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(28 more instances...) -- The abstract seems to indicate that this document updates RFC3090, but the header doesn't have an 'Updates:' line to match this. -- The abstract seems to indicate that this document updates RFC1035, but the header doesn't have an 'Updates:' line to match this. -- The abstract seems to indicate that this document updates RFC2535, but the header doesn't have an 'Updates:' line to match this. -- The abstract seems to indicate that this document updates RFC3008, but the header doesn't have an 'Updates:' line to match this. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the RFC 3978 Section 5.4 Copyright Line does not match the current year == The "Author's Address" (or "Authors' Addresses") section title is misspelled. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. 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. == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: A server authoritative for only the child zone at a delegation point that is also a caching server MAY (if the RD bit is set in the query) perform recursion to find the DS record at the delegation point, and may return the DS record from its cache. In this case, the AA bit MUST not be set in the response. -- 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 7864 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) -- Missing reference section? 'RFC1035' on line 591 looks like a reference -- Missing reference section? 'RFC2535' on line 597 looks like a reference -- Missing reference section? 'RFC3090' on line 603 looks like a reference -- Missing reference section? 'RFC3008' on line 600 looks like a reference -- Missing reference section? 'RFC3225' on line 606 looks like a reference -- Missing reference section? 'RFC3226' on line 609 looks like a reference -- Missing reference section? 'RFC 2181' on line 216 looks like a reference -- Missing reference section? 'RFC2181' on line 594 looks like a reference Summary: 3 errors (**), 0 flaws (~~), 7 warnings (==), 14 comments (--). 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 16, 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 special considerations related to authoritative 201 servers responding to DS queries. Section 2.2.2 replaces RFC2535 202 sections 2.3.4 and 3.4, section 2.2.3 replaces RFC3008 section 2.7, 203 and section 2.2.4 updates RFC3090. 205 2.2.2 RFC2535 2.3.4 and 3.4: Special Considerations at Delegation Points 207 DNS security views each zone as a unit of data completely under the 208 control of the zone owner with each entry (RRset) signed by a special 209 private key held by the zone manager. But the DNS protocol views the 210 leaf nodes in a zone that are also the apex nodes of a child zone 211 (i.e., delegation points) as "really" belonging to the child zone. 212 The corresponding domain names appear in two master files and might 213 have RRsets signed by both the parent and child zones' keys. A 214 retrieval could get a mixture of these RRsets and SIGs, especially 215 since one server could be serving both the zone above and below a 216 delegation point [RFC 2181]. 218 Each DS RRset stored in the parent zone MUST be signed by, at least, 219 one of the parent zone's private key. The parent zone MUST NOT 220 contain a KEY RRset at any delegation point. Delegations in the 221 parent MAY contain only the following RR types: NS, DS, NXT and SIG. 222 The NS RRset MUST NOT be signed. The NXT RRset is the exceptional 223 case: it will always appear differently and authoritatively in both 224 the parent and child zones if both are secure. 226 A secure zone MUST contain a self-signed KEY RRset at its apex. Upon 227 verifying the DS RRset from the parent, a resolver MAY trust any KEY 228 identified in the DS RRset as a valid signer of the child's apex KEY 229 RRset. Resolvers configured to trust one of the keys signing the KEY 230 RRset MAY now treat any data signed by the zone keys in the KEY RRset 231 as secure. In all other cases resolvers MUST consider the zone 232 unsecure. A DS RRset MUST NOT appear at a zone's apex. 234 An authoritative server queried for type DS MUST return the DS RRset 235 in the answer section. 237 2.2.2.1 Special processing for DS queries 239 When a server is authoritative for the parent zone at a delegation 240 point and receives a query for the DS record at that name, it will 241 return the DS from the parent zone. This is true whether or not it 242 is also authoritative for the child zone. 244 When the server is authoritative for the child zone at a delegation 245 point but not the parent zone, there is no natural response, since 246 the child zone is not authoritative for the DS record at the zone's 247 apex. As these queries are only expected to originate from recursive 248 servers which are not DS-aware, the authoritative server MUST answer 249 with: 250 RCODE: NOERROR 251 AA bit: set 252 Answer Section: Empty 253 Authority Section: SOA [+ SIG(SOA) + NXT + SIG(NXT)] 255 That is, it answers as if it is authoritative and the DS record does 256 not exist. DS-aware recursive servers will query the parent zone at 257 delegation points, so will not be affected by this. 259 A server authoritative for only the child zone at a delegation point 260 that is also a caching server MAY (if the RD bit is set in the query) 261 perform recursion to find the DS record at the delegation point, and 262 may return the DS record from its cache. In this case, the AA bit 263 MUST not be set in the response. 265 2.2.3 Signer's Name (replaces RFC3008 section 2.7) 267 The signer's name field of a SIG RR MUST contain the name of the zone 268 to which the data and signature belong. The combination of signer's 269 name, key tag, and algorithm MUST identify a zone key if the SIG is 270 to be considered material. This document defines a standard policy 271 for DNSSEC validation; local policy may override the standard policy. 273 There are no restrictions on the signer field of a SIG(0) record. 274 The combination of signer's name, key tag, and algorithm MUST 275 identify a key if this SIG(0) is to be processed. 277 2.2.4 Changes to RFC3090 279 A number of sections of RFC3090 need to be updated to reflect the DS 280 record. 282 2.2.4.1 RFC3090: Updates to section 1: Introduction 284 Most of the text is still relevant but the words ``NULL key'' are to 285 be replaced with ``missing DS RRset''. In section 1.3 the last three 286 paragraphs discuss the confusion in sections of RFC 2535 that are 287 replaced in section 2.2.1 above. Therefore, these paragraphs are now 288 obsolete. 290 2.2.4.2 RFC3090 section 2.1: Globally Secured 292 Rule 2.1.b is replaced by the following rule: 294 2.1.b. The KEY RRset at a zone's apex MUST be self-signed by a 295 private key whose public counterpart MUST appear in a zone signing 296 KEY RR (2.a) owned by the zone's apex and specifying a mandatory-to- 297 implement algorithm. This KEY RR MUST be identified by a DS RR in a 298 signed DS RRset in the parent zone. 300 If a zone cannot get its parent to advertise a DS record for it, the 301 child zone cannot be considered globally secured. The only exception 302 to this is the root zone, for which there is no parent zone. 304 2.2.4.3 RFC3090 section 3: Experimental Status. 306 The only difference between experimental status and globally secured 307 is the missing DS RRset in the parent zone. All locally secured zones 308 are experimental. 310 2.3 Comments on Protocol Changes 312 Over the years there have been various discussions surrounding the 313 DNS delegation model, declaring it to be broken because there is no 314 good way to assert if a delegation exists. In the RFC2535 version of 315 DNSSEC, the presence of the NS bit in the NXT bit map proves there is 316 a delegation at this name. Something more explicit is needed and the 317 DS record addresses this need for secure delegations. 319 The DS record is a major change to DNS: it is the first resource 320 record that can appear only on the upper side of a delegation. Adding 321 it will cause interoperabilty problems and requires a flag day for 322 DNSSEC. Many old servers and resolvers MUST be upgraded to take 323 advantage of DS. Some old servers will be able to be authoritative 324 for zones with DS records but will not add the NXT or DS records to 325 the authority section. The same is true for caching servers; in 326 fact, some may even refuse to pass on the DS or NXT records. 328 2.4 Wire Format of the DS record 330 The DS (type=TDB) record contains these fields: key tag, algorithm, 331 digest type, and the digest of a public key KEY record that is 332 allowed and/or used to sign the child's apex KEY RRset. Other keys 333 MAY sign the child's apex KEY RRset. 335 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 336 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 1 337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 338 | key tag | algorithm | Digest type | 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 340 | SHA-1 digest | 341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 342 | (20 bytes) | 343 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 344 | | 345 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 346 | | 347 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 348 | | 349 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 351 The key tag is calculated as specified in RFC2535. Algorithm MUST be 352 an algorithm number assigned in the range 1..251 and the algorithm 353 MUST be allowed to sign DNS data. The digest type is an identifier 354 for the digest algorithm used. The digest is calculated over the 355 canonical name of the delegated domain name followed by the whole 356 RDATA of the KEY record (all four fields). 358 digest = hash( canonical FQDN on KEY RR | KEY_RR_rdata) 360 KEY_RR_rdata = Flags | Protocol | Algorithm | Public Key 362 Digest type value 0 is reserved, value 1 is SHA-1, and reserving 363 other types requires IETF standards action. For interoperabilty 364 reasons, as few digest algorithms as possible should be reserved. The 365 only reason to reserve additional digest types is to increase 366 security. 368 DS records MUST point to zone KEY records that are allowed to 369 authenticate DNS data. The indicated KEY record's protocol field 370 MUST be set to 3; flag field bits 0 and 6 MUST be set to 0; bit 7 371 MUST be set to 1. The value of other bits is not significant for the 372 purposes of this document. 374 The size of the DS RDATA for type 1 (SHA-1) is 24 bytes, regardless 375 of key size, new digest types probably will have larger digests. 377 2.4.1 Justifications for Fields 379 The algorithm and key tag fields are present to allow resolvers to 380 quickly identify the candidate KEY records to examine. SHA-1 is a 381 strong cryptographic checksum: it is computationally infeasible for 382 an attacker to generate a KEY record that has the same SHA-1 digest. 383 Combining the name of the key and the key rdata as input to the 384 digest provides stronger assurance of the binding. Having the key 385 tag in the DS record adds greater assurance than the SHA-1 digest 386 alone, as there are now two different mapping functions that a KEY RR 387 must match. 389 This format allows concise representation of the keys that the child 390 will use, thus keeping down the size of the answer for the 391 delegation, reducing the probability of DNS message overflow. The 392 SHA-1 hash is strong enough to uniquely identify the key and is 393 similar to the PGP key footprint. The digest type field is present 394 for possible future expansion. 396 The DS record is well suited to listing trusted keys for islands of 397 security in configuration files. 399 2.5 Presentation Format of the DS Record 401 The presentation format of the DS record consists of three numbers 402 (key tag, algorithm and digest type) followed by the digest itself 403 presented in hex: 404 example. DS 12345 3 1 123456789abcdef67890123456789abcdef67890 406 2.6 Transition Issues for Installed Base 408 No backwards compatibility with RFC2535 is provided. 410 RFC2535-compliant resolvers will assume that all DS-secured 411 delegations are locally secure. This is bad, but the DNSEXT Working 412 Group has determined that rather than dealing with both 413 RFC2535-secured zones and DS-secured zones, a rapid adoption of DS is 414 preferable. Thus the only option for early adopters is to upgrade to 415 DS as soon as possible. 417 2.6.1 Backwards compatibility with RFC2535 and RFC1035 419 This section documents how a resolver determines the type of 420 delegation. 421 RFC1035 delegation (in parent) has: 423 RFC1035 NS 425 RFC2535 adds the following two cases: 427 Secure RFC2535: NS + NXT + SIG(NXT) 428 NXT bit map contains: NS SIG NXT 429 Unsecure RFC2535: NS + KEY + SIG(KEY) + NXT + SIG(NXT) 430 NXT bit map contains: NS SIG KEY NXT 431 KEY must be a NULL key. 433 DNSSEC with DS has the following two states: 435 Secure DS: NS + DS + SIG(DS) 436 NXT bit map contains: NS SIG NXT DS 437 Unsecure DS: NS + NXT + SIG(NXT) 438 NXT bit map contains: NS SIG NXT 440 It is difficult for a resolver to determine if a delegation is secure 441 RFC 2535 or unsecure DS. This could be overcome by adding a flag to 442 the NXT bit map, but only upgraded resolvers would understand this 443 flag, anyway. Having both parent and child signatures for a KEY RRset 444 might allow old resolvers to accept a zone as secure, but the cost of 445 doing this for a long time is much higher than just prohibiting RFC 446 2535-style signatures at child zone apexes and forcing rapid 447 deployment of DS-enabled servers and resolvers. 449 RFC 2535 and DS can in theory be deployed in parallel, but this would 450 require resolvers to deal with RFC 2535 configurations forever. This 451 document obsoletes the NULL KEY in parent zones, which is a difficult 452 enough change that a flag day is required. 454 2.7 KEY and corresponding DS record example 456 This is a example of a KEY record and corresponding DS record. 458 dskey.example. KEY 256 3 1 ( 459 AQPwHb4UL1U9RHaU8qP+Ts5bVOU1s7fYbj2b3CCbzNdj 460 4+/ECd18yKiyUQqKqQFWW5T3iVc8SJOKnueJHt/Jb/wt 461 ) ; key id = 28668 462 DS 28668 1 1 49FD46E6C4B45C55D4AC69CBD3CD34AC1AFE51DE 464 3 Resolver 466 3.1 DS Example 468 To create a chain of trust, a resolver goes from trusted KEY to DS to 469 KEY. 471 Assume the key for domain "example." is trusted. Zone "example." 472 contains at least the following records: 473 example. SOA 474 example. NS ns.example. 475 example. KEY 476 example. NXT NS SOA KEY SIG NXT secure.example. 477 example. SIG(SOA) 478 example. SIG(NS) 479 example. SIG(NXT) 480 example. SIG(KEY) 481 secure.example. NS ns1.secure.example. 482 secure.example. DS tag=12345 alg=3 digest_type=1 483 secure.example. NXT NS SIG NXT DS unsecure.example. 484 secure.example. SIG(NXT) 485 secure.example. SIG(DS) 486 unsecure.example NS ns1.unsecure.example. 487 unsecure.example. NXT NS SIG NXT example. 488 unsecure.example. SIG(NXT) 490 In zone "secure.example." following records exist: 491 secure.example. SOA 492 secure.example. NS ns1.secure.example. 493 secure.example. KEY 494 secure.example. KEY 495 secure.example. NXT 496 secure.example. SIG(KEY) 497 secure.example. SIG(SOA) 498 secure.example. SIG(NS) 499 secure.example. SIG(NXT) 501 In this example the private key for "example." signs the DS record 502 for "secure.example.", making that a secure delegation. The DS record 503 states which key is expected to sign the KEY RRset at 504 "secure.example.". Here "secure.example." signs its KEY RRset with 505 the KEY identified in the DS RRset, thus the KEY RRset is validated 506 and trusted. 508 This example has only one DS record for the child, but parents MUST 509 allow multiple DS records to facilitate key rollover and multiple KEY 510 algorithms. 512 The resolver determines the security status of "unsecure.example." by 513 examining the parent zone's NXT record for this name. The absence of 514 the DS bit indicates an unsecure delegation. Note the NXT record 515 SHOULD only be examined after verifying the corresponding signature. 517 3.1 Resolver Cost Estimates for DS Records 519 From a RFC2535 resolver point of view, for each delegation followed 520 to chase down an answer, one KEY RRset has to be verified. 521 Additional RRsets might also need to be verified based on local 522 policy (e.g., the contents of the NS RRset). Once the resolver gets 523 to the appropriate delegation, validating the answer might require 524 verifying one or more signatures. A simple A record lookup requires 525 at least N delegations to be verified and one RRset. For a DS-enabled 526 resolver, the cost is 2N+1. For an MX record, where the target of 527 the MX record is in the same zone as the MX record, the costs are N+2 528 and 2N+2, for RFC 2535 and DS, respectively. In the case of negatives 529 answer the same ratios hold true. 531 The resolver may require an extra query to get the DS record and this 532 may add to the overall cost of the query, but this is never worse 533 than chasing down NULL KEY records from the parent in RFC2535 DNSSEC. 535 DS adds processing overhead on resolvers and increases the size of 536 delegation answers, but much less than storing signatures in the 537 parent zone. 539 4 Security Considerations: 541 This document proposes a change to the validation chain of KEY 542 records in DNSSEC. The change is not believed to reduce security in 543 the overall system. In RFC2535 DNSSEC, the child zone has to 544 communicate keys to its parent and prudent parents will require some 545 authentication with that transaction. The modified protocol will 546 require the same authentication, but allows the child to exert more 547 local control over its own KEY RRset. 549 There is a remote possibility that an attacker could generate a valid 550 KEY that matches all the DS fields, of a specific DS set, and thus 551 forge data from the child. This possibility is considered 552 impractical, as on average more than 553 2 ^ (160 - ) 554 keys would have to be generated before a match would be found. 556 An attacker that wants to match any DS record will have to generate 557 on average at least 2^80 keys. 559 The DS record represents a change to the DNSSEC protocol and there is 560 an installed base of implementations, as well as textbooks on how to 561 set up secure delegations. Implementations that do not understand the 562 DS record will not be able to follow the KEY to DS to KEY chain and 563 will consider all zones secured that way as unsecure. 565 5 IANA Considerations: 567 IANA needs to allocate an RR type code for DS from the standard RR 568 type space (type 43 requested). 570 IANA needs to open a new registry for the DS RR type for digest 571 algorithms. Defined types are: 572 0 is Reserved, 573 1 is SHA-1. 574 Adding new reservations requires IETF standards action. 576 6 Acknowledgments 578 Over the last few years a number of people have contributed ideas 579 that are captured in this document. The core idea of using one key to 580 sign only the KEY RRset comes from discussions with Bill Manning and 581 Perry Metzger on how to put in a single root key in all resolvers. 582 Alexis Yushin, Brian Wellington, Paul Vixie, Jakob Schlyter, Scott 583 Rose, Edward Lewis, Lars-Johan Liman, Matt Larson, Mark Kosters, Dan 584 Massey, Olaf Kolman, Phillip Hallam-Baker, Miek Gieben, Havard 585 Eidnes, Donald Eastlake 3rd., Randy Bush, David Blacka, Steve 586 Bellovin, Rob Austein, Derek Atkins, Roy Arends, Harald Alvestrand, 587 and others have provided useful comments. 589 Normative References: 591 [RFC1035] P. Mockapetris, ``Domain Names - Implementation and 592 Specification'', STD 13, RFC 1035, November 1987. 594 [RFC2181] R. Elz, R. Bush, ``Clarifications to the DNS Specification'', 595 RFC 2181, July 1997. 597 [RFC2535] D. Eastlake, ``Domain Name System Security Extensions'', RFC 598 2535, March 1999. 600 [RFC3008] B. Wellington, ``Domain Name System Security (DNSSEC) Signing 601 Authority'', RFC 3008, November 2000. 603 [RFC3090] E. Lewis `` DNS Security Extension Clarification on Zone 604 Status'', RFC 3090, March 2001. 606 [RFC3225] D. Conrad, ``Indicating Resolver Support of DNSSEC'', RFC 607 3225, December 2001. 609 [RFC3226] O. Gudmundsson, ``DNSSEC and IPv6 A6 aware server/resolver 610 message size requirements'', RFC 3226, December 2001. 612 Author Address 614 Olafur Gudmundsson 615 3826 Legation Street, NW 616 Washington, DC, 20015 617 USA 618 620 Full Copyright Statement 622 Copyright (C) The Internet Society (2002). All Rights Reserved. 624 This document and translations of it may be copied and furnished to 625 others, and derivative works that comment on or otherwise explain it 626 or assist in its implementation may be prepared, copied, published 627 and distributed, in whole or in part, without restriction of any 628 kind, provided that the above copyright notice and this paragraph are 629 included on all such copies and derivative works. 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