idnits 2.17.00 (12 Aug 2021) /tmp/idnits15157/draft-ietf-dnsop-kskroll-sentinel-16.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 1 instance of lines with non-RFC2606-compliant FQDNs in the document. ** The document seems to lack a both a reference to RFC 2119 and the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. RFC 2119 keyword, line 121: '...his mechanism is OPTIONAL to implement...' RFC 2119 keyword, line 122: '..., this mechanism SHOULD be enabled by ...' RFC 2119 keyword, line 123: '...urement. Configuration options MAY be...' RFC 2119 keyword, line 168: '...ers that implement this mechanism MUST...' RFC 2119 keyword, line 221: '...ions is not met, the resolver MUST NOT...' (6 more instances...) Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (October 20, 2018) is 1309 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: 'RFC2119' is mentioned on line 162, but not defined == Missing Reference: 'RFC8174' is mentioned on line 162, but not defined -- Obsolete informational reference (is this intentional?): RFC 7719 (Obsoleted by RFC 8499) Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNSOP G. Huston 3 Internet-Draft J. Damas 4 Intended status: Standards Track APNIC 5 Expires: April 23, 2019 W. Kumari 6 Google 7 October 20, 2018 9 A Root Key Trust Anchor Sentinel for DNSSEC 10 draft-ietf-dnsop-kskroll-sentinel-16 12 Abstract 14 The DNS Security Extensions (DNSSEC) were developed to provide origin 15 authentication and integrity protection for DNS data by using digital 16 signatures. These digital signatures can be verified by building a 17 chain of trust starting from a trust anchor and proceeding down to a 18 particular node in the DNS. This document specifies a mechanism that 19 will allow an end user and third parties to determine the trusted key 20 state for the root key of the resolvers that handle that user's DNS 21 queries. Note that this method is only applicable for determining 22 which keys are in the trust store for the root key. 24 [ This document is being collaborated on in Github at: 25 https://github.com/APNIC-Labs/draft-kskroll-sentinel. The most 26 recent version of the document, open issues, etc should all be 27 available here. The authors (gratefully) accept pull requests. RFC 28 Editor, please remove text in square brackets before publication. ] 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on April 23, 2019. 47 Copyright Notice 49 Copyright (c) 2018 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 65 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 66 2. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 4 67 2.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 5 68 2.2. Special Processing . . . . . . . . . . . . . . . . . . . 5 69 3. Sentinel Tests for a Single DNS Resolver . . . . . . . . . . 6 70 3.1. Forwarders . . . . . . . . . . . . . . . . . . . . . . . 9 71 4. Sentinel Tests for Multiple Resolvers . . . . . . . . . . . . 10 72 4.1. Test Scenario and Objective . . . . . . . . . . . . . . . 10 73 4.2. Test Assumptions . . . . . . . . . . . . . . . . . . . . 10 74 4.3. Test Procedure . . . . . . . . . . . . . . . . . . . . . 11 75 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 76 6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13 77 7. Implementation Experience . . . . . . . . . . . . . . . . . . 13 78 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 79 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 80 10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 15 81 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 82 11.1. Normative References . . . . . . . . . . . . . . . . . . 19 83 11.2. Informative References . . . . . . . . . . . . . . . . . 19 84 Appendix A. Protocol Walkthrough Example . . . . . . . . . . . . 19 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 87 1. Introduction 89 The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and 90 [RFC4035] were developed to provide origin authentication and 91 integrity protection for DNS data by using digital signatures. 92 DNSSEC uses Key Tags to efficiently match signatures to the keys from 93 which they are generated. The Key Tag is a 16-bit value computed 94 from the RDATA of a DNSKEY RR as described in Appendix B of 96 [RFC4034]. RRSIG RRs contain a Key Tag field whose value is equal to 97 the Key Tag of the DNSKEY RR that was used to generate the 98 corresponding signature. 100 This document specifies how security-aware DNS resolvers that perform 101 validation of their responses can respond to certain queries in a 102 manner that allows an agent performing the queries to deduce whether 103 a particular key for the root has been loaded into that resolver's 104 trusted key store. This document also describes a procedure where a 105 collection of resolvers can be tested to determine if at least one of 106 these resolvers has loaded a given key into its trusted key store. 107 These tests can be used to determine whether a certain root zone Key 108 Signing Key (KSK) is ready to be used as a trusted key, within the 109 context of a planned root zone KSK key roll. 111 There are two primary use cases for this mechanism: 113 o Users may wish to ascertain whether their DNS resolution 114 environment's resolver is ready for an upcoming root KSK rollover. 116 o Researchers want to perform Internet-wide studies about the 117 proportion of users who will be negatively impacted by an upcoming 118 root KSK rollover. 120 The mechanism described in this document satisfy the requirements of 121 both these use-cases. This mechanism is OPTIONAL to implement and 122 use. If implemented, this mechanism SHOULD be enabled by default to 123 facilitate Internet-wide measurement. Configuration options MAY be 124 provided to disable the mechanism for reasons of local policy. 126 The KSK sentinel tests described in this document use a test 127 comprising of a set of DNS queries to domain names that have special 128 values for the left-most label. The test relies on recursive 129 resolvers supporting a mechanism that recognises this special name 130 pattern in queries, and under certain defined circumstances will 131 return a DNS SERVFAIL response code (RCODE 2), mimicking the response 132 code that is returned by security-aware resolvers when DNSSEC 133 validation fails. 135 If a browser or operating system is configured with multiple 136 resolvers, and those resolvers have different properties (for 137 example, one performs DNSSEC validation and one does not), the 138 sentinel test described in this document can still be used. The 139 sentinel test makes a number of assumptions about DNS resolution 140 behaviour that may not necessarily hold in all environments; if these 141 assumptions do not hold (such as, for example, requiring the stub 142 resolver to query the next recursive resolver in the locally 143 configured set upon receipt of a SERVFAIL response code) then this 144 test may produce indeterminate or inconsistent results. In some 145 cases where these assumptions do not hold, repeating the same test 146 query set may generate different results. 148 Note that the measurements facilitated by the mechanism described in 149 this document are different from those of [RFC8145]. RFC 8145 relies 150 on resolvers reporting towards the root servers a list of locally 151 cached trust anchors for the root zone. Those reports can be used to 152 infer how many resolvers may be impacted by a KSK roll, but not what 153 the user impact of the KSK roll will be. 155 1.1. Terminology 157 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 158 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 159 "OPTIONAL" in this document are to be interpreted as described in BCP 160 14 [RFC2119] [RFC8174] when, and only when, they appear in all 161 capitals, as shown here. 163 This document contains a number of terms related to the DNS. The 164 current definitions of these terms can be found in [RFC7719]. 166 2. Sentinel Mechanism in Resolvers 168 DNSSEC-Validating resolvers that implement this mechanism MUST 169 perform validation of responses in accordance with the DNSSEC 170 response validation specification [RFC4035]. 172 This sentinel mechanism makes use of two special labels: 174 o root-key-sentinel-is-ta- 176 o root-key-sentinel-not-ta- 178 These labels trigger special processing in the validating DNS 179 resolver when responses from authoritative servers are received. 180 Labels containing "root-key-sentinel-is-ta-" is used to 181 answer the question "Is this the Key Tag of a key which the 182 validating DNS resolver is currently trusting as a trust anchor?" 183 Labels containing "root-key-sentinel-not-ta-" is used to 184 answer the question "Is this the Key Tag of a key which the 185 validating DNS resolver is *not* currently trusting as a trust 186 anchor?". 188 The special labels defined here came after extensive IETF evaluation 189 of alternative patterns and approaches in light of the desired 190 behaviour (sections 2.1, 2.2) within the resolver and the applied 191 testing methodology (section 4.3). As one example, underscore 192 prefixed names were rejected because a number of browsers / operating 193 systems would not fetch them, as they were not viewed as valid 194 "hostnames".Attention was paid to the consideration of local 195 collisions and the reservation of Left Hand Side (LHS) labels of a 196 domain name, and the impact upon zone operators who might desire to 197 use a similarly constructed hostname for a purpose other than as 198 documented here. Therefore, it is important to note that the 199 reservation of the labels in this manner is definitely not considered 200 "best practice". 202 2.1. Preconditions 204 All of the following conditions must be met to trigger special 205 processing inside resolver code: 207 o The DNS response is DNSSEC validated. 209 o The result of validation is "Secure". 211 o The EDNS(0) Checking Disabled (CD) bit in the query is not set. 213 o The QTYPE is either A or AAAA (Query Type value 1 or 28). 215 o The OPCODE is QUERY. 217 o The leftmost label of the original QNAME (the name sent in the 218 Question Section in the original query) is either "root-key- 219 sentinel-is-ta-" or "root-key-sentinel-not-ta-". 221 If any one of the preconditions is not met, the resolver MUST NOT 222 alter the DNS response based on the mechanism in this document. 224 Note that the is specified in the DNS label as unsigned 225 decimal integer (as described in [RFC4034], section 5.3), but zero- 226 padded to five digits (for example, a Key Tag value of 42 would be 227 represented in the label as 00042). The precise specification of the 228 special labels above should be followed exactly. For example, a 229 label that does not include a Key Tag zero-padded to five digits does 230 not match this specification, and should not be processed as if they 231 did -- in other words, such queries should be handled as any other 232 label and not according to Section 2.2. 234 2.2. Special Processing 236 Responses which fulfil all of the preconditions in Section 2.1 237 require special processing, depending on leftmost label in the QNAME. 239 First, the resolver determines if the numerical value of is 240 equal to any of the Key Tag values of an active root zone KSK which 241 is currently trusted by the local resolver and is stored in its store 242 of trusted keys. An active root zone KSK is one which could 243 currently be used for validation (that is, a key that is not in 244 either the AddPend or Revoked state as described in [RFC5011]). 246 Second, the resolver alters the response being sent to the original 247 query based on both the left-most label and the presence of a key 248 with given Key Tag in the trust anchor store. Two labels and two 249 possible states of the corresponding key generate four possible 250 combinations summarized in the table: 252 Label | Key is trusted | Key is not trusted 253 ------------------------------------------------------------------ 254 is-ta | return original answer | return SERVFAIL 255 not-ta | return SERVFAIL | return original answer 257 Instruction "return SERVFAIL" means that the resolver MUST set 258 RCODE=SERVFAIL (value 2) and the ANSWER section of the DNS response 259 MUST be empty, ignoring all other documents which specify content of 260 the ANSWER section. 262 Instruction "return original answer" means that the resolver MUST 263 process the query without any further special processing; that is, 264 exactly as if the mechanism described in this document was not 265 implemented or was disabled. The answer for the A or AAAA query is 266 sent on to the client. 268 3. Sentinel Tests for a Single DNS Resolver 270 This section describes the use of the sentinel detection mechanism 271 against a single DNS recursive resolver in order to determine whether 272 this resolver is using a particular trust anchor to validate DNSSEC- 273 signed responses. 275 Note that the test in this section applies to a single DNS resolver. 276 The test described in Section 4 applies instead to a collection of 277 DNS resolvers, as might be found in the DNS configuration of an end- 278 user environment. 280 The critical aspect of the DNS names used in this mechanism is that 281 they contain the specified label for either the positive and negative 282 test as the left-most label in the query name. 284 The sentinel detection procedure can test a DNS resolver using three 285 queries: 287 o A query name containing the left-most label "root-key-sentinel-is- 288 ta-". This corresponds to a a validly-signed label in 289 the parent zone, so that responses associated with this query name 290 can be authenticated by a DNSSEC-validating resolver. Any 291 validly-signed DNS zone can be used as the parent zone for this 292 test. 294 o A query name containing the left-most label "root-key-sentinel- 295 not-ta-". This is also a validly-signed label. Any 296 validly-signed DNS zone can be used as the parent zone for this 297 test. 299 o A query name that is signed with a DNSSEC signature that cannot be 300 validated (described as a "bogus" RRset in Section 5 of [RFC4033], 301 when, for example, an RRset associated with a label in a zoneis 302 not signed with a valid RRSIG record). 304 The responses received from queries to resolve each of these query 305 names can be evaluated to infer a trust key state of the DNS 306 resolver. 308 An essential assumption here is that this technique relies on 309 security-aware (DNSSEC validating) resolvers responding with a 310 SERVFAIL response code to queries where DNSSEC checking is requested 311 and the response cannot be validated. Note that other issues can 312 also cause a resolver to return SERVFAIL responses, and so the 313 sentinel processing may sometimes result in incorrect or 314 indeterminate conclusions. 316 To describe this process of classification, DNS resolvers are 317 classified by five distinct behavior types using the labels: "Vnew", 318 "Vold", "Vind", "nonV", and "other". These labels correspond to 319 resolver system behaviour types as follows: 321 Vnew: A DNS resolver that is configured to implement this mechanism 322 and has loaded the nominated key into their local trusted key 323 stores will respond with an A or AAAA RRset response for the 324 associated "root-key-sentinel-is-ta" queries, SERVFAIL for "root- 325 key-sentinel-not-ta" queries and SERVFAIL for the signed name 326 queries that return "bogus" validation status. 328 Vold: A DNS resolver that is configured to implement this mechanism 329 and has not loaded the nominated key into their local trusted key 330 stores will respond with an SERVFAIL for the associated "root-key- 331 sentinel-is-ta" queries, an A or AAAA RRset response for "root- 332 key-sentinel-not-ta" queries and SERVFAIL for the signed name 333 queries that return "bogus" validation status. 335 Vind: A DNS resolver that has is not configured to implement this 336 mechanism will respond with an A or AAAA RRset response for "root- 337 key-sentinel-is-ta", an A or AAAA RRset response for "root-key- 338 sentinel-not-ta" and SERVFAIL for the name that returns "bogus" 339 validation status. This set of responses does not give any 340 information about the trust anchors used by this resolver. 342 nonV: A non-security-aware DNS resolver will respond with an A or 343 AAAA RRset response for "root-key-sentinel-is-ta", an A or AAAA 344 RRset response for "root-key-sentinel-not-ta" and an A or AAAA 345 RRset response for the name that returns "bogus" validation 346 status. 348 other: There is the potential to admit other combinations of 349 responses to these three queries. While this may appear self- 350 contradictory, there are cases where such an outcome is possible. 351 For example, in DNS resolver farms what appears to be a single DNS 352 resolver that responds to queries passed to a single IP address is 353 in fact constructed as a a collection of slave resolvers, and the 354 query is passed to one of these internal resolver engines. If 355 these individual slave resolvers in the farm do not behave 356 identically, then other sets of results can be expected from these 357 three queries. In such a case, no determination about the 358 capabilities of this DNS resolver farm can be made. 360 Note that SERVFAIL might be cached according to Section 7 of 361 [RFC2308] for up to 5 minutes and a positive answer for up to its 362 TTL. 364 If a client directs these three queries to a single resolver, the 365 responses should allow the client to determine the capability of the 366 resolver, and if it supports this sentinel mechanism, whether or not 367 it has a particular key in its trust anchor store, as in the 368 following table: 370 Query 371 +----------+-----------+------------+ 372 | is-ta | not-ta | bogus | 373 +-------+----------+-----------+------------+ 374 | Vnew | Y | SERVFAIL | SERVFAIL | 375 | Vold | SERVFAIL | Y | SERVFAIL | 376 Type | Vind | Y | Y | SERVFAIL | 377 | nonV | Y | Y | Y | 378 | other | * | * | * | 379 +-------+----------+-----------+------------+ 381 In this table the 'Y' response denotes an A or AAAA RRset response 382 (depending on the Query Type of A or AAAA records), 'SERVFAIL' 383 denotes a DNS SERVFAIL response code (RCODE 2), and '*' denotes 384 either response. 386 Vnew: The nominated key is trusted by the resolver. 388 Vold: The nominated key is not yet trusted by the resolver. 390 Vind: There is no information about the trust anchors of the 391 resolver. 393 nonV: The resolver does not perform DNSSEC validation. 395 other: The properties of the resolver cannot be analyzed by this 396 protocol. 398 3.1. Forwarders 400 Some resolvers are configured not to answer queries using the 401 recursive algorithm first described in [RFC1034] section 4.3.2, but 402 instead relay queries to one or more other resolvers. Resolvers 403 configured in this manner are referred to in this document as 404 "forwarders". 406 If the resolver is non-validating, and it has a single forwarder, 407 then the resolver will presumably mirror the capabilities of the 408 forwarder's target resolver. 410 If the validating resolver has a forwarding configuration, and it 411 sets the EDNS(0) Checking Disabled (CD) bit as described in 412 Section 3.2.2 of [RFC4035] on all forwarded queries, then this 413 resolver is acting in a manner that is identical to a standalone 414 resolver. 416 A more complex case is where all of the following conditions hold: 418 o Both the validating resolver and the forwarder target resolver 419 support this trusted key sentinel mechanism 421 o The local resolver's queries do not have the EDNS(0) CD bit set 423 o The trusted key state differs between the forwarding resolver and 424 the forwarder's target resolver 426 In such a case, either the outcome is indeterminate validating 427 ("Vind"), or a case of mixed signals such as SERVFAIL in all three 428 responses, ("other") which is similarly an indeterminate response 429 with respect to the trusted key state. 431 4. Sentinel Tests for Multiple Resolvers 433 The description in Section 3 describes a trust anchor test that can 434 be used in the simple situation where the test queries were being 435 passed to a single recursive resolver that directly queried 436 authoritative name servers. 438 However, the common end-user scenario is where a user's local DNS 439 resolution environment is configured to use more than one recursive 440 resolver. The single resolver test technique will not function 441 reliably in such cases, as a a SERVFAIL response from one resolver 442 may cause the local stub resolver to repeat the query against one of 443 the other configured resolvers and the results may be inconclusive. 445 In describing a test procedure that can be used in this environment 446 of a set of DNS resolvers there are some necessary changes to the 447 nature of the question that this test can answer, the assumptions 448 about the behaviour of the DNS resolution environment, and some 449 further observations about potential variability in the test 450 outcomes. 452 4.1. Test Scenario and Objective 454 This test is not intended to expose which trust anchors are used by 455 any single DNS resolver. 457 The test scenario is explicitly restricted to that of the KSK 458 environment where a current active KSK (called "KSK-current") is to 459 be replaced with a new KSK (called "KSK-new"). The test is designed 460 to be run between when KSK-new is introduced into the root zone and 461 when the root zone is signed with KSK-new. 463 The objective of the test is to determine if the user will be 464 negatively impacted by the KSK roll. A "negative impact" for the 465 user is defined such that all the configured resolvers are security- 466 aware resolvers that perform validation of DNSSEC-signed responses, 467 and none of these resolvers have loaded KSK-new into their local 468 trust anchor set. In this situation, it is anticipated that once the 469 KSK is rolled the entire set of the user's resolvers will not be able 470 to validate the contents of the root zone and the user is likely to 471 lose DNS service as a result of this inability to perform successful 472 DNSSEC validation. 474 4.2. Test Assumptions 476 There are a number of assumptions about the DNS environment used in 477 this test. Where these assumptions do not hold, the results of the 478 test will be indeterminate. 480 o When a recursive resolver returns SERVFAIL to the user's stub 481 resolver, the stub resolver will send the same query to the next 482 resolver in the locally configured resolver set. It will continue 483 to do this until it gets a non-SERVFAIL response or until it runs 484 out of resolvers to try. 486 o When the user's stub resolver passes a query to a resolver in the 487 configured resolver set, it will get a consistent answer over the 488 timeframe of the queries. This assumption implies that if the 489 same query is asked by the same stub resolver multiple times in 490 succession to the same recursive resolver, the recursive 491 resolver's response will be the same for each of these queries. 493 o All DNSSEC-validating resolvers have KSK-current in their local 494 trust anchor cache. 496 There is no current published measurement data that indicates to what 497 extent the first two assumptions listed here are valid, and how many 498 end users may be impacted by these assumptions. In particular, the 499 first assumption, that a consistent SERFAIL response will cause the 500 local stub DNS resolution environment to query all of its configured 501 recursive resolvers before concluding that the name cannot be 502 resolved, is a very critical assumption for this test. 504 Note that additional precision / determinism may be achievable by 505 bypassing the normal OS behavior and explicitly testing using each 506 configured recursive resolver (e.g using 'dig'). 508 4.3. Test Procedure 510 The sentinel detection process tests a DNS resolution environment 511 with three query names. Note that these same general categories of 512 query as in Section 3 but the key tag used is different for some 513 queries: 515 o A query name that is signed with a DNSSEC signature that cannot be 516 validated (described as a "bogus" RRset in Section 5 of [RFC4033], 517 when, for example, an RRset is not signed with a valid RRSIG 518 record). 520 o A query name containing the left-most label "root-key-sentinel- 521 not-ta-". This name MUST be a validly- 522 signed name. Any validly-signed DNS zone can be used for this 523 test. 525 o A query name containing the left-most label "root-key-sentinel-is- 526 ta-". This name MUST be a validly-signed 527 name. Any validly-signed DNS zone can be used for this test. 529 The responses received from queries to resolve each of these names 530 can be evaluated to infer a trust key state of the user's DNS 531 resolution environment. 533 The responses to these queries are described using a simplified 534 notation. Each query will either result in a SERFVAIL response 535 (denoted as "S"), indicating that all of the resolvers in the 536 recursive resolver set returned the SERVFAIL response code, or result 537 in a response with the desire RRset value (denoted as "A"). The 538 queries are ordered by the "invalid" name, the "root-key-sentinel- 539 not-ta" label, then the "root-key-sentinel-is-ta" label, and a 540 triplet notation denotes a particular response. For example, the 541 triplet "(S S A)" denotes a SERVFAIL response to the invalid query, a 542 SERVFAIL response to the "root-key-sentinel-not-ta" query and a RRset 543 response to the "root-key-sentinel-is-ta" query. 545 The set of all possible responses to these three queries are: 547 (A * *): If any resolver returns an "A" response for the query for 548 the invalid name, then the resolver set contains at least one non- 549 validating DNS resolver, and the user will not be impacted by the 550 KSK roll. 552 (S A *): If any of the resolvers returns an "A" response the the 553 "root-key-sentinel-not-ta" query, then at least one of the 554 resolvers does not recognise the sentinel mechanism, and the 555 behaviour of the collection of resolvers during the KSK roll 556 cannot be reliably determined. 558 (S S A): This case implies that all of the resolvers in the set 559 perform DNSSEC-validation, all of the resolvers are aware of the 560 sentinel mechanism, and at least one resolver has loaded KSK-new 561 as a local trust anchor. The user will not be impacted by the KSK 562 roll. 564 (S S S): This case implies that all of the resolvers in the set 565 perform DNSSEC-validation, all of the resolvers are aware of the 566 sentinel mechanism, and none of the resolvers has loaded KSK-new 567 as a local trust anchor. The user will be negatively impacted by 568 the KSK roll. 570 5. Security Considerations 572 This document describes a mechanism to allow users to determine the 573 trust anchor state of root zone key signing keys in the DNS 574 resolution system that they use. If the user executes third party 575 code, then this information may also be available to the third party. 577 The mechanism does not require resolvers to set otherwise 578 unauthenticated responses to be marked as authenticated, and does not 579 alter the security properties of DNSSEC with respect to the 580 interpretation of the authenticity of responses that are so marked. 582 The mechanism does not require any further significant processing of 583 DNS responses, and queries of the form described in this document do 584 not impose any additional load that could be exploited in an attack 585 over the normal DNSSEC validation processing load. 587 6. Privacy Considerations 589 The mechanism in this document enables third parties (with either 590 good or bad intentions) to learn something about the security 591 configuration of recursive DNS resolvers. That is, someone who can 592 cause an Internet user to make specific DNS queries (e.g. via web- 593 based advertisements or javascript in web pages), can, under certain 594 specific circumstances that includes additional knowledge of the 595 resolvers that are invoked by the user, determine which trust anchors 596 are configured in these resolvers. Without this additional 597 knowledge, the third party can infer the aggregate capabilities of 598 the user's DNS resolution environment, but cannot necessarily infer 599 the trust configuration of any recursive name server. 601 7. Implementation Experience 603 [ RFC Editor: Please remove before publication. As this section will 604 be removed, it is more conversational than would appear in a 605 published doc. ] 607 List of known resolver implementations (alphabetical): 609 BIND Ondrej Sury of ISC reported to the DNSOP Working Group in 610 April 2018 that this technique was peer-reviewed and merged into 611 BIND master branch with the intent to backport the feature into 612 older release branches. The merge request: 613 https://gitlab.isc.org/isc-projects/bind9/merge_requests/123 614 Information on configuring this can be found in the BIND 9.13.0 615 Administrator Reference Manual (ARM), available at 616 https://ftp.isc.org/isc/bind9/9.13.0/doc/arm/Bv9ARM.pdf 618 Knot resolver Petr Spacek implemented early versions of this 619 technique into the Knot resolver, identified a number of places 620 where it wasn't clear, and provided very helpful text to address 621 these issues and make the document mode clear. Petr also 622 identified an embarrassingly large number of typos (and similar) 623 in the ksk-test setup. More information is at http://knot- 624 resolver.readthedocs.io/en/stable/modules.html#sentinel-for- 625 detecting-trusted-keys 627 Unbound Benno Overeinder of NLnet Labs reported to the DNSOP Working 628 Group in April 2018 an intention to support this technique in 629 Unbound in the near future. This is now implemented in Unbound 630 version 1.7.1, available from http://unbound.nlnetlabs.nl/ 631 download.html . Configuration information is at 632 http://unbound.nlnetlabs.nl/documentation/unbound.conf.html 634 A (partial) list of "client" / user side implementations (the author 635 was keeping a more complete list of implementations, but has 636 misplaced it - apologies, I'm happy to re-add them if you send me a 637 note.): 639 http://www.ksk-test.net An Javascript implementation of the client 640 side of this protocol is available at: http://www.ksk-test.net 642 http://test.kskroll.dnssec.lab.nic.cl/ Hugo Salgado-Hernandez has 643 created an implementation at 644 http://test.kskroll.dnssec.lab.nic.cl/ 646 http://sentinel.research.icann.org/ The code for this implementation 647 is published at https://github.com/paulehoffman/sentinel-testbed 649 http://www.bellis.me.uk/sentinel/ Ray Bellis client implementation - 650 http://www.bellis.me.uk/sentinel/ 652 8. IANA Considerations 654 This document has no IANA actions. 656 9. Acknowledgements 658 This document has borrowed extensively from [RFC8145] for the 659 introductory text, and the authors would like to acknowledge and 660 thank the authors of that document both for some text excerpts and 661 for the more general stimulation of thoughts about monitoring the 662 progress of a roll of the KSK of the root zone of the DNS. 664 The authors would like to thank Joe Abley, Mehmet Akcin, Mark 665 Andrews, Richard Barnes, Ray Bellis, Stephane Bortzmeyer, David 666 Conrad, Ralph Dolmans, John Dickinson, Steinar Haug, Bob Harold, Wes 667 Hardaker, Paul Hoffman, Matt Larson, Jinmei Tatuya, Edward Lewis, 668 George Michaelson, Benno Overeinder, Matthew Pounsett, Hugo Salgado- 669 Hernandez, Andreas Schulze, Mukund Sivaraman, Petr Spacek, Job 670 Snijders, Andrew Sullivan, Ondrej Sury, Paul Vixie, Duane Wessels and 671 Paul Wouters for their helpful feedback. 673 The authors would like to especially call out Paul Hoffman and Duane 674 Wessels for providing comments in the form of pull requests. Joe 675 Abley also helpfully provided extensive review and OLD / NEW text. 677 Petr Spacek wrote some very early implementations, and provided 678 significant feedback (including pointing out when the test bed didn't 679 match the document!) 681 10. Change Log 683 RFC Editor: Please remove this section! 685 Note that this document is being worked on in GitHub - see Abstract. 686 The below is mainly large changes, and is not authoritative. 688 From -15 to -16: 690 o Addressed IESG comments 692 o Benjamin Kaduk's Discuss on draft-ietf-dnsop-kskroll-sentinel 694 o Also added Terry's "This a bad design pattern, but we decided the 695 benefits outweigh the costs this time." text. 697 o Suggestion from Adam to clarify that bypassing e.g gethostbyname() 698 can provide better testing. 700 o Nit: Forgot 'name' in 'This name MUST be a validly-signed name.' 702 o Clarified that 'bogus.example.com' is intentionally DNSSEC bogus / 703 invalid. 705 From -14 to -15: 707 o Addressed Joe Abley's thorough review, at: 708 https://mailarchive.ietf.org/arch/msg/dnsop/8ZnN1xj55Yimet2cg- 709 LrdoJafEA 711 From -13 to -14: 713 o Addressed nits from Bob Harold - 714 https://mailarchive.ietf.org/arch/msg/dnsop/ 715 j4Serw0z24o470AnlD8ISo8o9k4 717 o Formatting changes (and a bit more text) in the implementation 718 section. 720 o Closes PR #21: Clarify indeterminate and resolution systems, 721 o Closes PR #22: Updates to -13 describing the test procedure for a 722 set of resolvers 724 o Closes PR #23: Fix sundry typos, 726 o Closes PR #24: Editorial and clarifications to the new text 728 o Closes PR #25: Clarified when the test can be run 730 From -12 to -13: 732 o Merged Paul Hoffmans PR#19, PR#20. 734 o Moved toy ksk-test.net to implementation section. 736 o Split the test procedures between the test of a single DNS 737 resolvers and the test of a collection of DNS resolvers as would 738 be found in an end user environment. 740 From -11 to -12: 742 o Moved the Walkthrough Example to the end of the document as an 743 appendix. 745 o Incorporated changes as proposed by Ondrej Sury, relating to a 746 consistent use of Key Tag and a reference to the definition of a 747 Bogus RRset. 749 o Corrected minor typos. 751 o Revised the Privacy Considerations. 753 o In response to a request from DNSOP Working Group chairs, a 754 section on reported Implementation Experience has been added, 755 based on postings to the DNSOP Working Group mailing list. 757 From -10 to -11: 759 o Clarified the preconditions for this mechanism as per Working 760 Group mailing list discussion. 762 o Corrected minor typo. 764 From -09 to -10: 766 o Clarified the precondition list to specify that the resolver had 767 performed DNSSEC-validation by setting the AD bit in the response 769 o Clarified the language referring to the operation of RFC8145 770 signalling. 772 From -08 to -09: 774 o Incorporated Paul Hoffman's PR # 15 (Two issues from the 775 Hackathon) - https://github.com/APNIC-Labs/draft-kskroll-sentinel/ 776 pull/15 778 o Clarifies that the match is on the *original* QNAME. 780 From -08 to -07: 782 o Changed title from "A Sentinel for Detecting Trusted Keys in 783 DNSSEC" to "A Root Key Trust Anchor Sentinel for DNSSEC". 785 o Changed magic string from "kskroll-sentinel-" to "root-key- 786 sentinel-" -- this time for sure, Rocky! 788 From -07 to -06: 790 o Addressed GitHub PR #14: Clarifications regarding caching and 791 SERVFAIL responses 793 o Addressed GitHub PR #12, #13: Clarify situation with multiple 794 resolvers, Fix editorial nits. 796 From -05 to -06: 798 o Paul improved my merging of Petr's text to make it more readable. 799 Minor change, but this is just before the cut-off, so I wanted it 800 maximally readable. 802 From -04 to -05: 804 o Incorporated Duane's #10 806 o Integrated Petr Spacek's Issue - https://github.com/APNIC-Labs/ 807 draft-kskroll-sentinel/issues/9 (note that commit-log incorrectly 808 referred to Duane's PR as number 9, it is actually 10). 810 From -03 to -04: 812 o Addressed GitHub pull requests #4, #5, #6, #7 #8. 814 o Added Duane's privacy concerns 816 o Makes the use cases clearer 817 o Fixed some A/AAAA stuff 819 o Changed the example numbers 821 o Made it clear that names and addresses must be real 823 From -02 to -03: 825 o Integrated / published comments from Paul in GitHub PR #2 - 826 https://github.com/APNIC-Labs/draft-kskroll-sentinel/pull/2 828 o Made the Key Tag be decimal, not hex (thread / consensus in 829 https://mailarchive.ietf.org/arch/msg/dnsop/ 830 Kg7AtDhFRNw31He8n0_bMr9hBuE ) 832 From -01 to 02: 834 o Removed Address Record definition. 836 o Clarified that many things can cause SERVFAIL. 838 o Made examples FQDN. 840 o Fixed a number of typos. 842 o Had accidentally said that Charlie was using a non-validating 843 resolver in example. 845 o [ TODO(WK): Doc says Key Tags are hex, is this really what the WG 846 wants? ] 848 o And active key is one that can be used *now* (not e.g AddPend) 850 From -00 to 01: 852 o Added a conversational description of how the system is intended 853 to work. 855 o Clarification that this is for the root. 857 o Changed the label template from _is-ta- to kskroll- 858 sentinel-is-ta-. This is because BIND (at least) will 859 not allow records which start with an underscore to have address 860 records (CNAMEs, yes, A/AAAA no). Some browsers / operating 861 systems also will not fetch resources from names which start with 862 an underscore. 864 11. References 866 11.1. Normative References 868 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 869 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 870 . 872 [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS 873 NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998, 874 . 876 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 877 Rose, "DNS Security Introduction and Requirements", 878 RFC 4033, DOI 10.17487/RFC4033, March 2005, 879 . 881 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 882 Rose, "Resource Records for the DNS Security Extensions", 883 RFC 4034, DOI 10.17487/RFC4034, March 2005, 884 . 886 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 887 Rose, "Protocol Modifications for the DNS Security 888 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 889 . 891 [RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC) 892 Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011, 893 September 2007, . 895 11.2. Informative References 897 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 898 Terminology", RFC 7719, DOI 10.17487/RFC7719, December 899 2015, . 901 [RFC8145] Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust 902 Anchor Knowledge in DNS Security Extensions (DNSSEC)", 903 RFC 8145, DOI 10.17487/RFC8145, April 2017, 904 . 906 Appendix A. Protocol Walkthrough Example 908 This Appendix provides a non-normative example of how the sentinel 909 mechanism could be used, and what each participant does. It is 910 provided in a conversational tone to be easier to follow. The 911 examples here all assume that each person has just one resolver, or a 912 system of resolvers that have the same properties. 914 Alice is in charge of the DNS root KSK (Key Signing Key), and would 915 like to roll / replace the key with a new one. She publishes the new 916 KSK, but would like to be able to predict / measure what the impact 917 will be before removing/revoking the old key. The current KSK has a 918 Key Tag of 11112, the new KSK has a Key Tag of 02323. Users want to 919 verify that their resolver will not break after Alice rolls the root 920 KSK key (that is, starts signing with just the KSK whose Key Tag is 921 02323). 923 Bob, Charlie, Dave, Ed are all users. They use the DNS recursive 924 resolvers supplied by their ISPs. They would like to confirm that 925 their ISPs have picked up the new KSK. Bob's ISP does not perform 926 validation. Charlie's ISP does validate, but the resolvers have not 927 yet been upgraded to support this mechanism. Dave and Ed's resolvers 928 have been upgraded to support this mechanism; Dave's resolver has the 929 new KSK, Ed's resolver hasn't managed to install the 02323 KSK in its 930 trust store yet. 932 Geoff is a researcher, and would like to both provide a means for 933 Bob, Charlie, Dave and Ed to be able to perform tests, and also would 934 like to be able to perform Internet-wide measurements of what the 935 impact will be (and report this back to Alice). 937 Geoff sets an authoritative DNS server for example.com, and also a 938 webserver (www.example.com). He adds three address records to 939 example.com: 941 bogus.example.com. IN AAAA 2001:db8::1 943 root-key-sentinel-is-ta-02323.example.com. IN AAAA 2001:db8::1 945 root-key-sentinel-not-ta-11112.example.com. IN AAAA 2001:db8::1 947 Note that the use of "example.com" names and the addresses here are 948 examples, and 'bogus' intentionally has invalid DNSSEC signatures. 949 In a real deployment, the domain names need to be under control of 950 the researcher, and the addresses must be real, reachable addresses. 952 Geoff then DNSSEC signs the example.com zone, and intentionally makes 953 the bogus.example.com record have bogus validation status (for 954 example, by editing the signed zone and entering garbage for the 955 signature). Geoff also configures his webserver to listen on 956 2001:db8::1 and serve a resource (for example, a 1x1 GIF, 1x1.gif) 957 for all of these names. The webserver also serves a webpage 958 (www.example.com) which contains links to these 3 resources 959 (http://bogus.example.com/1x1.gif, http://root-key-sentinel-is-ta- 960 02323.example.com/1x1.gif, http://root-key-sentinel-not-ta- 961 11112.example.com/1x1.gif). 963 Geoff then asks Bob, Charlie, Dave and Ed to browse to 964 www.example.com. Using the methods described in this document, the 965 users can figure out what their fate will be when the 11112 KSK is 966 removed. 968 Bob is not using a validating resolver. This means that he will be 969 able to resolve bogus.example.com (and fetch the 1x1 GIF) - this 970 tells him that the KSK roll does not affect him, and so he will be 971 OK. 973 Charlie's resolvers are validating, but they have not been upgraded 974 to support the KSK sentinel mechanism. Charlie will not be able to 975 fetch the http://bogus.example.com/1x1.gif resource (the 976 bogus.example.com record is bogus, and none of his resolvers will 977 resolve it). He is able to fetch both of the other resources - from 978 this he knows (see the logic in the body of this document) that he is 979 using validating resolvers, but at least one of these resolvers is 980 not configured to perform sentinel processing. The KSK sentinel 981 method cannot provide him with a definitive answer to the question of 982 whether he will be impacted by the KSK roll. 984 Dave's resolvers implement the sentinel method, and have picked up 985 the new KSK. For the same reason as Charlie, he cannot fetch the 986 "bogus" resource. His resolver resolves the root-key-sentinel-is-ta- 987 02323.example.com name normally (it contacts the example.com 988 authoritative servers, etc); as it supports the sentinel mechanism, 989 just before Dave's recursive resolver sends the reply to Dave's stub, 990 it performs the KSK Sentinel check. The QNAME starts with "root-key- 991 sentinel-is-ta-", and the recursive resolver does indeed have a key 992 with the Key Tag of 02323 in its root trust store. This means that 993 that this part of the KSK Sentinel check passes (it is true that Key 994 Tag 02323 is in the trust anchor store), and the recursive resolver 995 replies normally (with the answer provided by the authoritative 996 server). Dave's recursive resolver then resolves the root-key- 997 sentinel-not-ta-11112.example.com name. Once again, it performs the 998 normal resolution process, but because it implements KSK Sentinel 999 (and the QNAME starts with "root-key-sentinel-not-ta-"), just before 1000 sending the reply, it performs the KSK Sentinel check. As it has the 1001 key with key-tag 11112 in it's trust anchor store, the answer to "is 1002 this *not* a trust anchor" is false, and so the recursive resolver 1003 does not reply with the answer from the authoritative server - 1004 instead, it replies with a SERVFAIL (note that replying with SERVFAIL 1005 instead of the original answer is the only mechanism that KSK 1006 Sentinel uses). This means that Dave cannot fetch "bogus", he can 1007 fetch "root-key-sentinel-is-ta-02323", but he cannot fetch "root-key- 1008 sentinel-not-ta-11112". From this, Dave knows that he is behind an 1009 collection of resolvers that all validate, all have the key with key 1010 tag 11112 loaded and at least one of these resolvers has loaded the 1011 key with key-tag 02323 into its local trust anchor cache, Dave will 1012 not be impacted by the KSK roll. 1014 Just like Charlie and Dave, Ed cannot fetch the "bogus" record. This 1015 tells him that his resolvers are validating. When his (sentinel- 1016 aware) resolvers performs the KSK Sentinel check for "root-key- 1017 sentinel-is-ta-02323", none of them have loaded the new key with key- 1018 tag 02323 in their local trust anchor store. This means check fails, 1019 and Ed's recursive resolver converts the (valid) answer into a 1020 SERVFAIL error response. It performs the same check for root-key- 1021 sentinel-not-ta-11112.example.com, and as all of Ed's resolvers both 1022 perform DNSSEC validation and recognise the sentinel label Ed will be 1023 unable to fetch the "root-key-sentinel-not-ta-11112" resource. This 1024 tells Ed that his resolvers have not installed the new KSK and he 1025 will be negatively implacted by the KSK roll.. 1027 Geoff would like to do a large scale test and provide the information 1028 back to Alice. He uses some mechanism such as causing users to go to 1029 a web page to cause a large number of users to attempt to resolve the 1030 three resources, and then analyzes the results of the tests to 1031 determine what percentage of users will be affected by the KSK 1032 rollover event. 1034 This description is a simplified example - it is not anticipated that 1035 Bob, Charlie, Dave and Ed will actually look for the absence or 1036 presence of web resources; instead, the webpage that they load would 1037 likely contain JavaScript (or similar) which displays the result of 1038 the tests, sends the results to Geoff, or both. This sentinel 1039 mechanism does not rely on the web: it can equally be used by trying 1040 to resolve the names (for example, using the common "dig" command) 1041 and checking which result in a SERVFAIL. 1043 Authors' Addresses 1045 Geoff Huston 1047 Email: gih@apnic.net 1048 URI: http://www.apnic.net 1050 Joao Silva Damas 1052 Email: joao@apnic.net 1053 URI: http://www.apnic.net 1054 Warren Kumari 1056 Email: warren@kumari.net