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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: December 14, 2011 IECA 5 June 15, 2011 7 An Overview of BGPSEC 8 draft-ietf-sidr-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 December 15, 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. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction...................................................2 57 2. Background.....................................................3 58 3. BGPSEC Operation...............................................4 59 3.1. Negotiation of BGPSEC.....................................4 60 3.2. Update signing and validation.............................5 61 4. Design and Deployment Considerations...........................7 62 4.1. Disclosure of topology information........................7 63 4.2. BGPSEC router assumptions.................................7 64 4.3. BGPSEC and consistency of externally visible data.........8 65 5. Security Considerations........................................8 66 6. IANA Considerations............................................8 67 7. References.....................................................9 68 7.1. Normative References......................................9 69 7.2. Informative References....................................9 71 1. Introduction 73 BGPSEC (Border Gateway Protocol Security) is an extension to the 74 Border Gateway Protocol (BGP) that provides improved security for BGP 75 routing [RFC 4271]. 77 A comprehensive discussion of BGPSEC is provided in the following set 78 of documents: 80 . [I-D.kent-bgpsec-threats]: 82 A threat model describing the security context in which BGPSEC 83 is intended to operate. 85 . [I-D.sidr-bgpsec-protocol]: 87 A standards track document specifying the BGPSEC extension to 88 BGP. 90 . [I-D.ymbk-bgpsec-ops]: 92 An informational document describing operational considerations 93 for BGPSEC deployment. 95 . Certificate Profile Document (TBD) 97 A standards track document specifying a profile for X.509 98 certificates that bind keys used in BGPSEC to Autonomous System 99 numbers as well as Certificate Revocation Lists (CRLs), 100 certificate requests. 102 . Algorithms Document (TBD) 104 A standards track document specifying suites of signature and 105 digest algorithms for use in BGPSEC. 107 . Design Choices Document (TBD) 109 An informational document describing the choices that were made 110 in designing BGPSEC and the reasoning behind these choices. 112 The remainder of this document contains a brief overview of BGPSEC 113 and envisioned usage. 115 2. Background 117 The motivation for developing BGPSEC is that BGP does not include 118 mechanisms that allow an Autonomous System (AS) to verify the 119 legitimacy and authenticity of BGP route advertisements (see for 120 example, [RFC 4272]). 122 The Resource Public Key Infrastructure (RPKI), described in [I- 123 D.sidr-arch], provides a first step towards addressing the validation 124 of BGP routing data. RPKI resource certificates are issued to the 125 holders of AS number and IP address resources, providing a binding 126 between these resources and cryptographic keys that can be used to 127 verify digital signatures. Additionally, the RPKI architecture 128 specifies a digitally signed object, a Route Origination 129 Authorization (ROA), that allows holders of IP address resources to 130 authorize specific ASes to originate routes (in BGP) to these 131 resources. Data extracted from valid ROAs can be used by BGP speakers 132 to determine whether a received route was originated by an AS 133 authorized to originate that route (see [I-D.sidr-roa-validation] and 134 [I-D.sidr-origin-ops]). 136 By instituting a local policy that prefers routes with origins 137 validated using RPKI data (versus routes to the same prefix that 138 cannot be so validated) an AS can protect itself from certain mis- 139 origination attacks. For example, if a BGP speaker accidently (due to 140 misconfiguration) originates routes to the wrong prefixes, ASes 141 utilizing RPKI data could detect this error and decline to select 142 these mis-originated routes. However, use of RPKI data alone provides 143 little or no protection against a sophisticated attacker. Such an 144 attacker could, for example, conduct a route hijacking attack by 145 appending an authorized origin AS to an otherwise illegitimate AS 146 Path. (See [I-D.kent-security-threats] for a detailed discussion of 147 the BGPSEC threat model.) 149 BGPSEC extends the RPKI by adding an additional type of certificate, 150 referred to as a BGPSEC router certificate, that binds an AS number 151 to a public signature verification key, the corresponding private key 152 of which is held by one or more BGP speakers within this AS. Private 153 keys corresponding to public keys in such certificates can then be 154 used within BGPSEC to enable BGP speakers to sign on behalf of their 155 AS. The certificates thus allow a relying party to verify that a 156 BGPSEC signature was produced by a BGP speaker belonging to a given 157 AS. The goal of BGPSEC is to use signatures to protect the AS Path 158 attribute of BGP update messages so that a BGP speaker can assess the 159 validity of the AS Path in update messages that it receives. 161 3. BGPSEC Operation 163 The core of BGPSEC is a new optional (non-transitive) attribute, 164 called BGPSEC_Path_Signatures. This attribute consists of a sequence 165 of digital signatures, one for each AS in the AS Path of a BGPSEC 166 update message. (The use of this new attribute is formally specified 167 in [I-D.lepinski-bgpsec-protocol].) A new signature is added to this 168 sequence each time an update message leaves an AS. The signature is 169 constructed so that any tampering with the AS path or Network Layer 170 Reachability Information (NLRI) in the BGPSEC update message will 171 result in the recipient being able to detect that the update is 172 invalid. 174 3.1. Negotiation of BGPSEC 176 The use of BGPSEC is negotiated using BGP capability advertisements 177 [RFC 5492]. Upon opening a BGP session with a peer, BGP speakers who 178 support (and wish to use) BGPSEC include a newly-defined capability 179 in the OPEN message. 181 The use of BGPSEC is negotiated separately for each address family. 182 This means that a BGP speaker could, for example, elect to use BGPSEC 183 for IPv6, but not for IPv4 (or vice versa). Additionally, the use of 184 BGPSEC is negotiated separately in the send and receive directions. 185 This means that a BGP speaker could, for example, indicate support 186 for sending BGPSEC update messages but require that messages it 187 receives be traditional (non-BGPSEC) update message. (To see why such 188 a feature might be useful, see Section 4.2.) 190 If the use of BGPSEC is negotiated in a BGP session (in a given 191 direction, for a given address family) then both BGPSEC update 192 messages (ones that contain the BGPSEC_Path_Signature attribute) and 193 traditional BGP update messages (that do not contain this attribute) 194 can be sent within the session. 196 If a BGPSEC-capable BGP speaker finds that its peer does not support 197 receiving BGPSEC update messages, then the BGP speaker must remove 198 existing BGPSEC_Path_Signatures attribute from any update messages it 199 sends to this peer. 201 3.2. Update signing and validation 203 When a BGP speaker originates a BGPSEC update message, it creates a 204 BGPSEC_Path_Signatures attribute containing a single signature. The 205 signature protects the Network Layer Reachability Information (NLRI), 206 the AS number of the originating AS, the AS number of the peer AS to 207 whom the update message is being sent, and a few other pieces of data 208 necessary for security guarantees. Note that the NLRI in a BGPSEC 209 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 selected 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 1 232 . 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 240 Everything AS 1's signature protected, and AS 3 242 o Signature from AS 3 protecting 244 Everything AS 2's signature protected, and AS 4 246 When a BGPSEC update message is received by a BGP speaker, the BGP 247 speaker can validate the message as follows. For each signature, the 248 BGP speaker first needs to determine if there is a valid RPKI Router 249 certificate matching the SKI and containing the appropriate AS 250 number. (This would typically be done by looking up the SKI in a 251 cache of data extracted from valid RPKI objects. A cache allows 252 certificate validation to be handled via an asynchronous process, 253 which might execute on another device.) 255 The BGP speaker then verifies the signature using the public key from 256 this BGPSEC router certificate. If all the signatures can be verified 257 in this fashion, the BGP speaker is assured that the update message 258 it received actually came via the path specified in the AS_Path 259 attribute. Finally, the BGP speaker can check whether there exists a 260 valid ROA in the RPKI linking the origin AS to the prefix in the 261 NLRI. If such a valid ROA exists the BGP speaker is further assured 262 that the AS at the beginning of the validated path was authorized to 263 originate routes to the given prefix. 265 In the above example, upon receiving the BGPSEC update message, a BGP 266 speaker for AS 4 would first check to make sure that there is a valid 267 ROA authorizing AS 1 to originate advertisements for 192.0.2/24. It 268 would then look at the SKI for the first signature and see if this 269 corresponds to a valid BGPSEC Router certificate for AS 1. Next, it 270 would then verify the first signature using the key found in this 271 valid certificate. Finally, it would repeat this process for the 272 second and third signatures, checking to see that there are valid 273 BGPSEC router certificates for AS 2 and AS 3 (respectively) and that 274 the signatures can be verified with the keys found in these 275 certificates. 277 4. Design and Deployment Considerations 279 In this section we briefly discuss several additional topics that 280 commonly arise in the discussion of BGPSEC. 282 4.1. Disclosure of topology information 284 A key requirement in the design of BGPSEC was that BGPSEC not 285 disclose any new information about BGP peering topology. Since many 286 ISPs feel peering topology data is proprietary, further disclosure of 287 it would inhibit BGPSEC adoption. 289 In particular, the topology information that can be inferred from 290 BGPSEC update messages is exactly the same as that which can be 291 inferred from equivalent (non-BGPSEC) BGP update messages. 293 4.2. BGPSEC router assumptions 295 In order to achieve its security goals, BGPSEC assumes additional 296 capabilities in routers. In particular, BGPSEC involves adding 297 digital signatures to BGP update messages, which will significantly 298 increase the size of these messages. Therefore, an AS that wishes to 299 receive BGPSEC update messages will require additional memory in its 300 routers to store (e.g., in ADJ RIBs) the data conveyed in these large 301 update messages. Additionally, the design of BGPSEC assumes that an 302 AS that elects to receive BGPSEC update messages will do some 303 cryptographic signature verification at its edge router. This 304 verification will likely require additional capability in these edge 305 routers. 307 For this initial version of BGPSEC, optimizations to minimize the 308 size of BGPSEC updates or the processing required in edge routers 309 were NOT considered. Such optimizations may be considered in the 310 future. 312 Note also that the design of BGPSEC allows an AS to send BGPSEC 313 update messages (thus obtaining protection for routes it originates) 314 without receiving BGPSEC update messages. An AS that only sends, and 315 does not receive, BGPSEC update messages will require much less 316 capability in its edge routers to deploy BGPSEC. In particular, a 317 router that only sends BGPSEC update messages does not need 318 additional memory to store large updates and requires only minimal 319 cryptographic capability (as generating one signature per outgoing 320 update requires less computation than verifying multiple signatures 321 on each incoming update message). See [I-D.ymbk-bgpsec-ops] for 322 further discussion related to Edge ASes that do not provide transit.) 324 4.3. BGPSEC and consistency of externally visible data 326 Finally note that, by design, BGPSEC prevents parties that propagate 327 route advertisements from including inconsistent or erroneous 328 information within the AS-Path (without detection). In particular, 329 this means that any deployed scenarios in which a BGP speaker 330 constructs such an inconsistent or erroneous AS Path attribute will 331 break when BGPSEC is used. 333 For example, when BGPSEC is not used, it is possible for a single 334 autonomous system to have one peering session where it identifies 335 itself as AS 111 and a second peering session where it identifies 336 itself as AS 222. In such a case, it might receive route 337 advertisements from the first peering session (as AS 111) and then 338 add AS 222 (but not AS 111) to the AS-Path and propagate them within 339 the second peering session. 341 Such behavior may very well be innocent and performed with the 342 consent of the legitimate holder of both AS 111 and 222. However, it 343 is indistinguishable from the following man-in-the-middle attack 344 performed by a malicious AS 222. First, the malicious AS 222 345 impersonates AS 111 in the first peering session (essentially 346 stealing a route advertisement intended for AS 111). The malicious AS 347 222 then inserts itself into the AS path and propagates the update to 348 its peers. 350 Therefore, when BGPSEC is used, such an autonomous system would 351 either need to assert a consistent AS number in all external peering 352 sessions, or else it would need to add both AS 111 and AS 222 to the 353 AS-Path (along with appropriate signatures) for route advertisements 354 that it receives from the first peering session and propagates within 355 the second peering session. 357 5. Security Considerations 359 This document provides an overview of BPSEC; it does not define the 360 BGPSEC extension to BGP. The BGPSEC extension is defined in [I- 361 D.lepinski-bgpsec-protocol]. The threat model for the BGPSEC is 362 described in [I-D.kent-bgpsec-threats]. 364 6. IANA Considerations 366 None. 368 7. References 370 7.1. Normative References 372 [RFC4271] Rekhter, Y., Li, T., and S. Hares, Eds., "A Border Gateway 373 Protocol 4 (BGP-4)", RFC 4271, January 2006. 375 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 376 with BGP-4", RFC 5492, February 2009. 378 [I-D.sidr-arch] Lepinski, M. and S. Kent, "An Infrastructure to 379 Support Secure Internet Routing", draft-ietf-sidr-arch, work-in- 380 progress. 382 [I-D.sidr-roa-validation] Huston, G., and G. Michaelson, "Validation 383 of Route Origination using the Resource Certificate PKI and ROAs", 384 draft-ietf-sidr-roa-validation, work-in-progress. 386 [I-D.sidr-origin-ops] Bush, R., "RPKI-Based Origin Validation 387 Operation", draft-ietf-sidr-origin-ops, work-in-progress. 389 [I-D.kent-bgpsec-threats] Kent, S., "Threat Model for BGP Path 390 Security", draft-kent-bgpsec-threats, work-in-progress. 392 [I-D.sidr-bgpsec-protocol] Lepinski, M., Ed., "BPSEC Protocol 393 Specification", draft-ietf-sidr-bgpsec-protocol, work-in-progress. 395 [I-D.ymbk-bgpsec-ops] Bush, R., "BGPSEC Operational Considerations", 396 draft-ymbk-bgpsec-ops, work-in-progress. 398 7.2. Informative References 400 [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", RFC 401 4272, January 2006 403 Author's' Addresses 405 Matt Lepinski 406 BBN Technologies 407 10 Moulton Street 408 Cambridge MA 02138 410 Email: mlepinski@bbn.com 412 Sean Turner 413 IECA, Inc. 414 3057 Nutley Street, Suite 106 415 Fairfax, VA 22031 417 Email: turners@ieca.com