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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group M. Lepinski 2 Internet Draft BBN Technologies 3 Intended status: Informational S. Turner 4 Expires: September 7, 2011 IECA 5 March 7, 2011 7 An Overview of BGPSEC 8 draft-lepinski-bgpsec-overview-00.txt 10 Abstract 12 This document provides an overview of a security extension to the 13 Border Gateway Protocol (BGP) referred to as BGPSEC. BGPSEC improves 14 security for BGP routing. 16 Status of this Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF), its areas, and its working groups. Note that 23 other groups may also distribute working documents as Internet- 24 Drafts. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 The list of current Internet-Drafts can be accessed at 32 http://www.ietf.org/ietf/1id-abstracts.txt 34 The list of Internet-Draft Shadow Directories can be accessed at 35 http://www.ietf.org/shadow.html 37 This Internet-Draft will expire on October 7, 2011. 39 Copyright Notice 41 Copyright (c) 2011 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. 51 Table of Contents 53 1. Introduction...................................................2 54 2. Background.....................................................3 55 3. BGPSEC Operation...............................................4 56 3.1. Negotiation of BGPSEC.....................................4 57 3.2. Update signing and validation.............................5 58 4. Design and Deployment Considerations...........................6 59 4.1. Disclosure of topology information........................7 60 4.2. BGPSEC router assumptions.................................7 61 4.3. BGPSEC and consistency of externally visible data.........7 62 5. Security Considerations........................................8 63 6. IANA Considerations............................................8 64 7. References.....................................................8 65 7.1. Normative References......................................8 66 7.2. Informative References....................................9 68 1. Introduction 70 BGPSEC (Border Gateway Protocol Security) is an extension to the 71 Border Gateway Protocol (BGP) that provides improved security for BGP 72 routing [RFC 4271]. 74 A comprehensive discussion of BGPSEC is provided in the following set 75 of documents: 77 . [I-D.kent-bgpsec-threats]: 79 A threat model describing the security context in which BGPSEC 80 is intended to operate. 82 . [I-D.lepinski-bgpsec-protocol]: 84 A standards track document specifying the BGPSEC extension to 85 BGP. 87 . [I-D.ymbk-bgpsec-ops]: 89 An informational document describing operational considerations 90 for BGPSEC deployment. 92 . Certificate Profile Document (TBD) 94 A standards track document specifying a profile for X.509 95 certificates that bind keys used in BGPSEC to Autonomous System 96 numbers as well as Certificate Revocation Lists (CRLs), 97 certificate requests. 99 . Algorithms Document (TBD) 101 A standards track document specifying suites of signature and 102 digest algorithms for use in BGPSEC. 104 . Design Choices Document (TBD) 106 An informational document describing the choices that were made 107 in designing BGPSEC and the reasoning behind these choices. 109 The remainder of this document contains a brief overview of BGPSEC 110 and envisioned usage. 112 2. Background 114 The motivation for developing BGPSEC is that BGP does not include 115 mechanisms that allow an Autonomous System (AS) to verify the 116 legitimacy and authenticity of BGP route advertisements (see for 117 example, [RFC 4272]). 119 The Resource Public Key Infrastructure (RPKI), described in [I- 120 D.sidr-arch], provides a first step towards addressing the validation 121 of BGP routing data. RPKI resource certificates are issued to the 122 holders of AS number and IP address resources, providing a binding 123 between these resources and cryptographic keys that can be used to 124 verify digital signatures. Additionally, the RPKI architecture 125 specifies a digitally signed object, a Route Origination 126 Authorization (ROA), that allows holders of IP address resources to 127 authorize specific ASes to originate routes (in BGP) to these 128 resources. Data extracted from valid ROAs can be used by BGP speakers 129 to determine whether a received route was originated by an AS 130 authorized to originate that route (see [I-D.sidr-roa-validation] and 131 [I-D.sidr-origin-ops]). 133 By instituting a local policy that prefers routes with origins 134 validated using RPKI data (versus routes to the same prefix that 135 cannot be so validated) an AS can protect itself from certain mis- 136 origination attacks. For example, if a BGP speaker accidently (due to 137 misconfiguration) originates routes to the wrong prefixes, ASes 138 utilizing RPKI data could detect this error and decline to select 139 these mis-originated routes. However, use of RPKI data alone provides 140 little or no protection against a sophisticated attacker. Such an 141 attacker could, for example, conduct a route hijacking attack by 142 appending an authorized origin AS to an otherwise illegitimate AS 143 Path. (See [I-D.kent-security-threats] for a detailed discussion of 144 the BGPSEC threat model.) 146 BGPSEC extends the RPKI by adding an additional type of certificate, 147 referred to as a BGPSEC router certificate, that binds an AS number 148 to a public signature verification key, the corresponding private key 149 of which is held by one or more BGP speakers within this AS. Private 150 keys corresponding to public keys in such certificates can then be 151 used within BGPSEC to enable BGP speakers to sign on behalf of their 152 AS. The certificates thus allow a relying party to verify that a 153 BGPSEC signature was produced by a BGP speaker belonging to a given 154 AS. The goal of BGPSEC is to use signatures to protect the AS Path 155 attribute of BGP update messages so that a BGP speaker can assess the 156 validity of the AS Path in update messages that it receives. 158 3. BGPSEC Operation 160 The core of BGPSEC is a new optional (non-transitive) attribute, 161 called BGPSEC_Path_Signatures. This attribute consists of a sequence 162 of digital signatures, one for each AS in the AS Path of a BGPSEC 163 update message. (The use of this new attribute is formally specified 164 in [I-D.lepinski-bgpsec-protocol].) A new signature is added to this 165 sequence each time an update message leaves an AS. The signature is 166 constructed so that any tampering with the AS path or Network Layer 167 Reachability Information (NLRI) in the BGPSEC update message will 168 result in the recipient being able to detect that the update is 169 invalid. 171 3.1. Negotiation of BGPSEC 173 The use of BGPSEC is negotiated using BGP capability advertisements 174 [RFC 5492]. Upon opening a BGP session with a peer, BGP speakers who 175 support (and wish to use) BGPSEC include a newly-defined capability 176 in the OPEN message. 178 The use of BGPSEC is negotiated separately for each address family. 179 This means that a BGP speaker could, for example, elect to use BGPSEC 180 for IPv6, but not for IPv4 (or vice versa). Additionally, the use of 181 BGPSEC is negotiated separately in the send and receive directions. 182 This means that a BGP speaker could, for example, indicate support 183 for sending BGPSEC update messages but require that messages it 184 receives be traditional (non-BGPSEC) update message. (To see why such 185 a feature might be useful, see Section 4.2.) 186 If the use of BGPSEC is negotiated in a BGP session (in a given 187 direction, for a given address family) then both BGPSEC update 188 messages (ones that contain the BGPSEC_Path_Signature attribute) and 189 traditional BGP update messages (that do not contain this attribute) 190 can be sent within the session. 192 If a BGPSEC-capable BGP speaker finds that its peer does not support 193 receiving BGPSEC update messages, then the BGP speaker must remove 194 existing BGPSEC_Path_Signatures attribute from any update messages it 195 sends to this peer. 197 3.2. Update signing and validation 199 When a BGP speaker originates a BGPSEC update message, it creates a 200 BGPSEC_Path_Signatures attribute containing a single signature. The 201 signature protects the Network Layer Reachability Information (NLRI), 202 the AS number of the originating AS, the AS number of the peer AS to 203 whom the update message is being sent, and a few other pieces of data 204 necessary for security guarantees. Note that the NLRI in a BGPSEC 205 update message is restricted to contain only a single prefix. 207 When a BGP speaker receives a BGPSEC update message and wishes to 208 propagate the route advertisement contained in the update to an 209 external peer, it adds a new signature to the BGPSEC_Path_Signatures 210 attribute. This signature protects everything protected by the 211 previous signature, plus the AS number of the new peer to whom the 212 update message is being sent. 214 Each BGP speaker also adds a reference, called a Subject Key 215 Identifier (SKI), to its BGPSEC Router certificate. The SKI is used 216 by a recipient to select the public key (and selected router 217 certificate data) needed for validation. 219 As an example, consider the following case in which an advertisement 220 for 192.0.2/24 is originated by AS 1, which sends the route to AS 2, 221 which sends it to AS 3, which sends it to AS 4. When AS 4 receives a 222 BGPSEC update message for this route, it will contain the following 223 data: 225 . NLRI : 192.0.2/24 227 . AS_Path : 3 2 1 229 . BGPSEC_Path_Signatures Attribute with 3 signatures : 231 o Signature from AS 1 protecting 232 192.0.2/24, AS 1 and AS 2 234 o Signature from AS 2 protecting 236 Everything AS 1's signature protected, and AS 3 238 o Signature from AS 3 protecting 240 Everything AS 2's signature protected, and AS 4 242 When a BGPSEC update message is received by a BGP speaker, the BGP 243 speaker can validate the message as follows. For each signature, the 244 BGP speaker first needs to determine if there is a valid RPKI Router 245 certificate matching the SKI and containing the appropriate AS 246 number. (This would typically be done by looking up the SKI in a 247 cache of data extracted from valid RPKI objects. A cache allows 248 certificate validation to be handled via an asynchronous process, 249 which might execute on another device.) 251 The BGP speaker then verifies the signature using the public key from 252 this BGPSEC router certificate. If all the signatures can be verified 253 in this fashion, the BGP speaker is assured that the update message 254 it received actually came via the path specified in the AS_Path 255 attribute. Finally, the BGP speaker can check whether there exists a 256 valid ROA in the RPKI linking the origin AS to the prefix in the 257 NLRI. If such a valid ROA exists the BGP speaker is further assured 258 that the AS at the beginning of the validated path was authorized to 259 originate routes to the given prefix. 261 In the above example, upon receiving the BGPSEC update message, a BGP 262 speaker for AS 4 would first check to make sure that there is a valid 263 ROA authorizing AS 1 to originate advertisements for 192.0.2/24. It 264 would then look at the SKI for the first signature and see if this 265 corresponds to a valid BGPSEC Router certificate for AS 1. Next, it 266 would then verify the first signature using the key found in this 267 valid certificate. Finally, it would repeat this process for the 268 second and third signatures, checking to see that there are valid 269 BGPSEC router certificates for AS 2 and AS 3 (respectively) and that 270 the signatures can be verified with the keys found in these 271 certificates. 273 4. Design and Deployment Considerations 275 In this section we briefly discuss several additional topics that 276 commonly arise in the discussion of BGPSEC. 278 4.1. Disclosure of topology information 280 A key requirement in the design of BGPSEC was that BGPSEC not 281 disclose any new information about BGP peering topology. Since many 282 ISPs feel peering topology data is proprietary, further disclosure of 283 it would inhibit BGPSEC adoption. 285 In particular, the topology information that can be inferred from 286 BGPSEC update messages is exactly the same as that which can be 287 inferred from equivalent (non-BGPSEC) BGP update messages. 289 4.2. BGPSEC router assumptions 291 In order to achieve its security goals, BGPSEC assumes additional 292 capabilities in routers. In particular, BGPSEC involves adding 293 digital signatures to BGP update messages, which will significantly 294 increase the size of these messages. Therefore, an AS that wishes to 295 receive BGPSEC update messages will require additional memory in its 296 routers to store (e.g., in ADJ RIBs) the data conveyed in these large 297 update messages. Additionally, the design of BGPSEC assumes that an 298 AS that elects to receive BGPSEC update messages will do some 299 cryptographic signature verification at its edge router. This 300 verification will likely require additional capability in these edge 301 routers. 303 For this initial version of BGPSEC, optimizations to minimize the 304 size of BGPSEC updates or the processing required in edge routers 305 were NOT considered. Such optimizations may be considered in the 306 future. 308 Note also that the design of BGPSEC allows an AS to send BGPSEC 309 update messages (thus obtaining protection for routes it originates) 310 without receiving BGPSEC update messages. An AS that only sends, and 311 does not receive, BGPSEC update messages will require much less 312 capability in its edge routers to deploy BGPSEC. In particular, a 313 router that only sends BGPSEC update messages does not need 314 additional memory to store large updates and requires only minimal 315 cryptographic capability (as generating one signature per outgoing 316 update requires less computation than verifying multiple signatures 317 on each incoming update message). See [I-D.ymbk-bgpsec-ops] for 318 further discussion related to Edge ASes that do not provide transit.) 320 4.3. BGPSEC and consistency of externally visible data 322 Finally note that, by design, BGPSEC prevents parties that propagate 323 route advertisements from including inconsistent or erroneous 324 information within the AS-Path (without detection). In particular, 325 this means that any deployed scenarios in which a BGP speaker 326 constructs such an inconsistent or erroneous AS Path attribute will 327 break when BGPSEC is used. 329 For example, when BGPSEC is not used, it is possible for a single 330 autonomous system to have one peering session where it identifies 331 itself as AS 111 and a second peering session where it identifies 332 itself as AS 222. In such a case, it might receive route 333 advertisements from the first peering session (as AS 111) and then 334 add AS 222 (but not AS 111) to the AS-Path and propagate them within 335 the second peering session. 337 Such behavior may very well be innocent and performed with the 338 consent of the legitimate holder of both AS 111 and 222. However, it 339 is indistinguishable from the following man-in-the-middle attack 340 performed by a malicious AS 222. First, the malicious AS 222 341 impersonates AS 111 in the first peering session (essentially 342 stealing a route advertisement intended for AS 111). The malicious AS 343 222 then inserts itself into the AS path and propagates the update to 344 its peers. 346 Therefore, when BGPSEC is used, such an autonomous system would 347 either need to assert a consistent AS number in all external peering 348 sessions, or else it would need to add both AS 111 and AS 222 to the 349 AS-Path (along with appropriate signatures) for route advertisements 350 that it receives from the first peering session and propagates within 351 the second peering session. 353 5. Security Considerations 355 This document provides an overview of BPSEC; it does not define the 356 BGPSEC extension to BGP. The BGPSEC extension is defined in [I- 357 D.lepinski-bgpsec-protocol]. The threat model for the BGPSEC is 358 described in [I-D.kent-bgpsec-threats]. 360 6. IANA Considerations 362 None. 364 7. References 366 7.1. Normative References 368 [RFC4271] Rekhter, Y., Li, T., and S. Hares, Eds., "A Border Gateway 369 Protocol 4 (BGP-4)", RFC 4271, January 2006. 371 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 372 with BGP-4", RFC 5492, February 2009. 374 [I-D.sidr-arch] Lepinski, M. and S. Kent, "An Infrastructure to 375 Support Secure Internet Routing", draft-ietf-sidr-arch, work-in- 376 progress. 378 [I-D.sidr-roa-validation] Huston, G., and Michaelson, G., "Validation 379 of Route Origination using the Resource Certificate PKI and ROAs", 380 draft-ietf-sidr-roa-validation, work-in-progress. 382 [I-D.sidr-origin-ops] Bush, R., "RPKI-Based Origin Validation 383 Operation", draft-ietf-sidr-origin-ops, work-in-progress. 385 [I-D.kent-bgpsec-threats] Kent, S., "Threat Model for BGP Path 386 Security", draft-kent-bgpsec-threats, work-in-progress. 388 [I-D.lepinski-bgpsec-protocol] Lepinski, M., Ed., "BPSEC Protocol 389 Specification", draft-lepinski-bgpsec-protocol, work-in-progress. 391 [I-D.ymbk-bgpsec-ops] Bush, R., "BGPSEC Operational Considerations", 392 draft-ymbk-bgpsec-ops, work-in-progress. 394 7.2. Informative References 396 [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", RFC 397 4272, January 2006 399 Authors' Addresses 401 Matt Lepinski 402 BBN Technologies 403 10 Moulton Street 404 Cambridge MA 02138 406 Email: mlepinski@bbn.com 408 Sean Turner 409 IECA, Inc. 410 3057 Nutley Street, Suite 106 411 Fairfax, VA 22031 413 Email: turners@ieca.com