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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Secure Inter-Domain Routing M. Lepinski 2 Working Group S. Kent 3 Internet Draft BBN Technologies 4 Intended status: Informational March 9, 2009 5 Expires: September 9, 2009 7 An Infrastructure to Support Secure Internet Routing 8 draft-ietf-sidr-arch-05.txt 10 Status of this Memo 12 This Internet-Draft is submitted to IETF in full conformance with the 13 provisions of BCP 78 and BCP 79. 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 This Internet-Draft will expire on September 9, 2009. 33 Copyright Notice 35 Copyright (c) 2009 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (http://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. 45 Abstract 46 This document describes an architecture for an infrastructure to 47 support improved security of Internet routing. The foundation of this 48 architecture is a public key infrastructure (PKI) that represents the 49 allocation hierarchy of IP address space and Autonomous System 50 Numbers; and a distributed repository system for storing and 51 disseminating the data objects that comprise the PKI, as well as 52 other signed objects necessary for improved routing security. As an 53 initial application of this architecture, the document describes how 54 a legitimate holder of IP address space can explicitly and verifiably 55 authorize one or more ASes to originate routes to that address space. 56 Such verifiable authorizations could be used, for example, to more 57 securely construct BGP route filters. 59 Table of Contents 61 1. Introduction...................................................3 62 2. PKI for Internet Number Resources..............................5 63 2.1. Role in the overall architecture..........................5 64 2.2. CA Certificates...........................................6 65 2.3. End-Entity (EE) Certificates..............................7 66 2.4. Trust Anchors.............................................8 67 2.5. Default Trust Anchor Considerations.....Error! Bookmark not 68 defined. 69 2.6. Representing Early-Registration Transfers (ERX)...........9 70 3. Route Origination Authorizations..............................10 71 3.1. Role in the overall architecture.........................10 72 3.2. Syntax and semantics.....................................11 73 4. Repositories..................................................12 74 4.1. Role in the overall architecture.........................13 75 4.2. Contents and structure...................................13 76 4.3. Access protocols.........................................15 77 4.4. Access control...........................................15 78 5. Manifests.....................................................16 79 5.1. Syntax and semantics.....................................16 80 6. Local Cache Maintenance.......................................17 81 7. Common Operations.............................................18 82 7.1. Certificate issuance.....................................18 83 7.2. ROA management...........................................19 84 7.2.1. Single-homed subscribers (without portable allocations) 85 ...........................................................20 86 7.2.2. Multi-homed subscribers.............................20 87 7.2.3. Portable allocations................................21 88 7.3. Route filter construction......Error! Bookmark not defined. 89 8. Security Considerations.......................................21 90 9. IANA Considerations...........................................21 91 10. Acknowledgments..............................................21 92 11. References...................................................23 93 11.1. Normative References....................................23 94 11.2. Informative References..................................23 95 Authors' Addresses...............................................24 96 Intellectual Property Statement..................................24 97 Disclaimer of Validity.................Error! Bookmark not defined. 99 1. Introduction 101 This document describes an architecture for an infrastructure to 102 support improved security for BGP routing [2] for the Internet. The 103 architecture encompasses three principle elements: 105 . a public key infrastructure (PKI) 107 . digitally-signed routing objects to support routing security 109 . a distributed repository system to hold the PKI objects and the 110 signed routing objects 112 The architecture described by this document enables an entity to 113 verifiably assert that it is the legitimate holder of a set of IP 114 addresses or a set of Autonomous System (AS) numbers. As an initial 115 application of this architecture, the document describes how a 116 legitimate holder of IP address space can explicitly and verifiably 117 authorize one or more ASes to originate routes to that address space. 118 Such verifiable authorizations could be used, for example, to more 119 securely construct BGP route filters. In addition to this initial 120 application, the infrastructure defined by this architecture also is 121 intended to provide future support for security protocols such as S- 122 BGP [11] or soBGP [12]. This architecture is applicable to the 123 routing of both IPv4 and IPv6 datagrams. IPv4 and IPv6 are currently 124 the only address families supported by this architecture. Thus, for 125 example, use of this architecture with MPLS labels is beyond the 126 scope of this document. 128 In order to facilitate deployment, the architecture takes advantage 129 of existing technologies and practices. The structure of the PKI 130 element of the architecture corresponds to the existing resource 131 allocation structure. Thus management of this PKI is a natural 132 extension of the resource-management functions of the organizations 133 that are already responsible for IP address and AS number resource 134 allocation. Likewise, existing resource allocation and revocation 135 practices have well-defined correspondents in this architecture. Note 136 that while the initial focus of this architecture is routing security 137 applications, the PKI described in this document could be used to 138 support other applications that make use of attestations of IP 139 address or AS number resource holdings. 141 To ease implementation, existing IETF standards are used wherever 142 possible; for example, extensive use is made of the X.509 certificate 143 profile defined by PKIX [3] and the extensions for IP Addresses and 144 AS numbers representation defined in RFC 3779 [5]. Also CMS [4] is 145 used as the syntax for the newly-defined signed objects required by 146 this infrastructure. 148 As noted above, the architecture is comprised of three main 149 components: an X.509 PKI in which certificates attest to holdings of 150 IP address space and AS numbers; non-certificate/CRL signed objects 151 (including route origination authorizations and manifests) used by 152 the infrastructure; and a distributed repository system that makes 153 all of these signed objects available for use by ISPs in making 154 routing decisions. These three basic components enable several 155 security functions; this document describes how they can be used to 156 improve route filter generation, and to perform several other common 157 operations in such a way as to make them cryptographically 158 verifiable. 160 1.1. Terminology 162 It is assumed that the reader is familiar with the terms and concepts 163 described in "Internet X.509 Public Key Infrastructure Certificate 164 and Certificate Revocation List (CRL) Profile" [3], and "X.509 165 Extensions for IP Addresses and AS Identifiers" [5]. 167 Throughout this document we use the terms "address space holder" or 168 "holder of IP address space" interchangeably to refer to a legitimate 169 holder of IP address space who has received this address space 170 through the standard IP address allocation hierarchy. That is, the 171 address space holder has either directly received the address space 172 as an allocation from a Regional Internet Registry (RIR) or IANA; or 173 else the address space holder has received the address space as a 174 sub-allocation from a National Internet Registry (NIR) or Local 175 Internet Registry (LIR). We use the term "resource holder" to refer 176 to a legitimate holder of either IP address or AS number resources. 178 Throughout this document we use the terms "registry" and ISP to refer 179 to an entity that has an IP address space and/or AS number allocation 180 that it is permitted to sub-allocate. We use the term "subscriber" to 181 refer to an entity (e.g., an enterprise) that receives an IP address 182 space and/or AS number allocation, but does not sub-allocate its 183 resources. 185 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 186 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 187 document are to be interpreted as described in RFC-2119 [1]. 189 2. PKI for Internet Number Resources 191 Because the holder of a block IP address space is entitled to define 192 the topological destination of IP datagrams whose destinations fall 193 within that block, decisions about inter-domain routing are 194 inherently based on knowledge of the allocation of the IP address 195 space. Thus, a basic function of this architecture is to provide 196 cryptographically verifiable attestations as to these allocations. In 197 current practice, the allocation of IP addresses is hierarchic. The 198 root of the hierarchy is IANA. Below IANA are five Regional Internet 199 Registries (RIRs), each of which manages address and AS number 200 allocation within a defined geopolitical region. In some regions the 201 third tier of the hierarchy includes National Internet Registries 202 (NIRs) as well as Local Internet Registries (LIRs) and subscribers 203 with so-called "portable" (provider-independent) allocations. (The 204 term LIR is used in some regions to refer to what other regions 205 define as an ISP. Throughout the rest of this document we will use 206 the term LIR/ISP to simplify references to these entities.) In other 207 regions the third tier consists only of LIRs/ISPs and subscribers 208 with portable allocations. 210 In general, the holder of a block of IP address space may sub- 211 allocate portions of that block, either to itself (e.g., to a 212 particular unit of the same organization), or to another 213 organization, subject to contractual constraints established by the 214 registries. Because of this structure, IP address allocations can be 215 described naturally by a hierarchic public-key infrastructure, in 216 which each certificate attests to an allocation of IP addresses, and 217 issuance of subordinate certificates corresponds to sub-allocation of 218 IP addresses. The above reasoning holds true for AS number resources 219 as well, with the difference that, by convention, AS numbers may not 220 be sub-allocated except by RIRs or NIRs. Thus allocations of both IP 221 addresses and AS numbers can be expressed by the same PKI. Such a 222 PKI is a central component of this architecture. 224 2.1. Role in the overall architecture 226 Certificates in this PKI are called Resource Certificates, and 227 conform to the certificate profile for such certificates [6]. 228 Resource certificates attest to the allocation by the (certificate) 229 issuer of IP addresses or AS numbers to the subject. They do this by 230 binding the public key contained in the Resource Certificate to the 231 IP addresses or AS numbers included in the certificate's IP Address 232 Delegation or AS Identifier Delegation Extensions, respectively, as 233 defined in RFC 3779 [5]. 235 An important property of this PKI is that certificates do not attest 236 to the identity of the subject. Therefore, the subject names used in 237 certificates are not intended to be "descriptive." That is, this PKI 238 is intended to provide authorization, but not authentication. This is 239 in contrast to most PKIs where the issuer ensures that the 240 descriptive subject name in a certificate is properly associated with 241 the entity that holds the private key corresponding to the public key 242 in the certificate. Because issuers need not verify the right of an 243 entity to use a subject name in a certificate, they avoid the costs 244 and liabilities of such verification. This makes it easier for these 245 entities to take on the additional role of Certificate Authority 246 (CA). 248 Most of the certificates in the PKI assert the basic facts on which 249 the rest of the infrastructure operates. CA certificates within the 250 PKI attest to IP address space and AS number holdings. End-entity 251 (EE) certificates are issued by resource holder CAs to delegate the 252 authority attested by their allocation certificates. The primary use 253 for EE certificates is the validation of Route Origination 254 Authorizations (ROAs). Additionally, signed objects called manifests 255 will be used to help ensure the integrity of the repository system, 256 and the signature on each manifest will be verified via an EE 257 certificate. 259 2.2. CA Certificates 261 Any resource holder who is authorized to sub-allocate these resources 262 must be able to issue Resource Certificates to correspond to these 263 sub-allocations. Thus, for example, CA certificates will be 264 associated with IANA and each of the RIRs, NIRs, and LIRs/ISPs. A CA 265 certificate also is required to enable a resource holder to issue 266 ROAs, because it must issue the corresponding end-entity certificate 267 used to validate each ROA. Thus some entities that do not sub- 268 allocate their resources also will need to have CA certificates for 269 their allocations, e.g., a multi-homed subscriber with a portable 270 allocation, to enable them to issue ROAs. (A subscriber who is not 271 multi-homed, whose allocation comes from an LIR/ISP, and who has not 272 moved to a different LIR/ISP, need not be represented in the PKI. 273 Moreover, a multi-homed subscriber with an allocation from an LIR/ISP 274 may or may not need to be explicitly represented, as discussed in 275 Section 7.2.2) 277 Unlike in most PKIs, the distinguished name of the subject in a CA 278 certificate is chosen by the certificate issuer. If the subject of a 279 certificate is an RIR or IANA, then the distinguished name of the 280 subject will be chosen to convey the identity of the registry and 281 should consist of (a subset of) the following attributes: country, 282 organization, organizational unit, and common name. For example, an 283 appropriate subject name for the APNIC RIR might be: 285 . Country: AU 287 . Organization: Asia Pacific Network Information Centre 289 . Common Name: APNIC Resource Certification Authority 291 If the subject of a certificate is not an RIR or IANA, (e.g., 292 the subject is a NIR, or LIR/ISP) the distinguished name must not 293 attempt to convey the identity of the subject in a descriptive 294 fashion. The subject's distinguished name must be unique among all 295 certificates issued by a given authority. In this PKI, the 296 certificate issuer, being an RIR, NIR, or LIR/ISP, is not in the 297 business of verifying the legal right of the subject to assert a 298 particular identity. Therefore, selecting a distinguished name that 299 does not convey the identity of the subject in a descriptive fashion 300 minimizes the opportunity for the subject to misuse the certificate 301 to assert an identity, and thus minimizes the legal liability of the 302 issuer. Since all CA certificates are issued to subjects with whom 303 the issuer has an existing relationship, it is recommended that the 304 issuer select a subject name that enables the issuer to easily link 305 the certificate to existing database records associated with the 306 subject. For example, an authority may use internal database keys or 307 subscriber IDs as the subject common name in issued certificates. 309 Each Resource Certificate attests to an allocation of resources to a 310 resource holder, so entities that have allocations from multiple 311 sources will have multiple CA certificates. A CA also may issue 312 distinct certificates for each distinct allocation to the same 313 entity, if the CA and the resource holder agree that such an 314 arrangement will facilitate management and use of the certificates. 315 For example, an LIR/ISP may have several certificates issued to it by 316 one registry, each describing a distinct set of address blocks, 317 because the LIR/ISP desires to treat the allocations as separate. 319 2.3. End-Entity (EE) Certificates 321 The private key corresponding to public key contained in an EE 322 certificate is not used to sign other certificates in a PKI. The 323 primary function of end-entity certificates in this PKI is the 324 verification of signed objects that relate to the usage of the 325 resources described in the certificate, e.g., ROAs and manifests. 327 For ROAs and manifests there will be a one-to-one correspondence 328 between end-entity certificates and signed objects, i.e., the private 329 key corresponding to each end-entity certificate is used to sign 330 exactly one object, and each object is signed with only one key. 331 This property allows the PKI to be used to revoke these signed 332 objects, rather than creating a new revocation mechanism. When the 333 end-entity certificate used to sign an object has been revoked, the 334 signature on that object (and any corresponding assertions) will be 335 considered invalid, so a signed object can be effectively revoked by 336 revoking the end-entity certificate used to sign it. 338 A secondary advantage to this one-to-one correspondence is that the 339 private key corresponding to the public key in a certificate is used 340 exactly once in its lifetime, and thus can be destroyed after it has 341 been used to sign its one object. This fact should simplify key 342 management, since there is no requirement to protect these private 343 keys for an extended period of time. 345 Although this document describes only two uses for end-entity 346 certificates, additional uses will likely be defined in the future. 347 For example, end-entity certificates could be used as a more general 348 authorization for their subjects to act on behalf of the specified 349 resource holder. This could facilitate authentication of inter-ISP 350 interactions, or authentication of interactions with the repository 351 system. These additional uses for end-entity certificates may 352 require retention of the corresponding private keys, even though this 353 is not required for the private keys associated with end-entity 354 certificates keys used for verification of ROAs and manifests, as 355 described above. 357 2.4. Trust Anchors 359 In any PKI, each relying party (RP) chooses its own set of trust 360 anchors. This general property of PKIs applies here as well. There is 361 an extant IP address space and AS number allocation hierarchy, and 362 thus IANA and/or the five RIRs are obvious candidates to be default 363 TAs here. Nonetheless, each RP ultimately chooses the set of trust 364 anchors it will use for certificate validation. 366 For example, a RP (e.g., an LIR/ISP) could create a trust anchor to 367 which all address space and/or all AS numbers are assigned, and for 368 which the RP knows the corresponding private key. The RP could then 369 issue certificates under this trust anchor to whatever entities in 370 the PKI it wishes, with the result that the certification paths 371 terminating at this locally-installed trust anchor will satisfy the 372 RFC 3779 validation requirements. A large ISP that uses private 373 (i.e., RFC 1918) IP address space and runs BGP internally will need 374 to create this sort of trust anchor to accommodate a CA to which all 375 private (RFC 1918) address space is assigned. The RP could then issue 376 certificates under this CA that correspond to the RP's internal use 377 of private address space. 379 Note that a RP who elects to create and manage its own set of trust 380 anchors may fail to detect allocation errors that arise under such 381 circumstances, but the resulting vulnerability is local to the RP. 383 It is expected that some parties within the extant IP address space 384 and AS number allocation hierarchy may wish to publish trust anchor 385 material for possible use by relying parties. A standard profile for 386 the publication of trust anchor material for this public key 387 infrastructure can be found in [9]. 389 2.5. Representing Early-Registration Transfers (ERX) 391 Currently, IANA allocates IPv4 address space to the RIRs at the level 392 of /8 prefixes. However, there exist allocations that cross these RIR 393 boundaries. For example, A LACNIC customer may have an allocation 394 that falls within a /8 prefix administered by ARIN. Therefore, the 395 resource PKI must be able to represent such transfers from one RIR to 396 another in a manner that permits the validation of certificates with 397 RFC 3779 extensions. 399 +-------------------------------+ 400 | | 401 | LACNIC Administrative | 402 | Boundary | 403 | | 404 +--------+ | +--------+ | +--------+ 405 | ARIN | | | LACNIC | | | RIPE | 406 | ROOT | | | ROOT | | | ROOT | 407 +--------+ | +--------+ | +--------+ 408 \ | | / 409 ------------ ------------ 410 | \ / | 411 | +--------+ +--------+ | 412 | | LACNIC | | LACNIC | | 413 | | CA | | CA | | 414 | +--------+ +--------+ | 415 | | 416 +-------------------------------+ 418 FIGURE 1: Representing EXR 420 To represent such transfers, RIRs will need to manage multiple CA 421 certificates, each with distinct public (and corresponding private) 422 keys. Each RIR will have a single "root" certificate (e.g., a self- 423 signed certificate or a certificate signed by IANA, see Section 2.5), 424 plus one additional CA certificate for each RIR from which it 425 receives a transfer. Each of these additional CA certificates will be 426 issued under the "root" certificate of the RIR from which the 427 transfer is received. This means that although the certificate is 428 bound to the RIR that receives the transfer, for the purposes of 429 certificate path construction and validation, it does not appear 430 under that RIR's "root" certificate (see Figure 1). 432 3. Route Origination Authorizations 434 The information on IP address allocation provided by the PKI is not, 435 in itself, sufficient to guide routing decisions. In particular, BGP 436 is based on the assumption that the AS that originates routes for a 437 particular prefix is authorized to do so by the holder of that prefix 438 (or an address block encompassing the prefix); the PKI contains no 439 information about these authorizations. A Route Origination 440 Authorization (ROA) makes such authorization explicit, allowing a 441 holder of IP address space to create an object that explicitly and 442 verifiably asserts that an AS is authorized originate routes to a 443 given set of prefixes. 445 3.1. Role in the overall architecture 447 A ROA is an attestation that the holder of a set of prefixes has 448 authorized an autonomous system to originate routes for those 449 prefixes. A ROA is structured according to the format described in 450 [7]. The validity of this authorization depends on the signer of the 451 ROA being the holder of the prefix(es) in the ROA; this fact is 452 asserted by an end-entity certificate from the PKI, whose 453 corresponding private key is used to sign the ROA. 455 ROAs may be used by relying parties to verify that the AS that 456 originates a route for a given IP address prefix is authorized by the 457 holder of that prefix to originate such a route. For example, an ISP 458 might use validated ROAs as inputs to route filter construction for 459 use by its BGP routers. (See [14] for information on the use of ROAs 460 to validate the origination of BGP routes.) 462 Initially, the repository system will be the primary mechanism for 463 disseminating ROAs, since these repositories will hold the 464 certificates and CRLs needed to verify ROAs. In addition, ROAs also 465 could be distributed in BGP UPDATE messages or via other 466 communication paths, if needed to meet timeliness requirements. 468 3.2. Syntax and semantics 470 A ROA constitutes an explicit authorization for a single AS to 471 originate routes to one or more prefixes, and is signed by the holder 472 of those prefixes. A detailed specification of the ROA syntax can be 473 found in [7] but, at a high level, a ROA consists of (1) an AS 474 number; (2) a list of IP address prefixes; and, optionally, (3) for 475 each prefix, the maximum length of more specific (longer) prefixes 476 that the AS is also authorized to advertise. (This last element 477 facilitates a compact authorization to advertise, for example, any 478 prefixes of length 20 to 24 contained within a given length 20 479 prefix.) 481 Note that a ROA contains only a single AS number. Thus, if an ISP has 482 multiple AS numbers that will be authorized to originate routes to 483 the prefix(es) in the ROA, an address space holder will need to issue 484 multiple ROAs to authorize the ISP to originate routes from any of 485 these ASes. 487 A ROA is signed using the private key corresponding to the public key 488 in an end-entity certificate in the PKI. In order for a ROA to be 489 valid, its corresponding end-entity (EE) certificate must be valid 490 and the IP address prefixes of the ROA must exactly match the IP 491 address prefix(es) specified in the EE certificate's RFC 3779 492 extension. Therefore, the validity interval of the ROA is implicitly 493 the validity interval of its corresponding certificate. A ROA is 494 revoked by revoking the corresponding EE certificate. There is no 495 independent method of invoking a ROA. One might worry that this 496 revocation model could lead to long CRLs for the CA certification 497 that is signing the EE certificates. However, routing announcements 498 on the public internet are generally quite long lived. Therefore, as 499 long as the EE certificates used to verify a ROA are given a validity 500 interval of several months, the likelihood that many ROAs would need 501 to revoked within that time is quite low. 503 --------- --------- 504 | RIR | | NIR | 505 | CA | | CA | 506 --------- --------- 507 | | 508 | | 509 | | 510 --------- --------- 511 | ISP | | ISP | 512 | CA 1 | | CA 2 | 513 --------- --------- 514 | \ | 515 | ----- | 516 | \ | 517 ---------- ---------- ---------- 518 | ISP | | ISP | | ISP | 519 | EE 1a | | EE 1b | | EE 2 | 520 ---------- ---------- ---------- 521 | | | 522 | | | 523 | | | 524 ---------- ---------- ---------- 525 | ROA 1a | | ROA 1b | | ROA 2 | 526 ---------- ---------- ---------- 528 FIGURE 2: This figure illustrates an ISP with allocations from two 529 sources (and RIR and an NIR). It needs two CA certificates due to RFC 530 3779 rules. 532 Because each ROA is associated with a single end-entity certificate, 533 the set of IP prefixes contained in a ROA must be drawn from an 534 allocation by a single source, i.e., a ROA cannot combine allocations 535 from multiple sources. Address space holders who have allocations 536 from multiple sources, and who wish to authorize an AS to originate 537 routes for these allocations, must issue multiple ROAs to the AS. 539 4. Repositories 541 Initially, an LIR/ISP will make use of the resource PKI by acquiring 542 and validating every ROA, to create a table of the prefixes for which 543 each AS is authorized to originate routes. To validate all ROAs, an 544 LIR/ISP needs to acquire all the certificates and CRLs. The primary 545 function of the distributed repository system described here is to 546 store these signed objects and to make them available for download by 547 LIRs/ISPs. Note that this repository system provides a mechanism by 548 which relying parties can pull fresh data at whatever frequency they 549 deem appropriate. However, it does not provide a mechanism for 550 pushing fresh data to relying parties (e.g. by including resource PKI 551 objects in BGP or other protocol messages) and such a mechanism is 552 beyond the scope of the current document. 554 The digital signatures on all objects in the repository ensure that 555 unauthorized modification of valid objects is detectable by relying 556 parties. Additionally, the repository system uses manifests (see 557 Section 5) to ensure that relying parties can detect the deletion of 558 valid objects and the insertion of out of date, valid signed objects. 560 The repository system is also a point of enforcement for access 561 controls for the signed objects stored in it, e.g., ensuring that 562 records related to an allocation of resources can be manipulated only 563 by authorized parties. The use of access controls prevents denial of 564 service attacks based on deletion of or tampering to repository 565 objects. Indeed, although relying parties can detect tampering with 566 objects in the repository, it is preferable that the repository 567 system prevent such unauthorized modifications to the greatest extent 568 possible. 570 4.1. Role in the overall architecture 572 The repository system is the central clearing-house for all signed 573 objects that must be globally accessible to relying parties. When 574 certificates and CRLs are created, they are uploaded to this 575 repository, and then downloaded for use by relying parties (primarily 576 LIRs/ISPs). ROAs and manifests are additional examples of such 577 objects, but other types of signed objects may be added to this 578 architecture in the future. This document briefly describes the way 579 signed objects (certificates, CRLs, ROAs and manifests) are managed 580 in the repository system. As other types of signed objects are added 581 to the repository system it will be necessary to modify the 582 description, but it is anticipated that most of the design principles 583 will still apply. The repository system is described in detail in 584 [10]. 586 4.2. Contents and structure 588 Although there is a single repository system that is accessed by 589 relying parties, it is comprised of multiple databases. These 590 databases will be distributed among registries (RIRs, NIRs, 591 LIRs/ISPs). At a minimum, the database operated by each registry will 592 contain all CA and EE certificates, CRLs, and manifests signed by the 593 CA(s) associated with that registry. Repositories operated by 594 LIRs/ISPs also will contain ROAs. Registries are encouraged to 595 maintain copies of repository data from their customers, and their 596 customer's customers (etc.), to facilitate retrieval of the whole 597 repository contents by relying parties. Ideally, each RIR will hold 598 PKI data from all entities within its geopolitical scope. 600 For every certificate in the PKI, there will be a corresponding file 601 system directory in the repository that is the authoritative 602 publication point for all objects (certificates, CRLs, ROAs and 603 manifests) verifiable via this certificate. A certificate's Subject 604 Information Authority (SIA) extension provides a URI that references 605 this directory. Additionally, a certificate's Authority Information 606 Authority (AIA) extension contains a URI that references the 607 authoritative location for the CA certificate under which the given 608 certificate was issued. That is, if certificate A is used to verify 609 certificate B, then the AIA extension of certificate B points to 610 certificate A, and the SIA extension of certificate A points to a 611 directory containing certificate B (see Figure 2). 613 +--------+ 614 +--------->| Cert A |<----+ 615 | | CRLDP | | +---------+ 616 | | AIA | | +-->| A's CRL |<-+ 617 | +--------- SIA | | | +---------+ | 618 | | +--------+ | | | 619 | | | | | 620 | | +---+----+ | 621 | | | | | 622 | | +---------------|---|-----------------+ | 623 | | | | | | | 624 | +->| +--------+ | | +--------+ | | 625 | | | Cert B | | | | Cert C | | | 626 | | | CRLDP ----+ | | CRLDP -+--------+ 627 +----------- AIA | +----- AIA | | 628 | | SIA | | SIA | | 629 | +--------+ +--------+ | 630 | | 631 +-------------------------------------+ 633 FIGURE 3: In this example, certificates B and C are issued under 634 certificate A. Therefore, the AIA extensions of certificates B and C 635 point to A, and the SIA extension of certificate A points to the 636 directory containing certificates B and C. 638 If a CA certificate is reissued with the same public key, it should 639 not be necessary to reissue (with an updated AIA URI) all 640 certificates signed by the certificate being reissued. Therefore, a 641 certification authority SHOULD use a persistent URI naming scheme for 642 issued certificates. That is, reissued certificates should use the 643 same publication point as previously issued certificates having the 644 same subject and public key, and should overwrite such certificates. 646 4.3. Access protocols 648 Repository operators will choose one or more access protocols that 649 relying parties can use to access the repository system. These 650 protocols will be used by numerous participants in the infrastructure 651 (e.g., all registries, ISPs, and multi-homed subscribers) to maintain 652 their respective portions of it. In order to support these 653 activities, certain basic functionality is required of the suite of 654 access protocols, as described below. No single access protocol need 655 implement all of these functions (although this may be the case), but 656 each function must be implemented by at least one access protocol. 658 Download: Access protocols MUST support the bulk download of 659 repository contents and subsequent download of changes to the 660 downloaded contents, since this will be the most common way in which 661 relying parties interact with the repository system. Other types of 662 download interactions (e.g., download of a single object) MAY also be 663 supported. 665 Upload/change/delete: Access protocols MUST also support mechanisms 666 for the issuers of certificates, CRLs, and other signed objects to 667 add them to the repository, and to remove them. Mechanisms for 668 modifying objects in the repository MAY also be provided. All access 669 protocols that allow modification to the repository (through 670 addition, deletion, or modification of its contents) MUST support 671 verification of the authorization of the entity performing the 672 modification, so that appropriate access controls can be applied (see 673 Section 4.4). 675 Current efforts to implement a repository system use RSYNC [13] as 676 the single access protocol. RSYNC, as used in this implementation, 677 provides all of the above functionality. A document specifying the 678 conventions for use of RSYNC in the PKI will be prepared. 680 4.4. Access control 682 In order to maintain the integrity of information in the repository, 683 controls must be put in place to prevent addition, deletion, or 684 modification of objects in the repository by unauthorized parties. 685 The identities of parties attempting to make such changes can be 686 authenticated through the relevant access protocols. Although 687 specific access control policies are subject to the local control of 688 repository operators, it is recommended that repositories allow only 689 the issuers of signed objects to add, delete, or modify them. 691 Alternatively, it may be advantageous in the future to define a 692 formal delegation mechanism to allow resource holders to authorize 693 other parties to act on their behalf, as suggested in Section 2.3 694 above. 696 5. Manifests 698 A manifest is a signed object listing of all of the signed objects 699 issued by an authority responsible for a publication in the 700 repository system. For each certificate, CRL, or ROA issued by the 701 authority, the manifest contains both the name of the file containing 702 the object, and a hash of the file content. 704 As with ROAs, a manifest is signed by a private key, for which the 705 corresponding public key appears in an end-entity certificate. This 706 EE certificate, in turn, is signed by the CA in question. The EE 707 certificate private key may be used to issue one for more manifests. 708 If the private key is used to sign only a single manifest, then the 709 manifest can be revoked by revoking the EE certificate. In such a 710 case, to avoid needless CRL growth, the EE certificate used to 711 validate a manifest SHOULD expire at the same time that the manifest 712 expires. If an EE certificate is used to issue multiple (sequential) 713 manifests for the CA in question, then there is no revocation 714 mechanism for these individual manifests. 716 Manifests may be used by relying parties when constructing a local 717 cache (see Section 6) to mitigate the risk of an attacker who deletes 718 files from a repository or replaces current signed objects with stale 719 versions of the same object. Such protection is needed because 720 although all objects in the repository system are signed, the 721 repository system itself is untrusted. 723 5.1. Syntax and semantics 725 A manifest constitutes a list of (the hashes of) all the files in a 726 repository point at a particular point in time. A detailed 727 specification of manifest syntax is provided in [8] but, at a high 728 level, a manifest consists of (1) a manifest number; (2) the time the 729 manifest was issued; (3) the time of the next planned update; and (4) 730 a list of filename and hash value pairs. 732 The manifest number is a sequence number that is incremented each 733 time a manifest is issued by the authority. An authority is required 734 to issue a new manifest any time it alters any of its items in the 735 repository, or when the specified time of the next update is reached. 736 A manifest is thus valid until the specified time of the next update 737 or until a manifest is issued with a greater manifest number, 738 whichever comes first. (Note that when an EE certificate is used to 739 sign only a single manifest, whenever the authority issues the new 740 manifest, the CA MUST also issue a new CRL which includes the EE 741 certificate corresponding to the old manifest. The revoked EE 742 certificate for the old manifest will be removed from the CRL when it 743 expires, thus this procedure ought not to result in significant CRLs 744 growth.) 746 6. Local Cache Maintenance 748 In order to utilize signed objects issued under this PKI, a relying 749 party must first obtain a local copy of the valid EE certificates for 750 the PKI. To do so, the relying party performs the following steps: 752 1. Query the registry system to obtain a copy of all certificates, 753 manifests and CRLs issued under the PKI. 755 2. For each CA certificate in the PKI, verify the signature on the 756 corresponding manifest. Additionally, verify that the current 757 time is earlier than the time indicated in the nextUpdate field 758 of the manifest. 760 3. For each manifest, verify that certificates and CRLs issued 761 under the corresponding CA certificate match the hash values 762 contained in the manifest. Additionally, verify that no 763 certificate or manifest listed on the manifest is missing from 764 the repository. If the hash values do not match, or if any 765 certificate or CRL is missing, notify the appropriate repository 766 administrator that the repository data has been corrupted. 768 4. Validate each EE certificate by constructing and verifying a 769 certification path for the certificate (including checking 770 relevant CRLs) to the locally configured set of TAs. (See [6] 771 for more details.) 773 Note that when a relying party performs these operations regularly, 774 it is more efficient for the relying party to request from the 775 repository system only those objects that have changed since the 776 relying party last updated its local cache. A relying party may 777 choose any frequency it desires for downloading and validating 778 updates from the repository. However, a typical ISP might reasonably 779 choose to perform these operations on a daily schedule. Note also 780 that by checking all issued objects against the appropriate manifest, 781 the relying party can be certain that it is not missing an updated 782 version of any object. 784 7. Common Operations 786 Creating and maintaining the infrastructure described above will 787 entail additional operations as "side effects" of normal resource 788 allocation and routing authorization procedures. For example, a 789 subscriber with "portable" address space who enters a relationship 790 with an ISP will need to issue one or more ROAs identifying that ISP, 791 in addition to conducting any other necessary technical or business 792 procedures. The current primary use of this infrastructure is for 793 route filter construction; using ROAs, route filters can be 794 constructed in an automated fashion with high assurance that the 795 holder of the advertised prefix has authorized the origin AS to 796 originate an advertised route. 798 7.1. Certificate issuance 800 There are several operational scenarios that require certificates to 801 be issued. Any allocation that may be sub-allocated requires a CA 802 certificate, e.g., so that certificates can be issued as necessary 803 for the sub-allocations. Holders of "portable" IP address space 804 allocations also must have certificates, so that a ROA can be issued 805 to each ISP that is authorized to originate a route to the allocation 806 (since the allocation does not come from any ISP). Additionally, 807 multi-homed subscribers may require certificates for their 808 allocations if they intend to issue the ROAs for their allocations 809 (see Section 7.2.2). Other resource holders need not be issued CA 810 certificates within the PKI. 812 In the long run, a resource holder will not request resource 813 certificates, but rather receive a certificate as a side effect of 814 the allocation process for the resource. However, initial deployment 815 of the RPKI will entail issuance of certificates to existing resource 816 holders as an explicit event. Note that in all cases, the authority 817 issuing a CA certificate will be the entity who allocates resources 818 to the subject. This differs from most PKIs in which a subject can 819 request a certificate from any certification authority. 821 If a resource holder receives multiple allocations over time, it may 822 accrue a collection of resource certificates to attest to them. If a 823 resource holder receives multiple allocations from the same source, 824 the set of resource certificates may be combined into a single 825 resource certificate, if both the issuer and the resource holder 826 agree. This is accomplished by consolidating the IP Address 827 Delegation and AS Identifier Delegation Extensions into a single 828 extension (of each type) in a new certificate. However, if the 829 certificates for these allocations contain different validity 830 intervals, creating a certificate that combines them might create 831 problems, and thus is NOT RECOMMENDED. 833 If a resource holder's allocations come from different sources, they 834 will be signed by different CAs, and cannot be combined. When a set 835 of resources is no longer allocated to a resource holder, any 836 certificates attesting to such an allocation MUST be revoked. A 837 resource holder SHOULD NOT use the same public key in multiple CA 838 certificates that are issued by the same or differing authorities, as 839 reuse of a key pair complicates path construction. Note that since 840 the subject's distinguished name is chosen by the issuer, a subject 841 who receives allocations from two sources generally will receive 842 certificates with different subject names. 844 7.2. ROA management 846 Whenever a holder of IP address space wants to authorize an AS to 847 originate routes for a prefix within his holdings, he MUST issue an 848 end-entity certificate containing that prefix in an IP Address 849 Delegation extension. He then uses the corresponding private key to 850 sign a ROA containing the designated prefix and the AS number for the 851 AS. The resource holder MAY include more than one prefix in the EE 852 certificate and corresponding ROA if desired. As a prerequisite, 853 then, any address space holder that issues ROAs for a prefix must 854 have a resource certificate for an allocation containing that prefix. 855 The standard procedure for issuing a ROA is as follows: 857 1. Create an end-entity certificate containing the prefix(es) to be 858 authorized in the ROA. 860 2. Construct the payload of the ROA, including the prefixes in the 861 end-entity certificate and the AS number to be authorized. 863 3. Sign the ROA using the private key corresponding to the end- 864 entity certificate (the ROA is comprised of the payload 865 encapsulated in a CMS signed message [7]). 867 4. Upload the end-entity certificate and the ROA to the repository 868 system. 870 The standard procedure for revoking a ROA is to revoke the 871 corresponding end-entity certificate by creating an appropriate CRL 872 and uploading it to the repository system. The revoked ROA and end- 873 entity certificate SHOULD BE removed from the repository system. 875 7.2.1. Single-homed subscribers (without portable allocations) 877 In BGP, a single-homed subscriber with a non-portable allocation does 878 not need to explicitly authorize routes to be originated for the 879 prefix(es) it is using, since its ISP will already advertise a more 880 general prefix and route traffic for the subscriber's prefix as an 881 internal function. Since no routes are originated specifically for 882 prefixes held by these subscribers, no ROAs need to be issued under 883 their allocations; rather, the subscriber's ISP will issue any 884 necessary ROAs for its more general prefixes under resource 885 certificates from its own allocation. Thus, a single-homed subscriber 886 with a non-portable allocation is not included in the RPKI, i.e., it 887 does not receive a CA certificate, nor issue EE certificates or ROAs. 889 7.2.2. Multi-homed subscribers (without portable allocations) 891 Here we consider a subscriber who receives IP address space from a 892 primary ISP (i.e., the IP addresses used by the subscriber are a 893 subset of ISP A's IP address space allocation) and receives redundant 894 upstream connectivity from the primary ISP, as well as one or more 895 secondary ISPs. The preferred option for such a multi-homed 896 subscribers is for the subscriber to obtain an AS number (from an RIR 897 or NIR) and run BGP with each of its upstream providers. In such a 898 case, there are two ways for ROA management to be handled. The first 899 is that the primary ISP issues a CA certificate to the subscriber, 900 and the subscriber issues a ROA to containing the subscriber's AS 901 number and the subscriber's IP address prefixes. The second 902 possibility is that the primary ISP does not issue a ROA to the 903 subscriber, and instead issues a ROA on the subscriber's behalf that 904 contains the subscriber's AS number and the subscriber's IP address 905 prefixes. 907 If the subscriber is unable or unwilling to obtain an AS number and 908 run BGP, the other option is that the multi-homed subscriber can 909 request that the primary ISP create a ROA for each secondary ISP that 910 authorizes the secondary ISP to originate routes to the subscriber's 911 prefixes. The primary ISP will also create a ROA containing its own 912 AS number and the subscriber's prefixes, as it is likely in such a 913 case that the primary ISP wishes to advertise precisely the 914 subscriber's prefixes and not an encompassing aggregate. Note that 915 this approach results in inconsistent origin AS numbers for the 916 subscribers prefixes which are considered undesirable on the public 917 Internet; thus this approach is NOT RECOMMENDED. 919 7.2.3. Portable allocations 921 A resource holder is said to have a portable (provider independent) 922 allocation if the resource holder received its allocation from a RIR 923 or NIR. Because the prefixes represented in such allocations are not 924 taken from an allocation held by an ISP, there is no ISP that holds 925 and advertises a more general prefix. A holder of a portable IP 926 address space allocation MUST authorize one or more ASes to originate 927 routes to these prefixes. Thus the resource holder MUST generate one 928 or more EE certificates and associated ROAs to enable the AS(es) to 929 originate routes for the prefix(es) in question. This ROA is required 930 because none of the ISP's existing ROAs authorize it to originate 931 routes to that portable allocation. 933 8. Security Considerations 935 The focus of this document is security; hence security considerations 936 permeate this specification. 938 The security mechanisms provided by and enabled by this architecture 939 depend on the integrity and availability of the infrastructure it 940 describes. The integrity of objects within the infrastructure is 941 ensured by appropriate controls on the repository system, as 942 described in Section 4.4. Likewise, because the repository system is 943 structured as a distributed database, it should be inherently 944 resistant to denial of service attacks; nonetheless, appropriate 945 precautions should also be taken, both through replication and backup 946 of the constituent databases and through the physical security of 947 database servers. 949 9. IANA Considerations 951 This document requests that the IANA issue RPKI Certificates for the 952 resources for which it is authoritative, i.e., reserved IPv4 953 addresses, IPv6 ULAs, and address space not yet allocated by IANA to 954 the RIRs. IANA SHOULD make available trust anchor material in the 955 format defined in [10] in support of these functions. 957 10. Acknowledgments 959 The architecture described in this draft is derived from the 960 collective ideas and work of a large group of individuals. This work 961 would not have been possible without the intellectual contributions 962 of George Michaelson, Robert Loomans, Sanjaya and Geoff Huston of 963 APNIC, Robert Kisteleki and Henk Uijterwaal of the RIPE NCC, Tim 964 Christensen and Cathy Murphy of ARIN, Rob Austein of ISC and Randy 965 Bush of IIJ. 967 Although we are indebted to everyone who has contributed to this 968 architecture, we would like to especially thank Rob Austein for the 969 concept of a manifest, Geoff Huston for the concept of managing 970 object validity through single-use EE certificate key pairs, and 971 Richard Barnes for help in preparing an early version of this 972 document. 974 11. References 976 11.1. Normative References 978 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 979 Levels", BCP 14, RFC 2119, March 1997. 981 [2] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 982 (BGP-4)", RFC 4271, January 2006 984 [3] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, 985 R., and W. Polk, "Internet X.509 Public Key Infrastructure 986 Certificate and Certificate Revocation List (CRL) Profile", RFC 987 5280, May 2008. 989 [4] Housley, R., "Cryptographic Message Syntax", RFC 3852, July 990 2004. 992 [5] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP 993 Addresses and AS Identifiers", RFC 3779, June 2004. 995 [6] Huston, G., Michaelson, G., and Loomans, R., "A Profile for 996 X.509 PKIX Resource Certificates", draft-ietf-sidr-res-certs- 997 16, February 2009. 999 [7] Lepinski, M., Kent, S., and Kong, D., "A Profile for Route 1000 Origin Authorizations (ROA)", draft-ietf-sidr-roa-format-04, 1001 November 2008. 1003 [8] Austein, R., et al., "Manifests for the Resource Public Key 1004 Infrastructure", draft-ietf-sidr-rpki-manifests-04, October 1005 2008. 1007 [9] Michaelson, G., Kent, S., and Huston, G., "A Profile for Trust 1008 Anchor Material for the Resource Certificate PKI", draft-ietf- 1009 sidr-ta-00, February 2009. 1011 11.2. Informative References 1013 [10] Huston, G., Michaelson, G., and Loomans, R., "A Profile for 1014 Resource Certificate Repository Structure", draft-ietf-sidr- 1015 repos-struct-01, October 2008. 1017 [11] Kent, S., Lynn, C., and Seo, K., "Secure Border Gateway 1018 Protocol (Secure-BGP)", IEEE Journal on Selected Areas in 1019 Communications Vol. 18, No. 4, April 2000. 1021 [12] White, R., "soBGP", May 2005, 1024 [13] Tridgell, A., "rsync", April 2006, 1025 1027 [14] Huston, G., Michaelson, G., "Validation of Route Origination in 1028 BGP using the Resource Certificate PKI", draft-ietf-sidr-roa- 1029 validation-01, October 2008. 1031 Authors' Addresses 1033 Matt Lepinski 1034 BBN Technologies 1035 10 Moulton St. 1036 Cambridge, MA 02138 1038 Email: mlepinski@bbn.com 1040 Stephen Kent 1041 BBN Technologies 1042 10 Moulton St. 1043 Cambridge, MA 02138 1045 Email: kent@bbn.com 1047 Pre-5378 Material Disclaimer 1049 This document may contain material from IETF Documents or IETF 1050 Contributions published or made publicly available before November 1051 10, 2008. The person(s) controlling the copyright in some of this 1052 material may not have granted the IETF Trust the right to allow 1053 modifications of such material outside the IETF Standards Process. 1054 Without obtaining an adequate license from the person(s) controlling 1055 the copyright in such materials, this document may not be modified 1056 outside the IETF Standards Process, and derivative works of it may 1057 not be created outside the IETF Standards Process, except to format 1058 it for publication as an RFC or to translate it into languages other 1059 than English.