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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 13, 2009 5 Expires: January 13, 2010 7 An Infrastructure to Support Secure Internet Routing 8 draft-ietf-sidr-arch-07.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 13, 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 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......................................9 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..............................................20 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, this PKI 235 is intended to provide authorization, but not authentication. This is 236 in contrast to most PKIs where the issuer ensures that the 237 descriptive subject name in a certificate is properly associated with 238 the entity that holds the private key corresponding to the public key 239 in the certificate. Because issuers need not verify the right of an 240 entity to use a subject name in a certificate, they avoid the costs 241 and liabilities of such verification. This makes it easier for these 242 entities to take on the additional role of Certificate Authority 243 (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, and must be unique among all 278 certificates issued by a given authority. The subject's distinguished 279 name must include the common name attribute and may additionally 280 include the serial attribute. 282 In this PKI, the certificate issuer, being an RIR, NIR, or LIR/ISP, 283 is not in the business of verifying the legal right of the subject to 284 assert a particular identity. Therefore, selecting a distinguished 285 name that does not convey the identity of the subject in a 286 descriptive fashion minimizes the opportunity for the subject to 287 misuse the certificate to assert an identity, and thus minimizes the 288 legal liability of the issuer. Since all CA certificates are issued 289 to subjects with whom the issuer has an existing relationship, it is 290 recommended that the issuer select a subject name that enables the 291 issuer to easily link the certificate to existing database records 292 associated with the subject. For example, an authority may use 293 internal database keys or subscriber IDs as the subject common name 294 in issued certificates. 296 Each Resource Certificate attests to an allocation of resources to a 297 resource holder, so entities that have allocations from multiple 298 sources will have multiple CA certificates. A CA also may issue 299 distinct certificates for each distinct allocation to the same 300 entity, if the CA and the resource holder agree that such an 301 arrangement will facilitate management and use of the certificates. 302 For example, an LIR/ISP may have several certificates issued to it by 303 one registry, each describing a distinct set of address blocks, 304 because the LIR/ISP desires to treat the allocations as separate. 306 2.3. End-Entity (EE) Certificates 308 The private key corresponding to public key contained in an EE 309 certificate is not used to sign other certificates in a PKI. The 310 primary function of end-entity certificates in this PKI is the 311 verification of signed objects that relate to the usage of the 312 resources described in the certificate, e.g., ROAs and manifests. 313 For ROAs and manifests there will be a one-to-one correspondence 314 between end-entity certificates and signed objects, i.e., the private 315 key corresponding to each end-entity certificate is used to sign 316 exactly one object, and each object is signed with only one key. 317 This property allows the PKI to be used to revoke these signed 318 objects, rather than creating a new revocation mechanism. When the 319 end-entity certificate used to sign an object has been revoked, the 320 signature on that object (and any corresponding assertions) will be 321 considered invalid, so a signed object can be effectively revoked by 322 revoking the end-entity certificate used to sign it. 324 A secondary advantage to this one-to-one correspondence is that the 325 private key corresponding to the public key in a certificate is used 326 exactly once in its lifetime, and thus can be destroyed after it has 327 been used to sign its one object. This fact should simplify key 328 management, since there is no requirement to protect these private 329 keys for an extended period of time. 331 Although this document describes only two uses for end-entity 332 certificates, additional uses will likely be defined in the future. 333 For example, end-entity certificates could be used as a more general 334 authorization for their subjects to act on behalf of the specified 335 resource holder. This could facilitate authentication of inter-ISP 336 interactions, or authentication of interactions with the repository 337 system. These additional uses for end-entity certificates may 338 require retention of the corresponding private keys, even though this 339 is not required for the private keys associated with end-entity 340 certificates keys used for verification of ROAs and manifests, as 341 described above. 343 2.4. Trust Anchors 345 In any PKI, each relying party (RP) chooses its own set of trust 346 anchors. This general property of PKIs applies here as well. There is 347 an extant IP address space and AS number allocation hierarchy, and 348 thus IANA and/or the five RIRs are obvious candidates to be default 349 TAs here. Nonetheless, each RP ultimately chooses the set of trust 350 anchors it will use for certificate validation. 352 For example, a RP (e.g., an LIR/ISP) could create a trust anchor to 353 which all address space and/or all AS numbers are assigned, and for 354 which the RP knows the corresponding private key. The RP could then 355 issue certificates under this trust anchor to whatever entities in 356 the PKI it wishes, with the result that the certification paths 357 terminating at this locally-installed trust anchor will satisfy the 358 RFC 3779 validation requirements. A large ISP that uses private 359 (i.e., RFC 1918) IP address space and runs BGP internally will need 360 to create this sort of trust anchor to accommodate a CA to which all 361 private (RFC 1918) address space is assigned. The RP could then issue 362 certificates under this CA that correspond to the RP's internal use 363 of private address space. 365 Note that a RP who elects to create and manage its own set of trust 366 anchors may fail to detect allocation errors that arise under such 367 circumstances, but the resulting vulnerability is local to the RP. 369 It is expected that some parties within the extant IP address space 370 and AS number allocation hierarchy may wish to publish trust anchor 371 material for possible use by relying parties. A standard profile for 372 the publication of trust anchor material for this public key 373 infrastructure can be found in [9]. 375 3. Route Origination Authorizations 377 The information on IP address allocation provided by the PKI is not, 378 in itself, sufficient to guide routing decisions. In particular, BGP 379 is based on the assumption that the AS that originates routes for a 380 particular prefix is authorized to do so by the holder of that prefix 381 (or an address block encompassing the prefix); the PKI contains no 382 information about these authorizations. A Route Origination 383 Authorization (ROA) makes such authorization explicit, allowing a 384 holder of IP address space to create an object that explicitly and 385 verifiably asserts that an AS is authorized originate routes to a 386 given set of prefixes. 388 3.1. Role in the overall architecture 390 A ROA is an attestation that the holder of a set of prefixes has 391 authorized an autonomous system to originate routes for those 392 prefixes. A ROA is structured according to the format described in 393 [7]. The validity of this authorization depends on the signer of the 394 ROA being the holder of the prefix(es) in the ROA; this fact is 395 asserted by an end-entity certificate from the PKI, whose 396 corresponding private key is used to sign the ROA. 398 ROAs may be used by relying parties to verify that the AS that 399 originates a route for a given IP address prefix is authorized by the 400 holder of that prefix to originate such a route. For example, an ISP 401 might use validated ROAs as inputs to route filter construction for 402 use by its BGP routers. (See [14] for information on the use of ROAs 403 to validate the origination of BGP routes.) 405 Initially, the repository system will be the primary mechanism for 406 disseminating ROAs, since these repositories will hold the 407 certificates and CRLs needed to verify ROAs. In addition, ROAs also 408 could be distributed in BGP UPDATE messages or via other 409 communication paths, if needed to meet timeliness requirements. 411 3.2. Syntax and semantics 413 A ROA constitutes an explicit authorization for a single AS to 414 originate routes to one or more prefixes, and is signed by the holder 415 of those prefixes. A detailed specification of the ROA syntax can be 416 found in [7] but, at a high level, a ROA consists of (1) an AS 417 number; (2) a list of IP address prefixes; and, optionally, (3) for 418 each prefix, the maximum length of more specific (longer) prefixes 419 that the AS is also authorized to advertise. (This last element 420 facilitates a compact authorization to advertise, for example, any 421 prefixes of length 20 to 24 contained within a given length 20 422 prefix.) 424 Note that a ROA contains only a single AS number. Thus, if an ISP has 425 multiple AS numbers that will be authorized to originate routes to 426 the prefix(es) in the ROA, an address space holder will need to issue 427 multiple ROAs to authorize the ISP to originate routes from any of 428 these ASes. 430 A ROA is signed using the private key corresponding to the public key 431 in an end-entity certificate in the PKI. In order for a ROA to be 432 valid, its corresponding end-entity (EE) certificate must be valid 433 and the IP address prefixes of the ROA must exactly match the IP 434 address prefix(es) specified in the EE certificate's RFC 3779 435 extension. Therefore, the validity interval of the ROA is implicitly 436 the validity interval of its corresponding certificate. A ROA is 437 revoked by revoking the corresponding EE certificate. There is no 438 independent method of invoking a ROA. One might worry that this 439 revocation model could lead to long CRLs for the CA certification 440 that is signing the EE certificates. However, routing announcements 441 on the public internet are generally quite long lived. Therefore, as 442 long as the EE certificates used to verify a ROA are given a validity 443 interval of several months, the likelihood that many ROAs would need 444 to revoked within that time is quite low. 446 --------- --------- 447 | RIR | | NIR | 448 | CA | | CA | 449 --------- --------- 450 | | 451 | | 452 | | 453 --------- --------- 454 | ISP | | ISP | 455 | CA 1 | | CA 2 | 456 --------- --------- 457 | \ | 458 | ----- | 459 | \ | 460 ---------- ---------- ---------- 461 | ISP | | ISP | | ISP | 462 | EE 1a | | EE 1b | | EE 2 | 463 ---------- ---------- ---------- 464 | | | 465 | | | 466 | | | 467 ---------- ---------- ---------- 468 | ROA 1a | | ROA 1b | | ROA 2 | 469 ---------- ---------- ---------- 471 FIGURE 2: This figure illustrates an ISP with allocations from two 472 sources (and RIR and an NIR). It needs two CA certificates due to RFC 473 3779 rules. 475 Because each ROA is associated with a single end-entity certificate, 476 the set of IP prefixes contained in a ROA must be drawn from an 477 allocation by a single source, i.e., a ROA cannot combine allocations 478 from multiple sources. Address space holders who have allocations 479 from multiple sources, and who wish to authorize an AS to originate 480 routes for these allocations, must issue multiple ROAs to the AS. 482 4. Repositories 484 Initially, an LIR/ISP will make use of the resource PKI by acquiring 485 and validating every ROA, to create a table of the prefixes for which 486 each AS is authorized to originate routes. To validate all ROAs, an 487 LIR/ISP needs to acquire all the certificates and CRLs. The primary 488 function of the distributed repository system described here is to 489 store these signed objects and to make them available for download by 490 LIRs/ISPs. Note that this repository system provides a mechanism by 491 which relying parties can pull fresh data at whatever frequency they 492 deem appropriate. However, it does not provide a mechanism for 493 pushing fresh data to relying parties (e.g. by including resource PKI 494 objects in BGP or other protocol messages) and such a mechanism is 495 beyond the scope of the current document. 497 The digital signatures on all objects in the repository ensure that 498 unauthorized modification of valid objects is detectable by relying 499 parties. Additionally, the repository system uses manifests (see 500 Section 5) to ensure that relying parties can detect the deletion of 501 valid objects and the insertion of out of date, valid signed objects. 503 The repository system is also a point of enforcement for access 504 controls for the signed objects stored in it, e.g., ensuring that 505 records related to an allocation of resources can be manipulated only 506 by authorized parties. The use of access controls prevents denial of 507 service attacks based on deletion of or tampering to repository 508 objects. Indeed, although relying parties can detect tampering with 509 objects in the repository, it is preferable that the repository 510 system prevent such unauthorized modifications to the greatest extent 511 possible. 513 4.1. Role in the overall architecture 515 The repository system is the central clearing-house for all signed 516 objects that must be globally accessible to relying parties. When 517 certificates and CRLs are created, they are uploaded to this 518 repository, and then downloaded for use by relying parties (primarily 519 LIRs/ISPs). ROAs and manifests are additional examples of such 520 objects, but other types of signed objects may be added to this 521 architecture in the future. This document briefly describes the way 522 signed objects (certificates, CRLs, ROAs and manifests) are managed 523 in the repository system. As other types of signed objects are added 524 to the repository system it will be necessary to modify the 525 description, but it is anticipated that most of the design principles 526 will still apply. The repository system is described in detail in 527 [10]. 529 4.2. Contents and structure 531 Although there is a single repository system that is accessed by 532 relying parties, it is comprised of multiple databases. These 533 databases will be distributed among registries (RIRs, NIRs, 534 LIRs/ISPs). At a minimum, the database operated by each registry will 535 contain all CA and EE certificates, CRLs, and manifests signed by the 536 CA(s) associated with that registry. Repositories operated by 537 LIRs/ISPs also will contain ROAs. Registries are encouraged to 538 maintain copies of repository data from their customers, and their 539 customer's customers (etc.), to facilitate retrieval of the whole 540 repository contents by relying parties. Ideally, each RIR will hold 541 PKI data from all entities within its geopolitical scope. 543 For every certificate in the PKI, there will be a corresponding file 544 system directory in the repository that is the authoritative 545 publication point for all objects (certificates, CRLs, ROAs and 546 manifests) verifiable via this certificate. A certificate's Subject 547 Information Authority (SIA) extension provides a URI that references 548 this directory. Additionally, a certificate's Authority Information 549 Authority (AIA) extension contains a URI that references the 550 authoritative location for the CA certificate under which the given 551 certificate was issued. That is, if certificate A is used to verify 552 certificate B, then the AIA extension of certificate B points to 553 certificate A, and the SIA extension of certificate A points to a 554 directory containing certificate B (see Figure 2). 556 +--------+ 557 +--------->| Cert A |<----+ 558 | | CRLDP | | +---------+ 559 | | AIA | | +-->| A's CRL |<-+ 560 | +--------- SIA | | | +---------+ | 561 | | +--------+ | | | 562 | | | | | 563 | | +---+----+ | 564 | | | | | 565 | | +---------------|---|-----------------+ | 566 | | | | | | | 567 | +->| +--------+ | | +--------+ | | 568 | | | Cert B | | | | Cert C | | | 569 | | | CRLDP ----+ | | CRLDP -+--------+ 570 +----------- AIA | +----- AIA | | 571 | | SIA | | SIA | | 572 | +--------+ +--------+ | 573 | | 574 +-------------------------------------+ 576 FIGURE 3: In this example, certificates B and C are issued under 577 certificate A. Therefore, the AIA extensions of certificates B and C 578 point to A, and the SIA extension of certificate A points to the 579 directory containing certificates B and C. 581 If a CA certificate is reissued with the same public key, it should 582 not be necessary to reissue (with an updated AIA URI) all 583 certificates signed by the certificate being reissued. Therefore, a 584 certification authority SHOULD use a persistent URI naming scheme for 585 issued certificates. That is, reissued certificates should use the 586 same publication point as previously issued certificates having the 587 same subject and public key, and should overwrite such certificates. 589 4.3. Access protocols 591 Repository operators will choose one or more access protocols that 592 relying parties can use to access the repository system. These 593 protocols will be used by numerous participants in the infrastructure 594 (e.g., all registries, ISPs, and multi-homed subscribers) to maintain 595 their respective portions of it. In order to support these 596 activities, certain basic functionality is required of the suite of 597 access protocols, as described below. No single access protocol need 598 implement all of these functions (although this may be the case), but 599 each function must be implemented by at least one access protocol. 601 Download: Access protocols MUST support the bulk download of 602 repository contents and subsequent download of changes to the 603 downloaded contents, since this will be the most common way in which 604 relying parties interact with the repository system. Other types of 605 download interactions (e.g., download of a single object) MAY also be 606 supported. 608 Upload/change/delete: Access protocols MUST also support mechanisms 609 for the issuers of certificates, CRLs, and other signed objects to 610 add them to the repository, and to remove them. Mechanisms for 611 modifying objects in the repository MAY also be provided. All access 612 protocols that allow modification to the repository (through 613 addition, deletion, or modification of its contents) MUST support 614 verification of the authorization of the entity performing the 615 modification, so that appropriate access controls can be applied (see 616 Section 4.4). 618 Current efforts to implement a repository system use RSYNC [13] as 619 the single access protocol. RSYNC, as used in this implementation, 620 provides all of the above functionality. A document specifying the 621 conventions for use of RSYNC in the PKI will be prepared. 623 4.4. Access control 625 In order to maintain the integrity of information in the repository, 626 controls must be put in place to prevent addition, deletion, or 627 modification of objects in the repository by unauthorized parties. 628 The identities of parties attempting to make such changes can be 629 authenticated through the relevant access protocols. Although 630 specific access control policies are subject to the local control of 631 repository operators, it is recommended that repositories allow only 632 the issuers of signed objects to add, delete, or modify them. 634 Alternatively, it may be advantageous in the future to define a 635 formal delegation mechanism to allow resource holders to authorize 636 other parties to act on their behalf, as suggested in Section 2.3 637 above. 639 5. Manifests 641 A manifest is a signed object listing of all of the signed objects 642 issued by an authority responsible for a publication in the 643 repository system. For each certificate, CRL, or ROA issued by the 644 authority, the manifest contains both the name of the file containing 645 the object, and a hash of the file content. 647 As with ROAs, a manifest is signed by a private key, for which the 648 corresponding public key appears in an end-entity certificate. This 649 EE certificate, in turn, is signed by the CA in question. The EE 650 certificate private key may be used to issue one for more manifests. 651 If the private key is used to sign only a single manifest, then the 652 manifest can be revoked by revoking the EE certificate. In such a 653 case, to avoid needless CRL growth, the EE certificate used to 654 validate a manifest SHOULD expire at the same time that the manifest 655 expires. If an EE certificate is used to issue multiple (sequential) 656 manifests for the CA in question, then there is no revocation 657 mechanism for these individual manifests. 659 Manifests may be used by relying parties when constructing a local 660 cache (see Section 6) to mitigate the risk of an attacker who deletes 661 files from a repository or replaces current signed objects with stale 662 versions of the same object. Such protection is needed because 663 although all objects in the repository system are signed, the 664 repository system itself is untrusted. 666 5.1. Syntax and semantics 668 A manifest constitutes a list of (the hashes of) all the files in a 669 repository point at a particular point in time. A detailed 670 specification of manifest syntax is provided in [8] but, at a high 671 level, a manifest consists of (1) a manifest number; (2) the time the 672 manifest was issued; (3) the time of the next planned update; and (4) 673 a list of filename and hash value pairs. 675 The manifest number is a sequence number that is incremented each 676 time a manifest is issued by the authority. An authority is required 677 to issue a new manifest any time it alters any of its items in the 678 repository, or when the specified time of the next update is reached. 679 A manifest is thus valid until the specified time of the next update 680 or until a manifest is issued with a greater manifest number, 681 whichever comes first. (Note that when an EE certificate is used to 682 sign only a single manifest, whenever the authority issues the new 683 manifest, the CA MUST also issue a new CRL which includes the EE 684 certificate corresponding to the old manifest. The revoked EE 685 certificate for the old manifest will be removed from the CRL when it 686 expires, thus this procedure ought not to result in significant CRLs 687 growth.) 689 6. Local Cache Maintenance 691 In order to utilize signed objects issued under this PKI, a relying 692 party must first obtain a local copy of the valid EE certificates for 693 the PKI. To do so, the relying party performs the following steps: 695 1. Query the registry system to obtain a copy of all certificates, 696 manifests and CRLs issued under the PKI. 698 2. For each CA certificate in the PKI, verify the signature on the 699 corresponding manifest. Additionally, verify that the current 700 time is earlier than the time indicated in the nextUpdate field 701 of the manifest. 703 3. For each manifest, verify that certificates and CRLs issued 704 under the corresponding CA certificate match the hash values 705 contained in the manifest. Additionally, verify that no 706 certificate or manifest listed on the manifest is missing from 707 the repository. If the hash values do not match, or if any 708 certificate or CRL is missing, notify the appropriate repository 709 administrator that the repository data has been corrupted. 711 4. Validate each EE certificate by constructing and verifying a 712 certification path for the certificate (including checking 713 relevant CRLs) to the locally configured set of TAs. (See [6] 714 for more details.) 716 Note that when a relying party performs these operations regularly, 717 it is more efficient for the relying party to request from the 718 repository system only those objects that have changed since the 719 relying party last updated its local cache. A relying party may 720 choose any frequency it desires for downloading and validating 721 updates from the repository. However, a typical ISP might reasonably 722 choose to perform these operations on a daily schedule. Note also 723 that by checking all issued objects against the appropriate manifest, 724 the relying party can be certain that it is not missing an updated 725 version of any object. 727 7. Common Operations 729 Creating and maintaining the infrastructure described above will 730 entail additional operations as "side effects" of normal resource 731 allocation and routing authorization procedures. For example, a 732 subscriber with provider-independent ("portable") address space who 733 enters a relationship with an ISP will need to issue one or more ROAs 734 identifying that ISP, in addition to conducting any other necessary 735 technical or business procedures. The current primary use of this 736 infrastructure is for route filter construction; using ROAs, route 737 filters can be constructed in an automated fashion with high 738 assurance that the holder of the advertised prefix has authorized the 739 origin AS to originate an advertised route. 741 7.1. Certificate issuance 743 There are several operational scenarios that require certificates to 744 be issued. Any allocation that may be sub-allocated requires a CA 745 certificate, e.g., so that certificates can be issued as necessary 746 for the sub-allocations. Holders of provider-independent IP address 747 space allocations also must have certificates, so that a ROA can be 748 issued to each ISP that is authorized to originate a route to the 749 allocation (since the allocation does not come from any ISP). 750 Additionally, multi-homed subscribers may require certificates for 751 their allocations if they intend to issue the ROAs for their 752 allocations (see Section 7.2.2). Other resource holders need not be 753 issued CA certificates within the PKI. 755 In the long run, a resource holder will not request resource 756 certificates, but rather receive a certificate as a side effect of 757 the allocation process for the resource. However, initial deployment 758 of the RPKI will entail issuance of certificates to existing resource 759 holders as an explicit event. Note that in all cases, the authority 760 issuing a CA certificate will be the entity who allocates resources 761 to the subject. This differs from most PKIs in which a subject can 762 request a certificate from any certification authority. 764 If a resource holder receives multiple allocations over time, it may 765 accrue a collection of resource certificates to attest to them. If a 766 resource holder receives multiple allocations from the same source, 767 the set of resource certificates may be combined into a single 768 resource certificate, if both the issuer and the resource holder 769 agree. This is accomplished by consolidating the IP Address 770 Delegation and AS Identifier Delegation Extensions into a single 771 extension (of each type) in a new certificate. However, if the 772 certificates for these allocations contain different validity 773 intervals, creating a certificate that combines them might create 774 problems, and thus is NOT RECOMMENDED. 776 If a resource holder's allocations come from different sources, they 777 will be signed by different CAs, and cannot be combined. When a set 778 of resources is no longer allocated to a resource holder, any 779 certificates attesting to such an allocation MUST be revoked. A 780 resource holder SHOULD NOT use the same public key in multiple CA 781 certificates that are issued by the same or differing authorities, as 782 reuse of a key pair complicates path construction. Note that since 783 the subject's distinguished name is chosen by the issuer, a subject 784 who receives allocations from two sources generally will receive 785 certificates with different subject names. 787 7.2. ROA management 789 Whenever a holder of IP address space wants to authorize an AS to 790 originate routes for a prefix within his holdings, he MUST issue an 791 end-entity certificate containing that prefix in an IP Address 792 Delegation extension. He then uses the corresponding private key to 793 sign a ROA containing the designated prefix and the AS number for the 794 AS. The resource holder MAY include more than one prefix in the EE 795 certificate and corresponding ROA if desired. As a prerequisite, 796 then, any address space holder that issues ROAs for a prefix must 797 have a resource certificate for an allocation containing that prefix. 798 The standard procedure for issuing a ROA is as follows: 800 1. Create an end-entity certificate containing the prefix(es) to be 801 authorized in the ROA. 803 2. Construct the payload of the ROA, including the prefixes in the 804 end-entity certificate and the AS number to be authorized. 806 3. Sign the ROA using the private key corresponding to the end- 807 entity certificate (the ROA is comprised of the payload 808 encapsulated in a CMS signed message [7]). 810 4. Upload the end-entity certificate and the ROA to the repository 811 system. 813 The standard procedure for revoking a ROA is to revoke the 814 corresponding end-entity certificate by creating an appropriate CRL 815 and uploading it to the repository system. The revoked ROA and end- 816 entity certificate SHOULD BE removed from the repository system. 818 7.2.1. Single-homed subscribers (without provider independent addresses) 820 In BGP, a single-homed subscriber with provider allocated (non- 821 portable) address space does not need to explicitly authorize routes 822 to be originated for the prefix(es) it is using, since its ISP will 823 already advertise a more general prefix and route traffic for the 824 subscriber's prefix as an internal function. Since no routes are 825 originated specifically for prefixes held by these subscribers, no 826 ROAs need to be issued under their allocations; rather, the 827 subscriber's ISP will issue any necessary ROAs for its more general 828 prefixes under resource certificates from its own allocation. Thus, a 829 single-homed subscriber with an IP address allocation from his 830 service provider is not included in the RPKI, i.e., it does not 831 receive a CA certificate, nor issue EE certificates or ROAs. 833 7.2.2. Multi-homed subscribers (without provider independent addresses) 835 Here we consider a subscriber who receives IP address space from a 836 primary ISP (i.e., the IP addresses used by the subscriber are a 837 subset of ISP A's IP address space allocation) and receives redundant 838 upstream connectivity from the primary ISP, as well as one or more 839 secondary ISPs. The preferred option for such a multi-homed 840 subscribers is for the subscriber to obtain an AS number (from an RIR 841 or NIR) and run BGP with each of its upstream providers. In such a 842 case, there are two ways for ROA management to be handled. The first 843 is that the primary ISP issues a CA certificate to the subscriber, 844 and the subscriber issues a ROA to containing the subscriber's AS 845 number and the subscriber's IP address prefixes. The second 846 possibility is that the primary ISP does not issue a ROA to the 847 subscriber, and instead issues a ROA on the subscriber's behalf that 848 contains the subscriber's AS number and the subscriber's IP address 849 prefixes. 851 If the subscriber is unable or unwilling to obtain an AS number and 852 run BGP, the other option is that the multi-homed subscriber can 853 request that the primary ISP create a ROA for each secondary ISP that 854 authorizes the secondary ISP to originate routes to the subscriber's 855 prefixes. The primary ISP will also create a ROA containing its own 856 AS number and the subscriber's prefixes, as it is likely in such a 857 case that the primary ISP wishes to advertise precisely the 858 subscriber's prefixes and not an encompassing aggregate. Note that 859 this approach results in inconsistent origin AS numbers for the 860 subscribers prefixes which are considered undesirable on the public 861 Internet; thus this approach is NOT RECOMMENDED. 863 7.2.3. Provider-Independent Address Space 865 A resource holder is said to have provider-independent (portable) 866 address space if the resource holder received its allocation directly 867 from a RIR or NIR. Because the prefixes represented in such 868 allocations are not taken from an allocation held by an ISP, there is 869 no ISP that holds and advertises a more general prefix. A holder of a 870 portable IP address space allocation MUST authorize one or more ASes 871 to originate routes to these prefixes. Thus the resource holder MUST 872 generate one or more EE certificates and associated ROAs to enable 873 the AS(es) to originate routes for the prefix(es) in question. This 874 ROA is required because none of the ISP's existing ROAs authorize it 875 to originate routes to the subscriber's provider-idependent 876 allocation. 878 8. Security Considerations 880 The focus of this document is security; hence security considerations 881 permeate this specification. 883 The security mechanisms provided by and enabled by this architecture 884 depend on the integrity and availability of the infrastructure it 885 describes. The integrity of objects within the infrastructure is 886 ensured by appropriate controls on the repository system, as 887 described in Section 4.4. Likewise, because the repository system is 888 structured as a distributed database, it should be inherently 889 resistant to denial of service attacks; nonetheless, appropriate 890 precautions should also be taken, both through replication and backup 891 of the constituent databases and through the physical security of 892 database servers. 894 9. IANA Considerations 896 This document requests that the IANA issue RPKI Certificates for the 897 resources for which it is authoritative, i.e., reserved IPv4 898 addresses, IPv6 ULAs, and address space not yet allocated by IANA to 899 the RIRs. IANA SHOULD make available trust anchor material in the 900 format defined in [10] in support of these functions. 902 10. Acknowledgments 904 The architecture described in this draft is derived from the 905 collective ideas and work of a large group of individuals. This work 906 would not have been possible without the intellectual contributions 907 of George Michaelson, Robert Loomans, Sanjaya and Geoff Huston of 908 APNIC, Robert Kisteleki and Henk Uijterwaal of the RIPE NCC, Tim 909 Christensen and Cathy Murphy of ARIN, Rob Austein of ISC and Randy 910 Bush of IIJ. 912 Although we are indebted to everyone who has contributed to this 913 architecture, we would like to especially thank Rob Austein for the 914 concept of a manifest, Geoff Huston for the concept of managing 915 object validity through single-use EE certificate key pairs, and 916 Richard Barnes for help in preparing an early version of this 917 document. 919 11. References 921 11.1. Normative References 923 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 924 Levels", BCP 14, RFC 2119, March 1997. 926 [2] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 927 (BGP-4)", RFC 4271, January 2006 929 [3] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, 930 R., and W. Polk, "Internet X.509 Public Key Infrastructure 931 Certificate and Certificate Revocation List (CRL) Profile", RFC 932 5280, May 2008. 934 [4] Housley, R., "Cryptographic Message Syntax", RFC 3852, July 935 2004. 937 [5] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP 938 Addresses and AS Identifiers", RFC 3779, June 2004. 940 [6] Huston, G., Michaelson, G., and Loomans, R., "A Profile for 941 X.509 PKIX Resource Certificates", draft-ietf-sidr-res-certs- 942 16, February 2009. 944 [7] Lepinski, M., Kent, S., and Kong, D., "A Profile for Route 945 Origin Authorizations (ROA)", draft-ietf-sidr-roa-format-04, 946 November 2008. 948 [8] Austein, R., et al., "Manifests for the Resource Public Key 949 Infrastructure", draft-ietf-sidr-rpki-manifests-04, October 950 2008. 952 [9] Michaelson, G., Kent, S., and Huston, G., "A Profile for Trust 953 Anchor Material for the Resource Certificate PKI", draft-ietf- 954 sidr-ta-00, February 2009. 956 11.2. Informative References 958 [10] Huston, G., Michaelson, G., and Loomans, R., "A Profile for 959 Resource Certificate Repository Structure", draft-ietf-sidr- 960 repos-struct-01, October 2008. 962 [11] Kent, S., Lynn, C., and Seo, K., "Secure Border Gateway 963 Protocol (Secure-BGP)", IEEE Journal on Selected Areas in 964 Communications Vol. 18, No. 4, April 2000. 966 [12] White, R., "soBGP", May 2005, 969 [13] Tridgell, A., "rsync", April 2006, 970 972 [14] Huston, G., Michaelson, G., "Validation of Route Origination in 973 BGP using the Resource Certificate PKI", draft-ietf-sidr-roa- 974 validation-01, October 2008. 976 Authors' Addresses 978 Matt Lepinski 979 BBN Technologies 980 10 Moulton St. 981 Cambridge, MA 02138 983 Email: mlepinski@bbn.com 985 Stephen Kent 986 BBN Technologies 987 10 Moulton St. 988 Cambridge, MA 02138 990 Email: kent@bbn.com 992 Pre-5378 Material Disclaimer 994 This document may contain material from IETF Documents or IETF 995 Contributions published or made publicly available before November 996 10, 2008. The person(s) controlling the copyright in some of this 997 material may not have granted the IETF Trust the right to allow 998 modifications of such material outside the IETF Standards Process. 999 Without obtaining an adequate license from the person(s) controlling 1000 the copyright in such materials, this document may not be modified 1001 outside the IETF Standards Process, and derivative works of it may 1002 not be created outside the IETF Standards Process, except to format 1003 it for publication as an RFC or to translate it into languages other 1004 than English.