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Summary: 3 errors (**), 0 flaws (~~), 12 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Lepinski 3 Internet Draft BBN Technologies 4 Intended status: Informational S. Turner 5 Expires: January 4, 2015 IECA 6 July 4, 2014 8 An Overview of BGPSEC 9 draft-ietf-sidr-bgpsec-overview-05 11 Abstract 13 This document provides an overview of a security extension to the 14 Border Gateway Protocol (BGP) referred to as BGPSEC. BGPSEC improves 15 security for BGP routing. 17 Status of this Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that 24 other groups may also distribute working documents as Internet- 25 Drafts. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/ietf/1id-abstracts.txt 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html 38 This Internet-Draft will expire on November 8, 2012. 40 Copyright Notice 42 Copyright (c) 2012 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction...................................................2 58 2. Background.....................................................3 59 3. BGPSEC Operation...............................................4 60 3.1. Negotiation of BGPSEC.....................................4 61 3.2. Update signing and validation.............................5 62 4. Design and Deployment Considerations...........................6 63 4.1. Disclosure of topology information........................7 64 4.2. BGPSEC router assumptions.................................7 65 4.3. BGPSEC and consistency of externally visible data.........8 66 5. Security Considerations........................................8 67 6. IANA Considerations............................................8 68 7. References.....................................................9 69 7.1. Normative References......................................9 70 7.2. Informative References....................................9 72 1. Introduction 74 BGPSEC (Border Gateway Protocol Security) is an extension to the 75 Border Gateway Protocol (BGP) that provides improved security for BGP 76 routing [RFC 4271]. This document contains a brief overview of BGPSEC 77 and its envisioned usage. 79 A more detailed discussion of BGPSEC is provided in the following set 80 of documents: 82 . [I-D.sidr-bgpsec-threats]: 84 A threat model describing the security context in which BGPSEC 85 is intended to operate. 87 . [I-D.sidr-bgpsec-reqs]: 89 A set of requirements for BGP path security, which BGPSEC is 90 intended to satisfy. 92 . [I-D.sidr-bgpsec-protocol]: 94 A standards track document specifying the BGPSEC extension to 95 BGP. 97 . [I-D.sidr-bgpsec-ops]: 99 An informational document describing operational considerations. 101 . [I-D.turner-sidr-bgpsec-pki-profiles]: 103 A standards track document specifying a profile for X.509 104 certificates that bind keys used in BGPSEC to Autonomous System 105 numbers, as well as associated Certificate Revocation Lists 106 (CRLs), and certificate requests. 108 . [I-D.turner-sidr-bgpsec-algs] 110 A standards track document specifying suites of signature and 111 digest algorithms for use in BGPSEC. 113 In addition to this document set, some readers might be interested in 114 [I-D.sriram-bgpsec-design-choices], an informational document 115 describing the choices that were made the by the author team prior to 116 the publication of the -00 version of draft-ietf-sidr-bgpsec- 117 protocol. Discussion of design choices made since the publication of 118 the -00 can be found in the archives of the SIDR working group 119 mailing list. 121 2. Background 123 The motivation for developing BGPSEC is that BGP does not include 124 mechanisms that allow an Autonomous System (AS) to verify the 125 legitimacy and authenticity of BGP route advertisements (see for 126 example, [RFC 4272]). 128 The Resource Public Key Infrastructure (RPKI), described in 129 [RFC6480], provides a first step towards addressing the validation of 130 BGP routing data. RPKI resource certificates are issued to the 131 holders of AS number and IP address resources, providing a binding 132 between these resources and cryptographic keys that can be used to 133 verify digital signatures. Additionally, the RPKI architecture 134 specifies a digitally signed object, a Route Origination 135 Authorization (ROA), that allows holders of IP address resources to 136 authorize specific ASes to originate routes (in BGP) to these 137 resources. Data extracted from valid ROAs can be used by BGP speakers 138 to determine whether a received route was actually originated by an 139 AS authorized to originate that route (see [RFC6483] and [I-D.sidr- 140 origin-ops]). 142 By instituting a local policy that prefers routes with origins 143 validated using RPKI data (versus routes to the same prefix that 144 cannot be so validated) an AS can protect itself from certain mis- 145 origination attacks. However, use of RPKI data alone provides little 146 or no protection against a sophisticated attacker. Such an attacker 147 could, for example, conduct a route hijacking attack by appending an 148 authorized origin AS to an otherwise illegitimate AS path. (See [I- 149 D.sidr-bgpsec-threats] for a detailed discussion of the BGPSEC threat 150 model.) 152 BGPSEC extends the RPKI by adding an additional type of certificate, 153 referred to as a BGPSEC router certificate, that binds an AS number 154 to a public signature verification key, the corresponding private key 155 of which is held by one or more BGP speakers within this AS. Private 156 keys corresponding to public keys in such certificates can then be 157 used within BGPSEC to enable BGP speakers to sign on behalf of their 158 AS. The certificates thus allow a relying party to verify that a 159 BGPSEC signature was produced by a BGP speaker belonging to a given 160 AS. The goal of BGPSEC is to use such signatures to protect the AS 161 path data in BGP update messages so that a BGP speaker can assess the 162 validity of the AS Path in update messages that it receives. 164 3. BGPSEC Operation 166 The core of BGPSEC is a new optional (non-transitive) attribute, 167 called BGPSEC_Path_Signatures. This attribute consists of a sequence 168 of digital signatures, one for each AS in the AS Path of a BGPSEC 169 update message. (The use of this new attribute is formally specified 170 in [I-D.sidr-bgpsec-protocol].) A new signature is added to this 171 sequence each time an update message leaves an AS. The signature is 172 constructed so that any tampering with the AS path or Network Layer 173 Reachability Information (NLRI) in the BGPSEC update message can be 174 detected by the recipient of the message. 176 3.1. Negotiation of BGPSEC 178 The use of BGPSEC is negotiated using BGP capability advertisements 179 [RFC 5492]. Upon opening a BGP session with a peer, BGP speakers who 180 support (and wish to use) BGPSEC include a newly-defined capability 181 in the OPEN message. 183 The use of BGPSEC is negotiated separately for each address family. 184 This means that a BGP speaker could, for example, elect to use BGPSEC 185 for IPv6, but not for IPv4 (or vice versa). Additionally, the use of 186 BGPSEC is negotiated separately in the send and receive directions. 187 This means that a BGP speaker could, for example, indicate support 188 for sending BGPSEC update messages but require that messages it 189 receives be traditional (non-BGPSEC) update message. (To see why such 190 a feature might be useful, see Section 4.2.) 191 If the use of BGPSEC is negotiated in a BGP session (in a given 192 direction, for a given address family) then both BGPSEC update 193 messages (ones that contain the BGPSEC_Path_Signature attribute) and 194 traditional BGP update messages (that do not contain this attribute) 195 can be sent within the session. 197 If a BGPSEC-capable BGP speaker finds that its peer does not support 198 receiving BGPSEC update messages, then the BGP speaker must remove 199 existing BGPSEC_Path_Signatures attribute from any update messages it 200 sends to this peer. 202 3.2. Update signing and validation 204 When a BGP speaker originates a BGPSEC update message, it creates a 205 BGPSEC_Path_Signatures attribute containing a single signature. The 206 signature protects the Network Layer Reachability Information (NLRI), 207 the AS number of the originating AS, and the AS number of the peer AS 208 to whom the update message is being sent. Note that the NLRI in a 209 BGPSEC update message is restricted to contain only a single prefix. 211 When a BGP speaker receives a BGPSEC update message and wishes to 212 propagate the route advertisement contained in the update to an 213 external peer, it adds a new signature to the BGPSEC_Path_Signatures 214 attribute. This signature protects everything protected by the 215 previous signature, plus the AS number of the new peer to whom the 216 update message is being sent. 218 Each BGP speaker also adds a reference, called a Subject Key 219 Identifier (SKI), to its BGPSEC Router certificate. The SKI is used 220 by a recipient to select the public key (and associated router 221 certificate data) needed for validation. 223 As an example, consider the following case in which an advertisement 224 for 192.0.2/24 is originated by AS 1, which sends the route to AS 2, 225 which sends it to AS 3, which sends it to AS 4. When AS 4 receives a 226 BGPSEC update message for this route, it will contain the following 227 data: 229 . NLRI : 192.0.2/24 231 . AS Path : 3 2 1 233 . BGPSEC_Path_Signatures Attribute with 3 signatures : 234 o Signature from AS 1 protecting 236 192.0.2/24, AS 1 and AS 2 238 o Signature from AS 2 protecting 239 Everything AS 1's signature protected, and AS 3 241 o Signature from AS 3 protecting 243 Everything AS 2's signature protected, and AS 4 245 When a BGPSEC update message is received by a BGP speaker, the BGP 246 speaker can validate the message as follows. For each signature, the 247 BGP speaker first needs to determine if there is a valid RPKI Router 248 certificate matching the SKI and containing the appropriate AS 249 number. (This would typically be done by looking up the SKI in a 250 cache of data extracted from valid RPKI objects. A cache allows 251 certificate validation to be handled via an asynchronous process, 252 which might execute on another device.) 254 The BGP speaker then verifies the signature using the public key from 255 this BGPSEC router certificate. If all the signatures can be verified 256 in this fashion, the BGP speaker is assured that the update message 257 it received actually came via the AS path specified in the update 258 message. Finally, the BGP speaker can check whether there exists a 259 valid ROA in the RPKI linking the origin AS to the prefix in the 260 NLRI. If such a valid ROA exists the BGP speaker is further assured 261 that the AS at the beginning of the validated path was authorized to 262 originate routes to the given prefix. 264 In the above example, upon receiving the BGPSEC update message, a BGP 265 speaker for AS 4 would first check to make sure that there is a valid 266 ROA authorizing AS 1 to originate advertisements for 192.0.2/24. It 267 would then look at the SKI for the first signature and see if this 268 corresponds to a valid BGPSEC Router certificate for AS 1. Next, it 269 would then verify the first signature using the key found in this 270 valid certificate. Finally, it would repeat this process for the 271 second and third signatures, checking to see that there are valid 272 BGPSEC router certificates for AS 2 and AS 3 (respectively) and that 273 the signatures can be verified with the keys found in these 274 certificates. 276 4. Design and Deployment Considerations 278 In this section we provide a brief overview of several additional topics that 279 commonly arise in the discussion of BGPSEC. 281 4.1. Disclosure of topology information 283 A key requirement in the design of BGPSEC was that BGPSEC not 284 disclose any new information about BGP peering topology. Since many 285 ISPs feel peering topology data is proprietary, further disclosure of 286 it would inhibit BGPSEC adoption. 288 In particular, the topology information that can be inferred from 289 BGPSEC update messages is exactly the same as that which can be 290 inferred from equivalent (non-BGPSEC) BGP update messages. 292 4.2. BGPSEC router assumptions 294 In order to achieve its security goals, BGPSEC assumes additional 295 capabilities in routers. In particular, BGPSEC involves adding 296 digital signatures to BGP update messages, which will significantly 297 increase the size of these messages. Therefore, an AS that wishes to 298 receive BGPSEC update messages will require additional memory in its 299 routers to store (e.g., in ADJ RIBs) the data conveyed in these large 300 update messages. Additionally, the design of BGPSEC assumes that an 301 AS that elects to receive BGPSEC update messages will do some 302 cryptographic signature verification at its edge router. This 303 verification will likely require additional capability in these edge 304 routers. 306 Additionally, BGPSEC requires that all BGPSEC speakers will support 307 4-byte AS Numbers [RFC4893]. This is because the co-existence 308 strategy for 4-byte AS numbers and legacy 2-byte AS speakers that 309 gives special meaning to AS 23456 is incompatible with the security 310 the security properties that BGPSEC seeks to provide. 312 For this initial version of BGPSEC, optimizations to minimize the 313 size of BGPSEC updates or the processing required in edge routers 314 have not been considered. Such optimizations may be considered in the 315 future. 317 Note also that the design of BGPSEC allows an AS to send BGPSEC 318 update messages (thus obtaining protection for routes it originates) 319 without receiving BGPSEC update messages. An AS that only sends, and 320 does not receive, BGPSEC update messages will require much less 321 capability in its edge routers to deploy BGPSEC. In particular, a 322 router that only sends BGPSEC update messages does not need 323 additional memory to store large updates and requires only minimal 324 cryptographic capability (as generating one signature per outgoing 325 update requires less computation than verifying multiple signatures 326 on each incoming update message). See [I-D.sidr-bgpsec-ops] for 327 further discussion related to Edge ASes that do not provide transit. 329 4.3. BGPSEC and consistency of externally visible data 331 Finally note that, by design, BGPSEC prevents parties that propagate 332 route advertisements from including inconsistent or erroneous 333 information within the AS-Path (without detection). In particular, 334 this means that any deployed scenarios in which a BGP speaker 335 constructs such an inconsistent or erroneous AS Path attribute will 336 break when BGPSEC is used. 338 For example, when BGPSEC is not used, it is possible for a single 339 autonomous system to have one peering session where it identifies 340 itself as AS 111 and a second peering session where it identifies 341 itself as AS 222. In such a case, it might receive route 342 advertisements from the first peering session (as AS 111) and then 343 add AS 222 (but not AS 111) to the AS-Path and propagate them within 344 the second peering session. 346 Such behavior may very well be innocent and performed with the 347 consent of the legitimate holder of both AS 111 and 222. However, it 348 is indistinguishable from the following man-in-the-middle attack 349 performed by a malicious AS 222. First, the malicious AS 222 350 impersonates AS 111 in the first peering session (essentially 351 stealing a route advertisement intended for AS 111). The malicious AS 352 222 then inserts itself into the AS path and propagates the update to 353 its peers. 355 Therefore, when BGPSEC is used, such an autonomous system would 356 either need to assert a consistent AS number in all external peering 357 sessions, or else it would need to add both AS 111 and AS 222 to the 358 AS-Path (along with appropriate signatures) for route advertisements 359 that it receives from the first peering session and propagates within 360 the second peering session. 362 5. Security Considerations 364 This document provides an overview of BPSEC; it does not define the 365 BGPSEC extension to BGP. The BGPSEC extension is defined in [I- 366 D.sidr-bgpsec-protocol]. The threat model for the BGPSEC is 367 described in [I-D.sidr-bgpsec-threats]. 369 6. IANA Considerations 371 None. 373 7.1. Normative References 375 [RFC4271] Rekhter, Y., Li, T., and S. Hares, Eds., "A Border Gateway 376 Protocol 4 (BGP-4)", RFC 4271, January 2006. 378 [RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS 379 Numbers", RFC 4893, May 2007. 381 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 382 with BGP-4", RFC 5492, February 2009. 384 [RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support 385 Secure Internet Routing", February 2012. 387 [RFC6483] Huston, G., and G. Michaelson, "Validation of Route 388 Origination using the Resource Certificate PKI and ROAs", February 389 2012. 391 [I-D.sidr-origin-ops] Bush, R., "RPKI-Based Origin Validation 392 Operation", draft-ietf-sidr-origin-ops, work-in-progress. 394 [I-D.sidr-bgpsec-threats] Kent, S., and A. Chi, "Threat Model for BGP 395 Path Security", draft-ietf-sidr-bgpsec-threats, work-in-progress. 397 [I-D.sidr-bgpsec-protocol] Lepinski, M., Ed., "BPSEC Protocol 398 Specification", draft-ietf-sidr-bgpsec-protocol, work-in-progress. 400 [I-D.sidr-bgpsec-ops] Bush, R., "BGPSEC Operational Considerations", 401 draft-ietf-sidr-bgpsec-ops, work-in-progress. 403 [I-D.sidr-bgpsec-algs] Turner, S., "BGP Algorithms, Key Formats, & 404 Signature Formats", draft-ietf-sidr-bgpsec-algs, work-in-progress. 406 [I-D.sidr-bgpsec-pki-profiles] Reynolds, M. and S. Turner, S., "A 407 Profile for BGPSEC Router Certificates, Certificate Revocation Lists, 408 and Certification Requests", draft-sidr-bgpsec-pki-profiles, work-in- 409 progress. 411 7.2. Informative References 413 [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", RFC 414 4272, January 2006 416 [I-D.sriram-bgpsec-design-choices] Sriram, K., "BGPSEC Design Choices 417 and Summary of Supporting Discussions", draft-sriram-bgpsec-design- 418 choices, work-in-progress. 420 [I-D.sidr-bgpsec-reqs] Bellovin, S., R. Bush, and D. Ward, "Security 421 Requirements for BGP Path Validation", draft-ietf-sidr-bgpsec-reqs, 422 work-in-progress. 424 Author's' Addresses 426 Matt Lepinski 427 BBN Technologies 428 10 Moulton Street 429 Cambridge MA 02138 431 Email: mlepinski.ietf@gmail.com 433 Sean Turner 434 IECA, Inc. 435 3057 Nutley Street, Suite 106 436 Fairfax, VA 22031 438 Email: turners@ieca.com