secured zones, a rapid adoption of DS is 408 preferable. Thus the only option for early adopters is to upgrade to 409 DS as soon as possible. 411 2.6.1 Backwards compatibility with RFC2535 and RFC1035 413 This section documents how a resolver determines the type of 414 delegation. 415 RFC1035 delegation (in parent) has: 417 RFC1035 NS 419 RFC2535 adds the following two cases: 421 Secure RFC2535: NS + NXT + SIG(NXT) 422 NXT bit map contains: NS SIG NXT 423 Unsecure RFC2535: NS + KEY + SIG(KEY) + NXT + SIG(NXT) 424 NXT bit map contains: NS SIG KEY NXT 425 KEY must be a NULL key. 427 DNSSEC with DS has the following two states: 429 Secure DS: NS + DS + SIG(DS) 430 NXT bit map contains: NS SIG NXT DS 431 Unsecure DS: NS + NXT + SIG(NXT) 432 NXT bit map contains: NS SIG NXT 434 It is difficult for a resolver to determine if a delegation is secure 435 RFC 2535 or unsecure DS. This could be overcome by adding a flag to 436 the NXT bit map, but only upgraded resolvers would understand this 437 flag, anyway. Having both parent and child signatures for a KEY RRset 438 might allow old resolvers to accept a zone as secure, but the cost of 439 doing this for a long time is much higher than just prohibiting RFC 440 2535-style signatures at child zone apexes and forcing rapid 441 deployment of DS-enabled servers and resolvers. 443 RFC 2535 and DS can in theory be deployed in parallel, but this would 444 require resolvers to deal with RFC 2535 configurations forever. This 445 document obsoletes the NULL KEY in parent zones, which is a difficult 446 enough change that a flag day is required. 448 2.7 KEY and corresponding DS record example 450 This is a example of a KEY record and corresponding DS record. 452 dskey.example. KEY 256 3 1 ( 453 AQPwHb4UL1U9RHaU8qP+Ts5bVOU1s7fYbj2b3CCbzNdj 454 4+/ECd18yKiyUQqKqQFWW5T3iVc8SJOKnueJHt/Jb/wt 455 ) ; key id = 28668 456 DS 28668 1 1 49FD46E6C4B45C55D4AC69CBD3CD34AC1AFE51DE 458 3 Resolver 460 3.1 DS Example 462 To create a chain of trust, a resolver goes from trusted KEY to DS to 463 KEY. 465 Assume the key for domain "example." is trusted. Zone "example." 466 contains at least the following records: 467 example. SOA 468 example. NS ns.example. 469 example. KEY 470 example. NXT NS SOA KEY SIG NXT secure.example. 471 example. SIG(SOA) 472 example. SIG(NS) 473 example. SIG(NXT) 474 example. SIG(KEY) 475 secure.example. NS ns1.secure.example. 476 secure.example. DS tag=12345 alg=3 digest_type=1 477 secure.example. NXT NS SIG NXT DS unsecure.example. 478 secure.example. SIG(NXT) 479 secure.example. SIG(DS) 480 unsecure.example NS ns1.unsecure.example. 481 unsecure.example. NXT NS SIG NXT example. 482 unsecure.example. SIG(NXT) 484 In zone "secure.example." following records exist: 485 secure.example. SOA 486 secure.example. NS ns1.secure.example. 487 secure.example. KEY 488 secure.example. KEY 489 secure.example. NXT 490 secure.example. SIG(KEY) 491 secure.example. SIG(SOA) 492 secure.example. SIG(NS) 493 secure.example. SIG(NXT) 495 In this example the private key for "example." signs the DS record 496 for "secure.example.", making that a secure delegation. The DS record 497 states which key is expected to sign the KEY RRset at 498 "secure.example.". Here "secure.example." signs its KEY RRset with 499 the KEY identified in the DS RRset, thus the KEY RRset is validated 500 and trusted. 502 This example has only one DS record for the child, but parents MUST 503 allow multiple DS records to facilitate key rollover and multiple KEY 504 algorithms. 506 The resolver determines the security status of "unsecure.example." by 507 examining the parent zone's NXT record for this name. The absence of 508 the DS bit indicates an unsecure delegation. Note the NXT record 509 SHOULD only be examined after verifying the corresponding signature. 511 3.1 Resolver Cost Estimates for DS Records 513 From a RFC2535 resolver point of view, for each delegation followed 514 to chase down an answer, one KEY RRset has to be verified. 515 Additional RRsets might also need to be verified based on local 516 policy (e.g., the contents of the NS RRset). Once the resolver gets 517 to the appropriate delegation, validating the answer might require 518 verifying one or more signatures. A simple A record lookup requires 519 at least N delegations to be verified and one RRset. For a DS-enabled 520 resolver, the cost is 2N+1. For an MX record, where the target of 521 the MX record is in the same zone as the MX record, the costs are N+2 522 and 2N+2, for RFC 2535 and DS, respectively. In the case of negatives 523 answer the same ratios hold true. 525 The resolver may require an extra query to get the DS record and this 526 may add to the overall cost of the query, but this is never worse 527 than chasing down NULL KEY records from the parent in RFC2535 DNSSEC. 529 DS adds processing overhead on resolvers and increases the size of 530 delegation answers, but much less than storing signatures in the 531 parent zone. 533 4 Security Considerations: 535 This document proposes a change to the validation chain of KEY 536 records in DNSSEC. The change is not believed to reduce security in 537 the overall system. In RFC2535 DNSSEC, the child zone has to 538 communicate keys to its parent and prudent parents will require some 539 authentication with that transaction. The modified protocol will 540 require the same authentication, but allows the child to exert more 541 local control over its own KEY RRset. 543 There is a remote possibility that an attacker could generate a valid 544 KEY that matches all the DS fields, of a specific DS set, and thus 545 forge data from the child. This possibility is considered 546 impractical, as on average more than 547 2 ^ (160 - ) 548 keys would have to be generated before a match would be found. 550 An attacker that wants to match any DS record will have to generate 551 on average at least 2^80 keys. 553 The DS record represents a change to the DNSSEC protocol and there is 554 an installed base of implementations, as well as textbooks on how to 555 set up secure delegations. Implementations that do not understand the 556 DS record will not be able to follow the KEY to DS to KEY chain and 557 will consider all zones secured that way as unsecure. 559 5 IANA Considerations: 561 IANA needs to allocate an RR type code for DS from the standard RR 562 type space (type 43 requested). 564 IANA needs to open a new registry for the DS RR type for digest 565 algorithms. Defined types are: 566 0 is Reserved, 567 1 is SHA-1. 568 Adding new reservations requires IETF standards action. 570 6 Acknowledgments 572 Over the last few years a number of people have contributed ideas 573 that are captured in this document. The core idea of using one key to 574 sign only the KEY RRset comes from discussions with Bill Manning and 575 Perry Metzger on how to put in a single root key in all resolvers. 576 Alexis Yushin, Brian Wellington, Paul Vixie, Jakob Schlyter, Scott 577 Rose, Edward Lewis, Lars-Johan Liman, Matt Larson, Mark Kosters, Dan 578 Massey, Olaf Kolman, Phillip Hallam-Baker, Miek Gieben, Havard 579 Eidnes, Donald Eastlake 3rd., Randy Bush, David Blacka, Steve 580 Bellovin, Rob Austein, Derek Atkins, Roy Arends, Harald Alvestrand, 581 and others have provided useful comments. 583 Normative References: 585 [RFC1035] P. Mockapetris, ``Domain Names - Implementation and 586 Specification'', STD 13, RFC 1035, November 1987. 588 [RFC2181] R. Elz, R. Bush, ``Clarifications to the DNS Specification'', 589 RFC 2181, July 1997. 591 [RFC2535] D. Eastlake, ``Domain Name System Security Extensions'', RFC 592 2535, March 1999. 594 [RFC3008] B. Wellington, ``Domain Name System Security (DNSSEC) Signing 595 Authority'', RFC 3008, November 2000. 597 [RFC3090] E. Lewis `` DNS Security Extension Clarification on Zone 598 Status'', RFC 3090, March 2001. 600 [RFC3225] D. Conrad, ``Indicating Resolver Support of DNSSEC'', RFC 601 3225, December 2001. 603 [RFC3226] O. Gudmundsson, ``DNSSEC and IPv6 A6 aware server/resolver 604 message size requirements'', RFC 3226, December 2001. 606 Author Address 608 Olafur Gudmundsson 609 3826 Legation Street, NW 610 Washington, DC, 20015 611 USA 612 614 Full Copyright Statement 616 Copyright (C) The Internet Society (2002). All Rights Reserved. 618 This document and translations of it may be copied and furnished to 619 others, and derivative works that comment on or otherwise explain it 620 or assist in its implementation may be prepared, copied, published 621 and distributed, in whole or in part, without restriction of any 622 kind, provided that the above copyright notice and this paragraph are 623 included on all such copies and derivative works. However, this 624 document itself may not be modified in any way, such as by removing 625 the copyright notice or references to the Internet Society or other 626 Internet organizations, except as needed for the purpose of 627 developing Internet standards in which case the procedures for 628 copyrights defined in the Internet Standards process must be 629 followed, or as required to translate it into languages other than 630 English. 632 The limited permissions granted above are perpetual and will not be 633 revoked by the Internet Society or its successors or assigns. 635 This document and the information contained herein is provided on an 636 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 637 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 638 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 639 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 640 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."