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Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 6485 (Obsoleted by RFC 7935) ** Obsolete normative reference: RFC 6486 (Obsoleted by RFC 9286) ** Obsolete normative reference: RFC 7730 (Obsoleted by RFC 8630) Summary: 3 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SIDR Operations O. Muravskiy 3 Internet-Draft RIPE NCC 4 Intended status: Informational T. Bruijnzeels 5 Expires: December 30, 2018 NLNetLabs 6 June 28, 2018 8 RPKI Certificate Tree Validation by the RIPE NCC RPKI Validator 9 draft-ietf-sidrops-rpki-tree-validation-02 11 Abstract 13 This document describes the approach to validate the content of the 14 RPKI certificate tree, as it is implemented in the RIPE NCC RPKI 15 Validator. This approach is independent of a particular object 16 retrieval mechanism. This allows it to be used with repositories 17 available over the rsync protocol, the RPKI Repository Delta 18 Protocol, and repositories that use a mix of both. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on December 30, 2018. 37 Copyright Notice 39 Copyright (c) 2018 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (https://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Scope of this document . . . . . . . . . . . . . . . . . . . 3 55 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 56 3. General Considerations . . . . . . . . . . . . . . . . . . . 4 57 3.1. Hash comparisons . . . . . . . . . . . . . . . . . . . . 4 58 3.2. Discovery of RPKI objects issued by a CA . . . . . . . . 4 59 3.3. Manifest entries versus repository content . . . . . . . 4 60 4. Top-down Validation of a Single Trust Anchor Certificate Tree 5 61 4.1. Fetching the Trust Anchor Certificate Using the Trust 62 Anchor Locator . . . . . . . . . . . . . . . . . . . . . 5 63 4.2. CA Certificate Validation . . . . . . . . . . . . . . . . 6 64 4.2.1. Finding the most recent valid manifest and CRL . . . 7 65 4.2.2. Manifest entries validation . . . . . . . . . . . . . 8 66 4.3. Object Store Cleanup . . . . . . . . . . . . . . . . . . 9 67 5. Remote Objects Fetcher . . . . . . . . . . . . . . . . . . . 9 68 5.1. Fetcher Operations . . . . . . . . . . . . . . . . . . . 9 69 5.1.1. Fetch repository objects . . . . . . . . . . . . . . 10 70 5.1.2. Fetch single repository object . . . . . . . . . . . 10 71 6. Local Object Store . . . . . . . . . . . . . . . . . . . . . 11 72 6.1. Store Operations . . . . . . . . . . . . . . . . . . . . 11 73 6.1.1. Store Repository Object . . . . . . . . . . . . . . . 11 74 6.1.2. Get objects by hash . . . . . . . . . . . . . . . . . 11 75 6.1.3. Get certificate objects by URI . . . . . . . . . . . 11 76 6.1.4. Get manifest objects by AKI . . . . . . . . . . . . . 11 77 6.1.5. Delete objects for a URI . . . . . . . . . . . . . . 12 78 6.1.6. Delete outdated objects . . . . . . . . . . . . . . . 12 79 6.1.7. Update object's validation time . . . . . . . . . . . 12 80 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 81 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 82 9. Security Considerations . . . . . . . . . . . . . . . . . . . 12 83 9.1. Hash collisions . . . . . . . . . . . . . . . . . . . . . 12 84 9.2. Mismatch between the expected and the actual location of 85 an object in the repository . . . . . . . . . . . . . . . 12 86 9.3. Manifest content versus publication point content . . . . 13 87 9.4. Storing of a TA certificate object before its complete 88 validation . . . . . . . . . . . . . . . . . . . . . . . 13 89 9.5. Possible denial of service . . . . . . . . . . . . . . . 14 90 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 91 10.1. Normative References . . . . . . . . . . . . . . . . . . 14 92 10.2. Informative References . . . . . . . . . . . . . . . . . 15 93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 95 1. Scope of this document 97 This document describes how the RIPE NCC RPKI Validator version 2.23 98 has been implemented. Source code to this software can be found at 99 [github]. The purpose of this document is to provide transparency to 100 users of (and contributors to) this software tool, as well as serve 101 to be subjected to scrutiny by the SIDR Operations Working Group. It 102 is not intended as a document that describes a standard or best 103 practices on how validation should be done in general. 105 2. Introduction 107 In order to use information published in RPKI repositories, Relying 108 Parties (RP) need to retrieve and validate the content of 109 certificates, certificate revocation lists (CRLs), and other RPKI 110 signed objects. To validate a particular object, one must ensure 111 that all certificates in the certificate chain up to the Trust Anchor 112 (TA) are valid. Therefore the validation of a certificate tree is 113 performed top-down, starting from the TA certificate and descending 114 down the certificate chain, validating every encountered certificate 115 and its products. The result of this process is a list of all 116 encountered RPKI objects with a validity status attached to each of 117 them. These results may later be used by a Relying Party in taking 118 routing decisions, etc. 120 Traditionally RPKI data is made available to RPs through the 121 repositories [RFC6481] accessible over [rsync] protocol. Relying 122 parties are advised to keep a local copy of repository data, and 123 perform regular updates of this copy from the repository (Section 5 124 of [RFC6481]). The RPKI Repository Delta Protocol 125 [I-D.ietf-sidr-delta-protocol] introduces another method to fetch 126 repository data and keep the local copy up to date with the 127 repository. 129 This document describes how the RIPE NCC RPKI Validator discovers 130 RPKI objects to download, builds certificate paths, and validates 131 RPKI objects, independently from what repository access protocol is 132 used. To achieve this, it puts downloaded RPKI objects in an object 133 store, where each RPKI object can be found by its URI, the hash of 134 its content, value of its Authority Key Identifier (AKI) extension, 135 or a combination of these. It also keeps track of the download and 136 the validation time for every object, to decide which locally stored 137 objects are not used in the RPKI tree validation and could be 138 removed. 140 3. General Considerations 142 3.1. Hash comparisons 144 This algorithm relies on the properties of the file hash algorithm 145 (defined in [RFC6485]) to compute the hash of repository objects. It 146 assumes that any two objects for which the hash value is the same, 147 are identical. 149 The hash comparison is used when matching objects in the repository 150 with entries on the manifest (Section 4.2.2), and when looking up 151 objects in the object store (Section 6). 153 3.2. Discovery of RPKI objects issued by a CA 155 There are several possible ways of discovering products of a CA 156 certificate: one could use all objects located in a repository 157 directory designated as a publication point for a CA, or only objects 158 mentioned on the manifest located at that publication point (see 159 Section 6 of [RFC6486]), or use all objects whose AKI extension 160 matches the Subject Key Identifier (SKI) extension (Section 4.2.1 of 161 [RFC5280]) of a CA certificate. 163 For publication points whose content is consistent with the manifest 164 and issuing certificate all of these approaches should produce the 165 same result. For inconsistent publication points the results might 166 be different. Section 6 of [RFC6486] leaves the decision on how to 167 deal with inconsistencies to a local policy. 169 The implementation described here does not rely on content of 170 repository directories, but uses the Authority Key Identifier (AKI) 171 extension of a manifest and a certificate revocation list (CRL) to 172 find in an object store (Section 6) a manifest and a CRL issued by a 173 particular Certification Authority (CA) (see Section 4.2.1). It 174 further uses the hashes of manifest's fileList entries (Section 4.2.1 175 of [RFC6486]) to find other objects issued by the CA, as described in 176 Section 4.2.2. 178 3.3. Manifest entries versus repository content 180 Since the current set of RPKI standards requires use of the manifest 181 [RFC6486] to describe the content of a publication point, this 182 implementation requires strict consistency between the publication 183 point content and manifest content. (This is a more stringent 184 requirement than established in [RFC6486].) Therefore it will not 185 process objects that are found in the publication point but do not 186 match any of the entries of that publication point's manifest (see 187 Section 4.2.2). It will also issue warnings for all found 188 mismatches, so that the responsible operators could be made aware of 189 inconsistencies and fix them. 191 4. Top-down Validation of a Single Trust Anchor Certificate Tree 193 1. The validation of a Trust Anchor (TA) certificate tree starts 194 from its TA certificate. To retrieve the TA certificate, a Trust 195 Anchor Locator (TAL) object is used, as described in Section 4.1. 197 2. If the TA certificate is retrieved, it is validated according to 198 Section 7 of [RFC6487] and Section 2.2 of [RFC7730]. Otherwise 199 the validation of certificate tree is aborted and an error is 200 issued. 202 3. If the TA certificate is valid, then all its subordinate objects 203 are validated as described in Section 4.2. Otherwise the 204 validation of certificate tree is aborted and an error is issued. 206 4. For each repository object that was validated during this 207 validation run, its validation timestamp is updated in the object 208 store (see Section 6.1.7). 210 5. Outdated objects are removed from the store as described in 211 Section 4.3. This completes the validation of the TA certificate 212 tree. 214 4.1. Fetching the Trust Anchor Certificate Using the Trust Anchor 215 Locator 217 The following steps are performed in order to fetch a Trust Anchor 218 Certificate: 220 1. (Optional) If the Trust Anchor Locator contains a "prefetch.uris" 221 field, pass the URIs contained in that field to the fetcher (see 222 Section 5.1.1). (This field is a non-standard addition to the 223 TAL format. It helps fetching non-hierarchical rsync 224 repositories more efficiently.) 226 2. Extract the first TA certificate URI from the TAL's URI section 227 (see Section 2.1 of [RFC7730]) and pass it to the object fetcher 228 (Section 5.1.2). If the fetcher returns an error, repeat this 229 step for every URI in the URI section, until no error is 230 encountered, or no more URIs left. 232 3. Retrieve from the object store (see Section 6.1.3) all 233 certificate objects, for which the URI matches the URI extracted 234 from the TAL in the previous step, and the public key matches the 235 subjectPublicKeyInfo extension of the TAL (see Section 2.1 of 236 [RFC7730]). 238 4. If no, or more than one such objects are found, issue an error 239 and abort certificate tree validation process with an error. 240 Otherwise, use the single found object as the Trust Anchor 241 certificate. 243 4.2. CA Certificate Validation 245 The following steps describe the validation of a single CA Resource 246 certificate: 248 1. If both the caRepository (Section 4.8.8.1 of [RFC6487]), and the 249 id-ad-rpkiNotify (Section 3.2 of [I-D.ietf-sidr-delta-protocol]) 250 SIA pointers are present in the CA certificate, use a local 251 policy to determine which pointer to use. Extract the URI from 252 the selected pointer and pass it to the object fetcher (see 253 Section 5.1.1). 255 2. For the CA certificate, find the current manifest and certificate 256 revocation list (CRL), using the procedure described in 257 Section 4.2.1. If no such manifest and CRL could be found, stop 258 validation of this certificate, consider it invalid, and issue an 259 error. 261 3. Compare the URI found in the id-ad-rpkiManifest field 262 (Section 4.8.8.1 of [RFC6487]) of the SIA extension of the 263 certificate with the URI of the manifest found in the previous 264 step. If they are different, issue a warning, but continue 265 validation process using this manifest object. (This warning 266 indicates that there is a mismatch between the expected and the 267 actual location of an object in a repository. See Section 9 for 268 the explanation of this mismatch and the decision taken.) 270 4. Perform manifest entries discovery and validation as described in 271 Section 4.2.2. 273 5. Validate all resource certificate objects found on the manifest, 274 using the CRL object found on the manifest: 276 * if the strict validation option is enabled by the operator, 277 the validation is performed according to Section 7 of 278 [RFC6487], 280 * otherwise, the validation is performed according to Section 7 281 of [RFC6487], with the exception of the resource certification 282 path validation, that is performed according to 283 Section 4.2.4.4 of 284 [I-D.ietf-sidr-rpki-validation-reconsidered]. 286 (Note that this implementation uses the operator configuration to 287 decide which algorithm to use for path validation. It applies 288 selected algorithm to all resource certificates, rather than 289 applying appropriate algorithm per resource certificate, based on 290 the object identifier (OID) for the Certificate Policy found in 291 that certificate, as specified in 292 [I-D.ietf-sidr-rpki-validation-reconsidered].) 294 6. Validate all ROA objects found on the manifest, using the CRL 295 object found on the manifest, according to Section 4 of 296 [RFC6482]. 298 7. Validate all Ghostbusters Record objects found on the manifest, 299 using the CRL object found on the manifest, according to 300 Section 7 of [RFC6493]. 302 8. For every valid CA certificate object found on the manifest, 303 apply the procedure described in this section (Section 4.2), 304 recursively, provided that this CA certificate (identified by its 305 SKI) has not yet been validated during current tree validation 306 run. 308 4.2.1. Finding the most recent valid manifest and CRL 310 1. Fetch from the store (see Section 6.1.4) all objects of type 311 manifest, whose certificate's AKI extension matches the SKI of 312 the current CA certificate. If no such objects are found, stop 313 processing the current CA certificate and issue an error. 315 2. Find among found objects the manifest object with the highest 316 manifestNumber field (Section 4.2.1 of [RFC6486]), for which all 317 following conditions are met: 319 * There is only one entry in the manifest for which the store 320 contains exactly one object of type CRL, the hash of which 321 matches the hash of the entry. 323 * The manifest's certificate AKI equals the above CRL's AKI. 325 * The above CRL is a valid object according to Section 6.3 of 326 [RFC5280]. 328 * The manifest is a valid object according to Section 4.4 of 329 [RFC6486], and its EE certificates is not in the CRL found 330 above. 332 3. If there is an object that matches above criteria, consider this 333 object to be the valid manifest, and the CRL found at the 334 previous step - the valid CRL for the current CA certificate's 335 publication point. 337 4. Report an error for every other manifest with a number higher 338 than the number of the valid manifest. 340 4.2.2. Manifest entries validation 342 For every entry in the manifest object: 344 1. Construct an entry's URI by appending the entry name to the 345 current CA's publication point URI. 347 2. Get all objects from the store whose hash attribute equals 348 entry's hash (see Section 6.1.2). 350 3. If no such objects are found, issue an error for this manifest 351 entry and progress to the next entry. This case indicates that 352 the repository does not have an object at the location listed in 353 the manifest, or that the object's hash does not match the hash 354 listed in the manifest. 356 4. For every found object, compare its URI with the URI of the 357 manifest entry. 359 * For every object with a non-matching URI issue a warning. 360 This case indicates that the object from the manifest entry is 361 (also) found at a different location in a (possibly different) 362 repository. 364 * If no objects with a matching URI are found, issue a warning. 365 This case indicates that there is no object found in the 366 repository at the location listed in the manifest entry (but 367 there is at least one matching object found at a different 368 location). 370 5. Use all found objects for further validation as per Section 4.2. 372 Please note that the above steps will not reject objects whose hash 373 matches the hash listed in the manifest, but the URI does not. See 374 Section 9.2 for additional information. 376 4.3. Object Store Cleanup 378 At the end of every TA tree validation some objects are removed from 379 the store using the following rules: 381 1. Given all objects that were encountered during the current 382 validation run, remove from the store (Section 6.1.6) all objects 383 whose URI attribute matches the URI of one of the encountered 384 objects, but the content's hash is different. This removes from 385 the store objects that were replaced in the repository by their 386 newer versions with the same URIs. 388 2. Remove from the store all objects that were last encountered 389 during validation a long time ago (as specified by the local 390 policy). This removes objects that do not appear on any valid 391 manifest anymore (but possibly are still published in a 392 repository). 394 3. Remove from the store all objects that were downloaded recently 395 (as specified by the local policy), but have never been used in 396 the validation process. This removes objects that have never 397 appeared on any valid manifest. 399 Shortening the time interval used in step 2 will free more disk space 400 used by the store, at the expense of downloading removed objects 401 again if they are still published in the repository. 403 Extending the time interval used in step 3 will prevent repeated 404 downloads of repository objects, with the risk that such objects, if 405 created massively by mistake or by an adversary, will fill up local 406 disk space, if they are not cleaned up promptly. 408 5. Remote Objects Fetcher 410 The fetcher is responsible for downloading objects from remote 411 repositories (described in Section 3 of [RFC6481]) using rsync 412 protocol ([rsync]), or RPKI Repository Delta Protocol (RRDP) 413 ([I-D.ietf-sidr-delta-protocol]). 415 5.1. Fetcher Operations 417 For every visited URI the fetcher keeps track of the last time a 418 successful fetch occurred. 420 5.1.1. Fetch repository objects 422 This operation receives one parameter - a URI. For an rsync 423 repository this URI points to a directory. For an RRDP repository it 424 points to the repository's notification file. 426 The fetcher performs following steps: 428 1. If data associated with the URI has been downloaded recently (as 429 specified by the local policy), skip following steps. 431 2. Download remote objects using the URI provided (for an rsync 432 repository use recursive mode). If the URI contains schema 433 "https" and download has failed, issue a warning, replace "https" 434 schema in the URI by "http", and try to download objects again, 435 using the resulting URI. 437 3. If remote objects can not be downloaded, issue an error and skip 438 following steps. 440 4. Perform syntactic verification of fetched objects. The type of 441 every object (certificate, manifest, CRL, ROA, or Ghostbusters 442 record), is determined based on the object's filename extension 443 (.cer, .mft, .crl, .roa, and .gbr, respectively). The syntax of 444 the object is described in Section 4 of [RFC6487] for resource 445 certificates, step 1 of Section 3 of [RFC6488] for signed 446 objects, and specifically, Section 4 of [RFC6486] for manifests, 447 [RFC5280] for CRLs, Section 3 of [RFC6482] for ROAs, and 448 Section 5 of [RFC6493] for Ghostbusters records. 450 5. Put every downloaded and syntactically correct object in the 451 object store (Section 6.1.1). 453 The time interval used in the step 1 should be chosen based on the 454 acceptable delay in receiving repository updates. 456 5.1.2. Fetch single repository object 458 This operation receives one parameter - a URI that points to an 459 object in a repository. 461 The fetcher performs following operations: 463 1. Download remote object using the URI provided. If the URI 464 contains "https" schema and download failed, issue a warning, 465 replace "https" schema in the URI by "http", and try to download 466 the object using the resulting URI. 468 2. If the remote object can not be downloaded, issue an error and 469 skip following steps. 471 3. Perform syntactic verification of fetched object. The type of 472 object (certificate, manifest, CRL, ROA, or Ghostbusters record), 473 is determined based on the object's filename extension (.cer, 474 .mft, .crl, .roa, and .gbr, respectively). The syntax of the 475 object is described in Section 4 of [RFC6487] for resource 476 certificates, step 1 of Section 3 of [RFC6488] for signed 477 objects, and specifically, Section 4 of [RFC6486] for manifests, 478 [RFC5280] for CRLs, Section 3 of [RFC6482] for ROAs, and 479 Section 5 of [RFC6493] for Ghostbusters records. 481 4. If the downloaded object is not syntactically correct, issue an 482 error and skip further steps. 484 5. Delete all objects from the object store (Section 6.1.5) whose 485 URI matches the URI given. 487 6. Put the downloaded object in the object store (Section 6.1.1). 489 6. Local Object Store 491 6.1. Store Operations 493 6.1.1. Store Repository Object 495 Put given object in the store, along with its type, URI, hash, and 496 AKI, if there is no record with the same hash and URI fields. Note 497 that in the (unlikely) event of hash collision the given object will 498 not replace the object in the store. 500 6.1.2. Get objects by hash 502 Retrieve all objects from the store whose hash attribute matches the 503 given hash. 505 6.1.3. Get certificate objects by URI 507 Retrieve from the store all objects of type certificate, whose URI 508 attribute matches the given URI. 510 6.1.4. Get manifest objects by AKI 512 Retrieve from the store all objects of type manifest, whose AKI 513 attribute matches the given AKI. 515 6.1.5. Delete objects for a URI 517 For a given URI, delete all objects in the store with matching URI 518 attribute. 520 6.1.6. Delete outdated objects 522 For a given URI and a list of hashes, delete all objects in the store 523 with matching URI, whose hash attribute is not in the given list of 524 hashes. 526 6.1.7. Update object's validation time 528 For all objects in the store whose hash attribute matches the given 529 hash, set the last validation time attribute to the given timestamp. 531 7. Acknowledgements 533 This document describes the algorithm as it is implemented by the 534 software development team at the RIPE NCC. The authors would also 535 like to acknowledge contributions by Carlos Martinez, Andy Newton, 536 Rob Austein, and Stephen Kent. 538 8. IANA Considerations 540 This document has no actions for IANA. 542 9. Security Considerations 544 9.1. Hash collisions 546 This implementation will not detect possible hash collisions in the 547 hashes of repository objects (calculated using the file hash 548 algorithm specified in [RFC6485]). It considers objects with same 549 hash values as identical. 551 9.2. Mismatch between the expected and the actual location of an object 552 in the repository 554 According to Section 2 of [RFC6481], all objects issued by a 555 particular CA certificate are expected to be located in one 556 repository publication point, specified in the SIA extension of that 557 CA certificate. The manifest object issued by that CA certificate 558 enumerates all other issued objects, listing their file names and 559 content hashes. 561 However, it is possible that an object whose content hash matches the 562 hash listed in the manifest, has either a different file name, or is 563 located at a different publication point in a repository. 565 On the other hand, all RPKI objects, either explicitly or within 566 their embedded EE certificate, have an Authority Key Identifier 567 extension that contains the key identifier of their issuing CA 568 certificate. Therefore it is always possible to perform an RPKI 569 validation of the object whose expected location does not match its 570 actual location, provided that the certificate that matches the AKI 571 of the object in question is known to the system that performs 572 validation. 574 In case of a mismatch described above this implementation will not 575 exclude an object from further validation merely because it's actual 576 location or file name does not match the expected location or file 577 name. This decision was chosen because the actual location of a file 578 in a repository is taken from the repository retrieval mechanism, 579 which, in case of an rsync repository, does not provide any 580 cryptographic security, and in case of an RRDP repository, provides 581 only a transport layer security, with the fallback to unsecured 582 transport. On the other hand, the manifest is an RPKI signed object, 583 and its content could be verified in the context of the RPKI 584 validation. 586 9.3. Manifest content versus publication point content 588 This algorithm uses the content of a manifest object to determine 589 other objects issued by a CA certificate. It verifies that the 590 manifest is located in the publication point designated in the CA 591 Certificate's SIA extension. However, if there are other (not listed 592 in the manifest) objects located in the same publication point 593 directory, they are ignored, even if they might be valid and issued 594 by the same CA certificate as the manifest. (This behavior is 595 allowed, but not required, by [RFC6486].) 597 9.4. Storing of a TA certificate object before its complete validation 599 When fetching and storing a TA certificate to the object store, only 600 a syntactic validation of a downloaded object is performed before 601 newly downloaded object replaces the previously downloaded object in 602 the object store (see Section 5.1.2). If an attacker will be able to 603 replace a genuine TA certificate by a syntactically valid certificate 604 object (either by manipulating the content of a repository, or by a 605 man-in-the-middle attack), this implementation will discard 606 previously downloaded genuine object, and replace it by a false 607 object. Such false object will be detected later, but the validation 608 of the whole RPKI tree under this TA will be aborted, as described in 609 Section 4. 611 9.5. Possible denial of service 613 The store cleanup procedure described in Section 4.3 tries to 614 minimise removal and subsequent re-fetch of objects that are 615 published in a repository, but not used in the validation. Once such 616 objects are removed from the remote repository, they will be 617 discarded from the local object store after a period of time 618 specified by a local policy. By generating an excessive amount of 619 syntactically valid RPKI objects, a man-in-the-middle attack between 620 a validating tool and a repository could force an implementation to 621 fetch and store those objects in the object store before they are 622 validated and discarded, leading to an out-of-memory or out-of-disk- 623 space conditions, and, subsequently, a denial of service. 625 10. References 627 10.1. Normative References 629 [I-D.ietf-sidr-delta-protocol] 630 Bruijnzeels, T., Muravskiy, O., Weber, B., and R. Austein, 631 "RPKI Repository Delta Protocol (RRDP)", draft-ietf-sidr- 632 delta-protocol-08 (work in progress), March 2017. 634 [I-D.ietf-sidr-rpki-validation-reconsidered] 635 Huston, G., Michaelson, G., Martinez, C., Bruijnzeels, T., 636 Newton, A., and D. Shaw, "RPKI Validation Reconsidered", 637 draft-ietf-sidr-rpki-validation-reconsidered-10 (work in 638 progress), December 2017. 640 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 641 Housley, R., and W. Polk, "Internet X.509 Public Key 642 Infrastructure Certificate and Certificate Revocation List 643 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 644 . 646 [RFC6481] Huston, G., Loomans, R., and G. Michaelson, "A Profile for 647 Resource Certificate Repository Structure", RFC 6481, 648 DOI 10.17487/RFC6481, February 2012, 649 . 651 [RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route 652 Origin Authorizations (ROAs)", RFC 6482, 653 DOI 10.17487/RFC6482, February 2012, 654 . 656 [RFC6485] Huston, G., "The Profile for Algorithms and Key Sizes for 657 Use in the Resource Public Key Infrastructure (RPKI)", 658 RFC 6485, DOI 10.17487/RFC6485, February 2012, 659 . 661 [RFC6486] Austein, R., Huston, G., Kent, S., and M. Lepinski, 662 "Manifests for the Resource Public Key Infrastructure 663 (RPKI)", RFC 6486, DOI 10.17487/RFC6486, February 2012, 664 . 666 [RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for 667 X.509 PKIX Resource Certificates", RFC 6487, 668 DOI 10.17487/RFC6487, February 2012, 669 . 671 [RFC6488] Lepinski, M., Chi, A., and S. Kent, "Signed Object 672 Template for the Resource Public Key Infrastructure 673 (RPKI)", RFC 6488, DOI 10.17487/RFC6488, February 2012, 674 . 676 [RFC6493] Bush, R., "The Resource Public Key Infrastructure (RPKI) 677 Ghostbusters Record", RFC 6493, DOI 10.17487/RFC6493, 678 February 2012, . 680 [RFC7730] Huston, G., Weiler, S., Michaelson, G., and S. Kent, 681 "Resource Public Key Infrastructure (RPKI) Trust Anchor 682 Locator", RFC 7730, DOI 10.17487/RFC7730, January 2016, 683 . 685 10.2. Informative References 687 [github] "RIPE NCC RPKI Validator on GitHub", 688 . 690 [rsync] "Rsync home page", . 692 Authors' Addresses 694 Oleg Muravskiy 695 RIPE NCC 697 Email: oleg@ripe.net 698 URI: https://www.ripe.net/ 699 Tim Bruijnzeels 700 NLNetLabs 702 Email: tim@nlnetlabs.nl 703 URI: https://www.nlnetlabs.nl/