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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 July 29, 2009 5 Expires: January 29, 2010 7 An Infrastructure to Support Secure Internet Routing 8 draft-ietf-sidr-arch-08.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 January 29, 20010. 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 in effect on the date of 40 publication of this document (http://trustee.ietf.org/license-info). 41 Please review these documents carefully, as they describe your rights 42 and restrictions with respect to this document. 44 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 1.1. Terminology...............................................4 63 2. PKI for Internet Number Resources..............................5 64 2.1. Role in the overall architecture..........................5 65 2.2. CA Certificates...........................................6 66 2.3. End-Entity (EE) Certificates..............................7 67 2.4. Trust Anchors.............................................8 68 3. Route Origination Authorizations...............................9 69 3.1. Role in the overall architecture..........................9 70 3.2. Syntax and semantics.....................................10 71 4. Repositories..................................................11 72 4.1. Role in the overall architecture.........................12 73 4.2. Contents and structure...................................12 74 4.3. Access protocols.........................................14 75 4.4. Access control...........................................14 76 5. Manifests.....................................................15 77 5.1. Syntax and semantics.....................................15 78 6. Local Cache Maintenance.......................................16 79 7. Common Operations.............................................17 80 7.1. Certificate issuance.....................................17 81 7.2. ROA management...........................................18 82 7.2.1. Single-homed subscribers (without provider independent 83 addresses).................................................19 84 7.2.2. Multi-homed subscribers (without provider independent 85 addresses).................................................19 86 7.2.3. Provider-Independent Address Space..................20 87 8. Security Considerations.......................................20 88 9. IANA Considerations...........................................20 89 10. Acknowledgments..............................................21 90 11. References...................................................22 91 11.1. Normative References....................................22 92 11.2. Informative References..................................22 93 Authors' Addresses...............................................23 94 Pre-5378 Material Disclaimer.....................................23 96 1. Introduction 98 This document describes an architecture for an infrastructure to 99 support improved security for BGP routing [2] for the Internet. The 100 architecture encompasses three principle elements: 102 . a public key infrastructure (PKI) 104 . digitally-signed routing objects to support routing security 106 . a distributed repository system to hold the PKI objects and the 107 signed routing objects 109 The architecture described by this document enables an entity to 110 verifiably assert that it is the legitimate holder of a set of IP 111 addresses or a set of Autonomous System (AS) numbers. As an initial 112 application of this architecture, the document describes how a 113 legitimate holder of IP address space can explicitly and verifiably 114 authorize one or more ASes to originate routes to that address space. 115 Such verifiable authorizations could be used, for example, to more 116 securely construct BGP route filters. In addition to this initial 117 application, the infrastructure defined by this architecture also is 118 intended to provide future support for security protocols such as S- 119 BGP [11] or soBGP [12]. This architecture is applicable to the 120 routing of both IPv4 and IPv6 datagrams. IPv4 and IPv6 are currently 121 the only address families supported by this architecture. Thus, for 122 example, use of this architecture with MPLS labels is beyond the 123 scope of this document. 125 In order to facilitate deployment, the architecture takes advantage 126 of existing technologies and practices. The structure of the PKI 127 element of the architecture corresponds to the existing resource 128 allocation structure. Thus management of this PKI is a natural 129 extension of the resource-management functions of the organizations 130 that are already responsible for IP address and AS number resource 131 allocation. Likewise, existing resource allocation and revocation 132 practices have well-defined correspondents in this architecture. Note 133 that while the initial focus of this architecture is routing security 134 applications, the PKI described in this document could be used to 135 support other applications that make use of attestations of IP 136 address or AS number resource holdings. 138 To ease implementation, existing IETF standards are used wherever 139 possible; for example, extensive use is made of the X.509 certificate 140 profile defined by PKIX [3] and the extensions for IP Addresses and 141 AS numbers representation defined in RFC 3779 [5]. Also CMS [4] is 142 used as the syntax for the newly-defined signed objects required by 143 this infrastructure. 145 As noted above, the architecture is comprised of three main 146 components: an X.509 PKI in which certificates attest to holdings of 147 IP address space and AS numbers; non-certificate/CRL signed objects 148 (including route origination authorizations and manifests) used by 149 the infrastructure; and a distributed repository system that makes 150 all of these signed objects available for use by ISPs in making 151 routing decisions. These three basic components enable several 152 security functions; this document describes how they can be used to 153 improve route filter generation, and to perform several other common 154 operations in such a way as to make them cryptographically 155 verifiable. 157 1.1. Terminology 159 It is assumed that the reader is familiar with the terms and concepts 160 described in "Internet X.509 Public Key Infrastructure Certificate 161 and Certificate Revocation List (CRL) Profile" [3], and "X.509 162 Extensions for IP Addresses and AS Identifiers" [5]. 164 Throughout this document we use the terms "address space holder" or 165 "holder of IP address space" interchangeably to refer to a legitimate 166 holder of IP address space who has received this address space 167 through the standard IP address allocation hierarchy. That is, the 168 address space holder has either directly received the address space 169 as an allocation from a Regional Internet Registry (RIR) or IANA; or 170 else the address space holder has received the address space as a 171 sub-allocation from a National Internet Registry (NIR) or Local 172 Internet Registry (LIR). We use the term "resource holder" to refer 173 to a legitimate holder of either IP address or AS number resources. 175 Throughout this document we use the terms "registry" and ISP to refer 176 to an entity that has an IP address space and/or AS number allocation 177 that it is permitted to sub-allocate. We use the term "subscriber" to 178 refer to an entity (e.g., an enterprise) that receives an IP address 179 space and/or AS number allocation, but does not sub-allocate its 180 resources. 182 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 183 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 184 document are to be interpreted as described in RFC-2119 [1]. 186 2. PKI for Internet Number Resources 188 Because the holder of a block IP address space is entitled to define 189 the topological destination of IP datagrams whose destinations fall 190 within that block, decisions about inter-domain routing are 191 inherently based on knowledge of the allocation of the IP address 192 space. Thus, a basic function of this architecture is to provide 193 cryptographically verifiable attestations as to these allocations. In 194 current practice, the allocation of IP addresses is hierarchic. The 195 root of the hierarchy is IANA. Below IANA are five Regional Internet 196 Registries (RIRs), each of which manages address and AS number 197 allocation within a defined geopolitical region. In some regions the 198 third tier of the hierarchy includes National Internet Registries 199 (NIRs) as well as Local Internet Registries (LIRs) and subscribers 200 with so-called provider-independent ("portable") allocations. (The 201 term LIR is used in some regions to refer to what other regions 202 define as an ISP. Throughout the rest of this document we will use 203 the term LIR/ISP to simplify references to these entities.) In other 204 regions the third tier consists only of LIRs/ISPs and subscribers 205 with provider-independent allocations. 207 In general, the holder of a block of IP address space may sub- 208 allocate portions of that block, either to itself (e.g., to a 209 particular unit of the same organization), or to another 210 organization, subject to contractual constraints established by the 211 registries. Because of this structure, IP address allocations can be 212 described naturally by a hierarchic public-key infrastructure, in 213 which each certificate attests to an allocation of IP addresses, and 214 issuance of subordinate certificates corresponds to sub-allocation of 215 IP addresses. The above reasoning holds true for AS number resources 216 as well, with the difference that, by convention, AS numbers may not 217 be sub-allocated except by RIRs or NIRs. Thus allocations of both IP 218 addresses and AS numbers can be expressed by the same PKI. Such a 219 PKI is a central component of this architecture. 221 2.1. Role in the overall architecture 223 Certificates in this PKI are called Resource Certificates, and 224 conform to the certificate profile for such certificates [6]. 225 Resource certificates attest to the allocation by the (certificate) 226 issuer of IP addresses or AS numbers to the subject. They do this by 227 binding the public key contained in the Resource Certificate to the 228 IP addresses or AS numbers included in the certificate's IP Address 229 Delegation or AS Identifier Delegation Extensions, respectively, as 230 defined in RFC 3779 [5]. 232 An important property of this PKI is that certificates do not attest 233 to the identity of the subject. Therefore, the subject names used in 234 certificates are not intended to be "descriptive." That is, the 235 resource PKI is intended to provide authorization, but not 236 authentication. This is in contrast to most PKIs where the issuer 237 ensures that the descriptive subject name in a certificate is 238 properly associated with the entity that holds the private key 239 corresponding to the public key in the certificate. Because issuers 240 need not verify the right of an entity to use a subject name in a 241 certificate, they avoid the costs and liabilities of such 242 verification. This makes it easier for these entities to take on the 243 additional role of Certificate Authority (CA). 245 Most of the certificates in the PKI assert the basic facts on which 246 the rest of the infrastructure operates. CA certificates within the 247 PKI attest to IP address space and AS number holdings. End-entity 248 (EE) certificates are issued by resource holder CAs to delegate the 249 authority attested by their allocation certificates. The primary use 250 for EE certificates is the validation of Route Origination 251 Authorizations (ROAs). Additionally, signed objects called manifests 252 will be used to help ensure the integrity of the repository system, 253 and the signature on each manifest will be verified via an EE 254 certificate. 256 2.2. CA Certificates 258 Any resource holder who is authorized to sub-allocate these resources 259 must be able to issue Resource Certificates to correspond to these 260 sub-allocations. Thus, for example, CA certificates will be 261 associated with IANA and each of the RIRs, NIRs, and LIRs/ISPs. A CA 262 certificate also is required to enable a resource holder to issue 263 ROAs, because it must issue the corresponding end-entity certificate 264 used to validate each ROA. Thus some entities that do not sub- 265 allocate their resources also will need to have CA certificates for 266 their allocations, e.g., a multi-homed subscriber with a provider- 267 independent allocation, to enable them to issue ROAs. (A subscriber 268 who is not multi-homed, whose allocation comes from an LIR/ISP, and 269 who has not moved to a different LIR/ISP, need not be represented in 270 the PKI. Moreover, a multi-homed subscriber with an allocation from 271 an LIR/ISP may or may not need to be explicitly represented, as 272 discussed in Section 7.2.2) 274 Unlike in most PKIs, the distinguished name of the subject in a CA 275 certificate is chosen by the certificate issuer. The subject's 276 distinguished name must not attempt to convey the identity of the 277 subject in a descriptive fashion. The subject's distinguished name 278 must include the common name attribute and may additionally include 279 the serial attribute. 281 In this PKI, the certificate issuer, being an RIR, NIR, or LIR/ISP, 282 is not in the business of verifying the legal right of the subject to 283 assert a particular identity. Therefore, selecting a distinguished 284 name that does not convey the identity of the subject in a 285 descriptive fashion minimizes the opportunity for the subject to 286 misuse the certificate to assert an identity, and thus minimizes the 287 legal liability of the issuer. Since all CA certificates are issued 288 to subjects with whom the issuer has an existing relationship, it is 289 recommended that the issuer select a subject name that enables the 290 issuer to easily link the certificate to existing database records 291 associated with the subject. For example, an authority may use 292 internal database keys or subscriber IDs as the subject common name 293 in issued certificates. 295 Although the subject's common name in a certificate does not convey 296 identity, it is still the case that the common name must be unique 297 among all subjects to whom a certification authority issues 298 certificates. That is, a CA must not issue certificates to two 299 different entities which use the same common name for the subject. 301 Each Resource Certificate attests to an allocation of resources to a 302 resource holder, so entities that have allocations from multiple 303 sources will have multiple CA certificates. Note that when an entity 304 receives multiple certificates from different issuers that the 305 subject names in these certificates will generally be different. A CA 306 also may issue distinct certificates for each distinct allocation to 307 the same entity, if the CA and the resource holder agree that such an 308 arrangement will facilitate management and use of the certificates. 309 For example, an LIR/ISP may have several certificates issued to it by 310 one registry, each describing a distinct set of address blocks, 311 because the LIR/ISP desires to treat the allocations as separate. 313 2.3. End-Entity (EE) Certificates 315 The private key corresponding to public key contained in an EE 316 certificate is not used to sign other certificates in a PKI. The 317 primary function of end-entity certificates in this PKI is the 318 verification of signed objects that relate to the usage of the 319 resources described in the certificate, e.g., ROAs and manifests. 320 For ROAs and manifests there will be a one-to-one correspondence 321 between end-entity certificates and signed objects, i.e., the private 322 key corresponding to each end-entity certificate is used to sign 323 exactly one object, and each object is signed with only one key. 324 This property allows the PKI to be used to revoke these signed 325 objects, rather than creating a new revocation mechanism. When the 326 end-entity certificate used to sign an object has been revoked, the 327 signature on that object (and any corresponding assertions) will be 328 considered invalid, so a signed object can be effectively revoked by 329 revoking the end-entity certificate used to sign it. 331 A secondary advantage to this one-to-one correspondence is that the 332 private key corresponding to the public key in a certificate is used 333 exactly once in its lifetime, and thus can be destroyed after it has 334 been used to sign its one object. This fact should simplify key 335 management, since there is no requirement to protect these private 336 keys for an extended period of time. 338 Although this document describes only two uses for end-entity 339 certificates, additional uses will likely be defined in the future. 340 For example, end-entity certificates could be used as a more general 341 authorization for their subjects to act on behalf of the specified 342 resource holder. This could facilitate authentication of inter-ISP 343 interactions, or authentication of interactions with the repository 344 system. These additional uses for end-entity certificates may 345 require retention of the corresponding private keys, even though this 346 is not required for the private keys associated with end-entity 347 certificates keys used for verification of ROAs and manifests, as 348 described above. 350 2.4. Trust Anchors 352 In any PKI, each relying party (RP) chooses its own set of trust 353 anchors. This general property of PKIs applies here as well. There is 354 an extant IP address space and AS number allocation hierarchy, and 355 thus IANA and/or the five RIRs are obvious candidates to be default 356 TAs here. Nonetheless, each RP ultimately chooses the set of trust 357 anchors it will use for certificate validation. 359 For example, a RP (e.g., an LIR/ISP) could create a trust anchor to 360 which all address space and/or all AS numbers are assigned, and for 361 which the RP knows the corresponding private key. The RP could then 362 issue certificates under this trust anchor to whatever entities in 363 the PKI it wishes, with the result that the certification paths 364 terminating at this locally-installed trust anchor will satisfy the 365 RFC 3779 validation requirements. A large ISP that uses private 366 (i.e., RFC 1918) IP address space and runs BGP internally will need 367 to create this sort of trust anchor to accommodate a CA to which all 368 private (RFC 1918) address space is assigned. The RP could then issue 369 certificates under this CA that correspond to the RP's internal use 370 of private address space. 372 Note that a RP who elects to create and manage its own set of trust 373 anchors may fail to detect allocation errors that arise under such 374 circumstances, but the resulting vulnerability is local to the RP. 376 It is expected that some parties within the extant IP address space 377 and AS number allocation hierarchy may wish to publish trust anchor 378 material for possible use by relying parties. A standard profile for 379 the publication of trust anchor material for this public key 380 infrastructure can be found in [9]. 382 3. Route Origination Authorizations 384 The information on IP address allocation provided by the PKI is not, 385 in itself, sufficient to guide routing decisions. In particular, BGP 386 is based on the assumption that the AS that originates routes for a 387 particular prefix is authorized to do so by the holder of that prefix 388 (or an address block encompassing the prefix); the PKI contains no 389 information about these authorizations. A Route Origination 390 Authorization (ROA) makes such authorization explicit, allowing a 391 holder of IP address space to create an object that explicitly and 392 verifiably asserts that an AS is authorized originate routes to a 393 given set of prefixes. 395 3.1. Role in the overall architecture 397 A ROA is an attestation that the holder of a set of prefixes has 398 authorized an autonomous system to originate routes for those 399 prefixes. A ROA is structured according to the format described in 400 [7]. The validity of this authorization depends on the signer of the 401 ROA being the holder of the prefix(es) in the ROA; this fact is 402 asserted by an end-entity certificate from the PKI, whose 403 corresponding private key is used to sign the ROA. 405 ROAs may be used by relying parties to verify that the AS that 406 originates a route for a given IP address prefix is authorized by the 407 holder of that prefix to originate such a route. For example, an ISP 408 might use validated ROAs as inputs to route filter construction for 409 use by its BGP routers. (See [14] for information on the use of ROAs 410 to validate the origination of BGP routes.) 412 Initially, the repository system will be the primary mechanism for 413 disseminating ROAs, since these repositories will hold the 414 certificates and CRLs needed to verify ROAs. In addition, ROAs also 415 could be distributed in BGP UPDATE messages or via other 416 communication paths, if needed to meet timeliness requirements. 418 3.2. Syntax and semantics 420 A ROA constitutes an explicit authorization for a single AS to 421 originate routes to one or more prefixes, and is signed by the holder 422 of those prefixes. A detailed specification of the ROA syntax can be 423 found in [7] but, at a high level, a ROA consists of (1) an AS 424 number; (2) a list of IP address prefixes; and, optionally, (3) for 425 each prefix, the maximum length of more specific (longer) prefixes 426 that the AS is also authorized to advertise. (This last element 427 facilitates a compact authorization to advertise, for example, any 428 prefixes of length 20 to 24 contained within a given length 20 429 prefix.) 431 Note that a ROA contains only a single AS number. Thus, if an ISP has 432 multiple AS numbers that will be authorized to originate routes to 433 the prefix(es) in the ROA, an address space holder will need to issue 434 multiple ROAs to authorize the ISP to originate routes from any of 435 these ASes. 437 A ROA is signed using the private key corresponding to the public key 438 in an end-entity certificate in the PKI. In order for a ROA to be 439 valid, its corresponding end-entity (EE) certificate must be valid 440 and the IP address prefixes of the ROA must exactly match the IP 441 address prefix(es) specified in the EE certificate's RFC 3779 442 extension. Therefore, the validity interval of the ROA is implicitly 443 the validity interval of its corresponding certificate. A ROA is 444 revoked by revoking the corresponding EE certificate. There is no 445 independent method of invoking a ROA. One might worry that this 446 revocation model could lead to long CRLs for the CA certification 447 that is signing the EE certificates. However, routing announcements 448 on the public internet are generally quite long lived. Therefore, as 449 long as the EE certificates used to verify a ROA are given a validity 450 interval of several months, the likelihood that many ROAs would need 451 to revoked within that time is quite low. 453 --------- --------- 454 | RIR | | NIR | 455 | CA | | CA | 456 --------- --------- 457 | | 458 | | 459 | | 460 --------- --------- 461 | ISP | | ISP | 462 | CA 1 | | CA 2 | 463 --------- --------- 464 | \ | 465 | ----- | 466 | \ | 467 ---------- ---------- ---------- 468 | ISP | | ISP | | ISP | 469 | EE 1a | | EE 1b | | EE 2 | 470 ---------- ---------- ---------- 471 | | | 472 | | | 473 | | | 474 ---------- ---------- ---------- 475 | ROA 1a | | ROA 1b | | ROA 2 | 476 ---------- ---------- ---------- 478 FIGURE 2: This figure illustrates an ISP with allocations from two 479 sources (and RIR and an NIR). It needs two CA certificates due to RFC 480 3779 rules. 482 Because each ROA is associated with a single end-entity certificate, 483 the set of IP prefixes contained in a ROA must be drawn from an 484 allocation by a single source, i.e., a ROA cannot combine allocations 485 from multiple sources. Address space holders who have allocations 486 from multiple sources, and who wish to authorize an AS to originate 487 routes for these allocations, must issue multiple ROAs to the AS. 489 4. Repositories 491 Initially, an LIR/ISP will make use of the resource PKI by acquiring 492 and validating every ROA, to create a table of the prefixes for which 493 each AS is authorized to originate routes. To validate all ROAs, an 494 LIR/ISP needs to acquire all the certificates and CRLs. The primary 495 function of the distributed repository system described here is to 496 store these signed objects and to make them available for download by 497 LIRs/ISPs. Note that this repository system provides a mechanism by 498 which relying parties can pull fresh data at whatever frequency they 499 deem appropriate. However, it does not provide a mechanism for 500 pushing fresh data to relying parties (e.g. by including resource PKI 501 objects in BGP or other protocol messages) and such a mechanism is 502 beyond the scope of the current document. 504 The digital signatures on all objects in the repository ensure that 505 unauthorized modification of valid objects is detectable by relying 506 parties. Additionally, the repository system uses manifests (see 507 Section 5) to ensure that relying parties can detect the deletion of 508 valid objects and the insertion of out of date, valid signed objects. 510 The repository system is also a point of enforcement for access 511 controls for the signed objects stored in it, e.g., ensuring that 512 records related to an allocation of resources can be manipulated only 513 by authorized parties. The use of access controls prevents denial of 514 service attacks based on deletion of or tampering to repository 515 objects. Indeed, although relying parties can detect tampering with 516 objects in the repository, it is preferable that the repository 517 system prevent such unauthorized modifications to the greatest extent 518 possible. 520 4.1. Role in the overall architecture 522 The repository system is the central clearing-house for all signed 523 objects that must be globally accessible to relying parties. When 524 certificates and CRLs are created, they are uploaded to this 525 repository, and then downloaded for use by relying parties (primarily 526 LIRs/ISPs). ROAs and manifests are additional examples of such 527 objects, but other types of signed objects may be added to this 528 architecture in the future. This document briefly describes the way 529 signed objects (certificates, CRLs, ROAs and manifests) are managed 530 in the repository system. As other types of signed objects are added 531 to the repository system it will be necessary to modify the 532 description, but it is anticipated that most of the design principles 533 will still apply. The repository system is described in detail in 534 [10]. 536 4.2. Contents and structure 538 Although there is a single repository system that is accessed by 539 relying parties, it is comprised of multiple databases. These 540 databases will be distributed among registries (RIRs, NIRs, 541 LIRs/ISPs). At a minimum, the database operated by each registry will 542 contain all CA and EE certificates, CRLs, and manifests signed by the 543 CA(s) associated with that registry. Repositories operated by 544 LIRs/ISPs also will contain ROAs. Registries are encouraged to 545 maintain copies of repository data from their customers, and their 546 customer's customers (etc.), to facilitate retrieval of the whole 547 repository contents by relying parties. Ideally, each RIR will hold 548 PKI data from all entities within its geopolitical scope. 550 For every certificate in the PKI, there will be a corresponding file 551 system directory in the repository that is the authoritative 552 publication point for all objects (certificates, CRLs, ROAs and 553 manifests) verifiable via this certificate. A certificate's Subject 554 Information Authority (SIA) extension provides a URI that references 555 this directory. Additionally, a certificate's Authority Information 556 Authority (AIA) extension contains a URI that references the 557 authoritative location for the CA certificate under which the given 558 certificate was issued. That is, if certificate A is used to verify 559 certificate B, then the AIA extension of certificate B points to 560 certificate A, and the SIA extension of certificate A points to a 561 directory containing certificate B (see Figure 2). 563 +--------+ 564 +--------->| Cert A |<----+ 565 | | CRLDP | | +---------+ 566 | | AIA | | +-->| A's CRL |<-+ 567 | +--------- SIA | | | +---------+ | 568 | | +--------+ | | | 569 | | | | | 570 | | +---+----+ | 571 | | | | | 572 | | +---------------|---|-----------------+ | 573 | | | | | | | 574 | +->| +--------+ | | +--------+ | | 575 | | | Cert B | | | | Cert C | | | 576 | | | CRLDP ----+ | | CRLDP -+--------+ 577 +----------- AIA | +----- AIA | | 578 | | SIA | | SIA | | 579 | +--------+ +--------+ | 580 | | 581 +-------------------------------------+ 583 FIGURE 3: In this example, certificates B and C are issued under 584 certificate A. Therefore, the AIA extensions of certificates B and C 585 point to A, and the SIA extension of certificate A points to the 586 directory containing certificates B and C. 588 If a CA certificate is reissued with the same public key, it should 589 not be necessary to reissue (with an updated AIA URI) all 590 certificates signed by the certificate being reissued. Therefore, a 591 certification authority SHOULD use a persistent URI naming scheme for 592 issued certificates. That is, reissued certificates should use the 593 same publication point as previously issued certificates having the 594 same subject and public key, and should overwrite such certificates. 596 4.3. Access protocols 598 Repository operators will choose one or more access protocols that 599 relying parties can use to access the repository system. These 600 protocols will be used by numerous participants in the infrastructure 601 (e.g., all registries, ISPs, and multi-homed subscribers) to maintain 602 their respective portions of it. In order to support these 603 activities, certain basic functionality is required of the suite of 604 access protocols, as described below. No single access protocol need 605 implement all of these functions (although this may be the case), but 606 each function must be implemented by at least one access protocol. 608 Download: Access protocols MUST support the bulk download of 609 repository contents and subsequent download of changes to the 610 downloaded contents, since this will be the most common way in which 611 relying parties interact with the repository system. Other types of 612 download interactions (e.g., download of a single object) MAY also be 613 supported. 615 Upload/change/delete: Access protocols MUST also support mechanisms 616 for the issuers of certificates, CRLs, and other signed objects to 617 add them to the repository, and to remove them. Mechanisms for 618 modifying objects in the repository MAY also be provided. All access 619 protocols that allow modification to the repository (through 620 addition, deletion, or modification of its contents) MUST support 621 verification of the authorization of the entity performing the 622 modification, so that appropriate access controls can be applied (see 623 Section 4.4). 625 Current efforts to implement a repository system use RSYNC [13] as 626 the single access protocol. RSYNC, as used in this implementation, 627 provides all of the above functionality. A document specifying the 628 conventions for use of RSYNC in the PKI will be prepared. 630 4.4. Access control 632 In order to maintain the integrity of information in the repository, 633 controls must be put in place to prevent addition, deletion, or 634 modification of objects in the repository by unauthorized parties. 635 The identities of parties attempting to make such changes can be 636 authenticated through the relevant access protocols. Although 637 specific access control policies are subject to the local control of 638 repository operators, it is recommended that repositories allow only 639 the issuers of signed objects to add, delete, or modify them. 641 Alternatively, it may be advantageous in the future to define a 642 formal delegation mechanism to allow resource holders to authorize 643 other parties to act on their behalf, as suggested in Section 2.3 644 above. 646 5. Manifests 648 A manifest is a signed object listing of all of the signed objects 649 issued by an authority responsible for a publication in the 650 repository system. For each certificate, CRL, or ROA issued by the 651 authority, the manifest contains both the name of the file containing 652 the object, and a hash of the file content. 654 As with ROAs, a manifest is signed by a private key, for which the 655 corresponding public key appears in an end-entity certificate. This 656 EE certificate, in turn, is signed by the CA in question. The EE 657 certificate private key may be used to issue one for more manifests. 658 If the private key is used to sign only a single manifest, then the 659 manifest can be revoked by revoking the EE certificate. In such a 660 case, to avoid needless CRL growth, the EE certificate used to 661 validate a manifest SHOULD expire at the same time that the manifest 662 expires. If an EE certificate is used to issue multiple (sequential) 663 manifests for the CA in question, then there is no revocation 664 mechanism for these individual manifests. 666 Manifests may be used by relying parties when constructing a local 667 cache (see Section 6) to mitigate the risk of an attacker who deletes 668 files from a repository or replaces current signed objects with stale 669 versions of the same object. Such protection is needed because 670 although all objects in the repository system are signed, the 671 repository system itself is untrusted. 673 5.1. Syntax and semantics 675 A manifest constitutes a list of (the hashes of) all the files in a 676 repository point at a particular point in time. A detailed 677 specification of manifest syntax is provided in [8] but, at a high 678 level, a manifest consists of (1) a manifest number; (2) the time the 679 manifest was issued; (3) the time of the next planned update; and (4) 680 a list of filename and hash value pairs. 682 The manifest number is a sequence number that is incremented each 683 time a manifest is issued by the authority. An authority is required 684 to issue a new manifest any time it alters any of its items in the 685 repository, or when the specified time of the next update is reached. 686 A manifest is thus valid until the specified time of the next update 687 or until a manifest is issued with a greater manifest number, 688 whichever comes first. (Note that when an EE certificate is used to 689 sign only a single manifest, whenever the authority issues the new 690 manifest, the CA MUST also issue a new CRL which includes the EE 691 certificate corresponding to the old manifest. The revoked EE 692 certificate for the old manifest will be removed from the CRL when it 693 expires, thus this procedure ought not to result in significant CRLs 694 growth.) 696 6. Local Cache Maintenance 698 In order to utilize signed objects issued under this PKI, a relying 699 party must first obtain a local copy of the valid EE certificates for 700 the PKI. To do so, the relying party performs the following steps: 702 1. Query the registry system to obtain a copy of all certificates, 703 manifests and CRLs issued under the PKI. 705 2. For each CA certificate in the PKI, verify the signature on the 706 corresponding manifest. Additionally, verify that the current 707 time is earlier than the time indicated in the nextUpdate field 708 of the manifest. 710 3. For each manifest, verify that certificates and CRLs issued 711 under the corresponding CA certificate match the hash values 712 contained in the manifest. Additionally, verify that no 713 certificate or manifest listed on the manifest is missing from 714 the repository. If the hash values do not match, or if any 715 certificate or CRL is missing, notify the appropriate repository 716 administrator that the repository data has been corrupted. 718 4. Validate each EE certificate by constructing and verifying a 719 certification path for the certificate (including checking 720 relevant CRLs) to the locally configured set of TAs. (See [6] 721 for more details.) 723 Note that when a relying party performs these operations regularly, 724 it is more efficient for the relying party to request from the 725 repository system only those objects that have changed since the 726 relying party last updated its local cache. A relying party may 727 choose any frequency it desires for downloading and validating 728 updates from the repository. However, a typical ISP might reasonably 729 choose to perform these operations on a daily schedule. Note also 730 that by checking all issued objects against the appropriate manifest, 731 the relying party can be certain that it is not missing an updated 732 version of any object. 734 7. Common Operations 736 Creating and maintaining the infrastructure described above will 737 entail additional operations as "side effects" of normal resource 738 allocation and routing authorization procedures. For example, a 739 subscriber with provider-independent ("portable") address space who 740 enters a relationship with an ISP will need to issue one or more ROAs 741 identifying that ISP, in addition to conducting any other necessary 742 technical or business procedures. The current primary use of this 743 infrastructure is for route filter construction; using ROAs, route 744 filters can be constructed in an automated fashion with high 745 assurance that the holder of the advertised prefix has authorized the 746 origin AS to originate an advertised route. 748 7.1. Certificate issuance 750 There are several operational scenarios that require certificates to 751 be issued. Any allocation that may be sub-allocated requires a CA 752 certificate, e.g., so that certificates can be issued as necessary 753 for the sub-allocations. Holders of provider-independent IP address 754 space allocations also must have certificates, so that a ROA can be 755 issued to each ISP that is authorized to originate a route to the 756 allocation (since the allocation does not come from any ISP). 757 Additionally, multi-homed subscribers may require certificates for 758 their allocations if they intend to issue the ROAs for their 759 allocations (see Section 7.2.2). Other resource holders need not be 760 issued CA certificates within the PKI. 762 In the long run, a resource holder will not request resource 763 certificates, but rather receive a certificate as a side effect of 764 the allocation process for the resource. However, initial deployment 765 of the RPKI will entail issuance of certificates to existing resource 766 holders as an explicit event. Note that in all cases, the authority 767 issuing a CA certificate will be the entity who allocates resources 768 to the subject. This differs from most PKIs in which a subject can 769 request a certificate from any certification authority. 771 If a resource holder receives multiple allocations over time, it may 772 accrue a collection of resource certificates to attest to them. If a 773 resource holder receives multiple allocations from the same source, 774 the set of resource certificates may be combined into a single 775 resource certificate, if both the issuer and the resource holder 776 agree. This is accomplished by consolidating the IP Address 777 Delegation and AS Identifier Delegation Extensions into a single 778 extension (of each type) in a new certificate. However, if the 779 certificates for these allocations contain different validity 780 intervals, creating a certificate that combines them might create 781 problems, and thus is NOT RECOMMENDED. 783 If a resource holder's allocations come from different sources, they 784 will be signed by different CAs, and cannot be combined. When a set 785 of resources is no longer allocated to a resource holder, any 786 certificates attesting to such an allocation MUST be revoked. A 787 resource holder SHOULD NOT use the same public key in multiple CA 788 certificates that are issued by the same or differing authorities, as 789 reuse of a key pair complicates path construction. Note that since 790 the subject's distinguished name is chosen by the issuer, a subject 791 who receives allocations from two sources generally will receive 792 certificates with different subject names. 794 7.2. ROA management 796 Whenever a holder of IP address space wants to authorize an AS to 797 originate routes for a prefix within his holdings, he MUST issue an 798 end-entity certificate containing that prefix in an IP Address 799 Delegation extension. He then uses the corresponding private key to 800 sign a ROA containing the designated prefix and the AS number for the 801 AS. The resource holder MAY include more than one prefix in the EE 802 certificate and corresponding ROA if desired. As a prerequisite, 803 then, any address space holder that issues ROAs for a prefix must 804 have a resource certificate for an allocation containing that prefix. 805 The standard procedure for issuing a ROA is as follows: 807 1. Create an end-entity certificate containing the prefix(es) to be 808 authorized in the ROA. 810 2. Construct the payload of the ROA, including the prefixes in the 811 end-entity certificate and the AS number to be authorized. 813 3. Sign the ROA using the private key corresponding to the end- 814 entity certificate (the ROA is comprised of the payload 815 encapsulated in a CMS signed message [7]). 817 4. Upload the end-entity certificate and the ROA to the repository 818 system. 820 The standard procedure for revoking a ROA is to revoke the 821 corresponding end-entity certificate by creating an appropriate CRL 822 and uploading it to the repository system. The revoked ROA and end- 823 entity certificate SHOULD BE removed from the repository system. 825 Care must be taken when revoking ROAs in that revoking a ROA may 826 cause a relying party to treat routing advertisements corresponding 827 to the prefixes and origin AS number in the ROA as unauthorized (and 828 potentially even change routing behavior to no longer forward packets 829 based on those advertisements). In particular, resource holders 830 should adhere to the principle of "make before break" as follows. 831 Before revoking a ROA corresponding to a prefix which the resource 832 holder wishes to be routable on the Internet, it is very important 833 for the resource holder to ensure that there exists another valid 834 alternative ROA that lists the same prefix (possibly indicating a 835 different AS number). Additionally, the resource holder should ensure 836 that the AS indicated in the valid alternative ROA is actually 837 originating routing advertisements to the prefixes in question. 838 Furthermore, a relying party must fetch new ROAs from the repository 839 system before taking any routing action in response to a ROA 840 revocation. 842 7.2.1. Single-homed subscribers (without provider independent addresses) 844 In BGP, a single-homed subscriber with provider allocated (non- 845 portable) address space does not need to explicitly authorize routes 846 to be originated for the prefix(es) it is using, since its ISP will 847 already advertise a more general prefix and route traffic for the 848 subscriber's prefix as an internal function. Since no routes are 849 originated specifically for prefixes held by these subscribers, no 850 ROAs need to be issued under their allocations; rather, the 851 subscriber's ISP will issue any necessary ROAs for its more general 852 prefixes under resource certificates from its own allocation. Thus, a 853 single-homed subscriber with an IP address allocation from his 854 service provider is not included in the RPKI, i.e., it does not 855 receive a CA certificate, nor issue EE certificates or ROAs. 857 7.2.2. Multi-homed subscribers (without provider independent addresses) 859 Here we consider a subscriber who receives IP address space from a 860 primary ISP (i.e., the IP addresses used by the subscriber are a 861 subset of ISP A's IP address space allocation) and receives redundant 862 upstream connectivity from the primary ISP, as well as one or more 863 secondary ISPs. The preferred option for such a multi-homed 864 subscribers is for the subscriber to obtain an AS number (from an RIR 865 or NIR) and run BGP with each of its upstream providers. In such a 866 case, there are two ways for ROA management to be handled. The first 867 is that the primary ISP issues a CA certificate to the subscriber, 868 and the subscriber issues a ROA to containing the subscriber's AS 869 number and the subscriber's IP address prefixes. The second 870 possibility is that the primary ISP does not issue a ROA to the 871 subscriber, and instead issues a ROA on the subscriber's behalf that 872 contains the subscriber's AS number and the subscriber's IP address 873 prefixes. 875 If the subscriber is unable or unwilling to obtain an AS number and 876 run BGP, the other option is that the multi-homed subscriber can 877 request that the primary ISP create a ROA for each secondary ISP that 878 authorizes the secondary ISP to originate routes to the subscriber's 879 prefixes. The primary ISP will also create a ROA containing its own 880 AS number and the subscriber's prefixes, as it is likely in such a 881 case that the primary ISP wishes to advertise precisely the 882 subscriber's prefixes and not an encompassing aggregate. Note that 883 this approach results in inconsistent origin AS numbers for the 884 subscribers prefixes which are considered undesirable on the public 885 Internet; thus this approach is NOT RECOMMENDED. 887 7.2.3. Provider-Independent Address Space 889 A resource holder is said to have provider-independent (portable) 890 address space if the resource holder received its allocation directly 891 from a RIR or NIR. Because the prefixes represented in such 892 allocations are not taken from an allocation held by an ISP, there is 893 no ISP that holds and advertises a more general prefix. A holder of a 894 portable IP address space allocation MUST authorize one or more ASes 895 to originate routes to these prefixes. Thus the resource holder MUST 896 generate one or more EE certificates and associated ROAs to enable 897 the AS(es) to originate routes for the prefix(es) in question. This 898 ROA is required because none of the ISP's existing ROAs authorize it 899 to originate routes to the subscriber's provider-idependent 900 allocation. 902 8. Security Considerations 904 The focus of this document is security; hence security considerations 905 permeate this specification. 907 The security mechanisms provided by and enabled by this architecture 908 depend on the integrity and availability of the infrastructure it 909 describes. The integrity of objects within the infrastructure is 910 ensured by appropriate controls on the repository system, as 911 described in Section 4.4. Likewise, because the repository system is 912 structured as a distributed database, it should be inherently 913 resistant to denial of service attacks; nonetheless, appropriate 914 precautions should also be taken, both through replication and backup 915 of the constituent databases and through the physical security of 916 database servers. 918 9. IANA Considerations 920 This document requests that the IANA issue RPKI Certificates for the 921 resources for which it is authoritative, i.e., reserved IPv4 922 addresses, IPv6 ULAs, and address space not yet allocated by IANA to 923 the RIRs. IANA SHOULD make available trust anchor material in the 924 format defined in [10] in support of these functions. 926 10. Acknowledgments 928 The architecture described in this draft is derived from the 929 collective ideas and work of a large group of individuals. This work 930 would not have been possible without the intellectual contributions 931 of George Michaelson, Robert Loomans, Sanjaya and Geoff Huston of 932 APNIC, Robert Kisteleki and Henk Uijterwaal of the RIPE NCC, Tim 933 Christensen and Cathy Murphy of ARIN, Rob Austein of ISC and Randy 934 Bush of IIJ. 936 Although we are indebted to everyone who has contributed to this 937 architecture, we would like to especially thank Rob Austein for the 938 concept of a manifest, Geoff Huston for the concept of managing 939 object validity through single-use EE certificate key pairs, and 940 Richard Barnes for help in preparing an early version of this 941 document. 943 11. References 945 11.1. Normative References 947 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 948 Levels", BCP 14, RFC 2119, March 1997. 950 [2] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 951 (BGP-4)", RFC 4271, January 2006 953 [3] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, 954 R., and W. Polk, "Internet X.509 Public Key Infrastructure 955 Certificate and Certificate Revocation List (CRL) Profile", RFC 956 5280, May 2008. 958 [4] Housley, R., "Cryptographic Message Syntax", RFC 3852, July 959 2004. 961 [5] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP 962 Addresses and AS Identifiers", RFC 3779, June 2004. 964 [6] Huston, G., Michaelson, G., and Loomans, R., "A Profile for 965 X.509 PKIX Resource Certificates", draft-ietf-sidr-res-certs- 966 16, February 2009. 968 [7] Lepinski, M., Kent, S., and Kong, D., "A Profile for Route 969 Origin Authorizations (ROA)", draft-ietf-sidr-roa-format-04, 970 November 2008. 972 [8] Austein, R., et al., "Manifests for the Resource Public Key 973 Infrastructure", draft-ietf-sidr-rpki-manifests-04, October 974 2008. 976 [9] Michaelson, G., Kent, S., and Huston, G., "A Profile for Trust 977 Anchor Material for the Resource Certificate PKI", draft-ietf- 978 sidr-ta-00, February 2009. 980 11.2. Informative References 982 [10] Huston, G., Michaelson, G., and Loomans, R., "A Profile for 983 Resource Certificate Repository Structure", draft-ietf-sidr- 984 repos-struct-01, October 2008. 986 [11] Kent, S., Lynn, C., and Seo, K., "Secure Border Gateway 987 Protocol (Secure-BGP)", IEEE Journal on Selected Areas in 988 Communications Vol. 18, No. 4, April 2000. 990 [12] White, R., "soBGP", May 2005, 993 [13] Tridgell, A., "rsync", April 2006, 994 996 [14] Huston, G., Michaelson, G., "Validation of Route Origination in 997 BGP using the Resource Certificate PKI", draft-ietf-sidr-roa- 998 validation-01, October 2008. 1000 Authors' Addresses 1002 Matt Lepinski 1003 BBN Technologies 1004 10 Moulton St. 1005 Cambridge, MA 02138 1007 Email: mlepinski@bbn.com 1009 Stephen Kent 1010 BBN Technologies 1011 10 Moulton St. 1012 Cambridge, MA 02138 1014 Email: kent@bbn.com 1016 Pre-5378 Material Disclaimer 1018 This document may contain material from IETF Documents or IETF 1019 Contributions published or made publicly available before November 1020 10, 2008. The person(s) controlling the copyright in some of this 1021 material may not have granted the IETF Trust the right to allow 1022 modifications of such material outside the IETF Standards Process. 1023 Without obtaining an adequate license from the person(s) controlling 1024 the copyright in such materials, this document may not be modified 1025 outside the IETF Standards Process, and derivative works of it may 1026 not be created outside the IETF Standards Process, except to format 1027 it for publication as an RFC or to translate it into languages other 1028 than English.