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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: If there does not exist at least one version of BGPSEC that is supported by both peers in a BGP session, then the use of BGPSEC has not been negotiated. (That is, in such a case, messages containing the BGPSEC_Path_Signatures MUST not be sent.) == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: If the BGPSEC speaker is producing an update message which contains an AS-SET (e.g., the BGPSEC speaker is performing proxy aggregation), then the BGPSEC speaker MUST not include the BGPSEC_Path_Signatures attribute. In such a case, the BGPSEC speaker must remove any existing BGPSEC_Path_Signatures in the received advertisement(s) for this prefix and produce a standard (non-BGPSEC) update message. -- The document date (March 7, 2011) is 4770 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: '3' is defined on line 1029, but no explicit reference was found in the text ** Obsolete normative reference: RFC 3447 (ref. '1') (Obsoleted by RFC 8017) -- Duplicate reference: RFC4760, mentioned in '3', was also mentioned in '2'. ** Downref: Normative reference to an Informational draft: draft-ietf-sidr-arch (ref. '7') -- Possible downref: Normative reference to a draft: ref. '8' Summary: 4 errors (**), 0 flaws (~~), 4 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Lepinski, Ed. 3 Internet-Draft BBN 4 Intended status: Standards Track March 7, 2011 5 Expires: September 8, 2011 7 BGPSEC Protocol Specification 8 draft-lepinski-bgpsec-protocol-00.txt 10 Abstract 12 This document describes BGPSEC, a mechanism for providing path 13 security for BGP route advertisements. BGPSEC is implemented via a 14 new optional non-transitive BGP path attribute. 16 Requirements Language 18 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 19 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 20 document are to be interpreted as described in RFC 2119 [4]. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on September 8, 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. BGPSEC Negotiation . . . . . . . . . . . . . . . . . . . . . . 3 58 3. The BGPSEC_Path_Signatures Attribute . . . . . . . . . . . . . 5 59 4. Generating a BGPSEC Update . . . . . . . . . . . . . . . . . . 7 60 4.1. Originating a New BGPSEC Update . . . . . . . . . . . . . 8 61 4.2. Propagating a Route Advertisement . . . . . . . . . . . . 11 62 5. Validating a BGPSEC Update . . . . . . . . . . . . . . . . . . 13 63 5.1. Validation Algorithm . . . . . . . . . . . . . . . . . . . 14 64 6. Algorithms and Extensibility . . . . . . . . . . . . . . . . . 18 65 6.1. Algorithm Suite Considerations . . . . . . . . . . . . . . 18 66 6.2. Extensibility Considerations . . . . . . . . . . . . . . . 19 67 7. Security Considerations . . . . . . . . . . . . . . . . . . . 19 68 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 22 69 8.1. Authors . . . . . . . . . . . . . . . . . . . . . . . . . 22 70 8.2. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 23 71 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 72 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 24 74 1. Introduction 76 This document describes BGPSEC, a mechanism for providing path 77 security for BGP route advertisements. That is, a BGP speaker who 78 receives a valid BGPSEC update has cryptographic assurance that the 79 advertised route has the following two properties: 81 1. The route was originated by an AS that has been explicitly 82 authorized by the holder of the IP address prefix to originate 83 route advertisements for that prefix. 85 2. Every AS listed in the AS_Path attribute of the update explicitly 86 authorized the advertisement of the route to the subsequent AS in 87 the AS_Path. 89 This document specifies a new optional (non-transitive) BGP path 90 attribute, BGPSEC_Path_Signatures. It also describes how a BGPSEC- 91 compliant BGP speaker (referred to hereafter as a BGPSEC speaker) can 92 generate, propagate, and validate BGP update messages containing this 93 attribute to obtain the above assurances. 95 BGPSEC relies on the Resource Public Key Infrastructure (RPKI) 96 certificates that attest to the allocation of AS number and IP 97 address resources. (For more information on the RPKI, see [7] and 98 the documents referenced therein.) Any BGPSEC speaker who wishes to 99 send BGP update messages to external peers (eBGP) containing the 100 BGPSEC_Path_Signatures must have an RPKI end-entity certificate (as 101 well as the associated private signing key) corresponding to the 102 BGPSEC speaker's AS number. Note, however, that a BGPSEC speaker 103 does not require such a certificate in order to validate update 104 messages containing the BGPSEC_Path_Signatures attribute. 106 2. BGPSEC Negotiation 108 This document defines a new BGP capability [3]that allows a BGP 109 speaker to advertise to its neighbors the ability to send and/or 110 receive BGPSEC update messages (i.e., update messages containing the 111 BGPSEC_Path_Signatures attribute). 113 This capability has capability code : TBD 115 The capability length for this capability MUST be set to 3. 117 The three octets of the capability value are specified as follows. 119 Capability Value: 121 0 1 2 3 4 5 6 7 122 +---------------------------------------+ 123 | Send | Receive | Reserved | Version | 124 +---------------------------------------+ 125 | AFI | 126 +---------------------------------------+ 127 | | 128 +---------------------------------------+ 130 The high order bit (bit 0) of the first octet is set to 1 to indicate 131 that the sender is able to send BGPSEC update messages, and is set to 132 zero otherwise. The next highest order bit (bit 1) of this octet is 133 set to 1 to indicate that the sender is able to receive BGPSEC update 134 messages, and is set to zero otherwise. The next two bits of the 135 capability value (bits 2 and 3) are reserved for future use. 137 The four low order bits (4, 5, 6 and 7) of the first octet indicate 138 the version of BGPSEC for which the BGP speaker is advertising 139 support. This document defines only BGPSEC version 0 (all four bits 140 set to zero). Other versions of BGPSEC may be defined in future 141 documents. A BGPSEC speaker MAY advertise support for multiple 142 versions of BGPSEC by including multiple versions of the BGPSEC 143 capability in its BGP OPEN message. 145 If there does not exist at least one version of BGPSEC that is 146 supported by both peers in a BGP session, then the use of BGPSEC has 147 not been negotiated. (That is, in such a case, messages containing 148 the BGPSEC_Path_Signatures MUST not be sent.) 150 If version 0 is the only version of BGPSEC for which both peers (in a 151 BGP session) advertise support, then the use of BGPSEC has been 152 negotiated and the BGPSEC peers MUST adhere to the specification of 153 BGPSEC provided in this document. (If there are multiple versions of 154 BGPSEC which are supported by both peer, then the behavior of those 155 peers is outside the scope of this document.) 157 The second two octets contain the 16-bit Address Family Identifier 158 (AFI) which indicates the address family for which the BGPSEC speaker 159 is advertising support for BGPSEC. This document only specifies 160 BGPSEC for use with two address families, IPv4 and IPv6. BGPSEC for 161 use with other address families may be specified in future documents. 162 Note that if the BGPSEC speaker wishes to use BGPSEC with two 163 different address families (i.e., IPv4 and IPv6) over the same BGP 164 session, then the speaker must include two instances of this 165 capability (one for each address family) in the BGP OPEN message. 166 Also note that a BGPSEC speaker SHOULD NOT advertise the capability 167 of BGPSEC support for IPv6 unless it has also advertised support for 168 IPv6 [2]. 170 By indicating support for receiving BGPSEC update messages, a BGP 171 speaker is, in particular, indicating that the following are true: 173 o The BGP speaker understands the BGPSEC_Path_Signatures attribute 174 (see Section 3). 176 o The BGP speaker supports 4-byte AS numbers (see RFC 4893). 178 Note that BGPSEC update messages can be quite large, therefore any 179 BGPSEC speaker announcing the capability to receive BGPSEC messages 180 SHOULD also announce support for the capability to receive BGP 181 extended messages [5]. 183 A BGP speaker MUST NOT send an update message containing the 184 BGPSEC_Path_Signatures attribute within a given BGP session unless 185 both of the following are true: 187 o The BGP speaker indicated support for sending BGPSEC update 188 messages in its open message. 190 o The peer of the BGP speaker indicated support for receiving BGPSEC 191 update messages in its open message. 193 3. The BGPSEC_Path_Signatures Attribute 195 The BGPSEC_Path_Signatures attribute is a new optional (non- 196 transitive) BGP path attribute. 198 This document registers a new attribute type code for this attribute 199 : TBD 201 The BGPSEC_Path_Signatures attribute has the following structure: 203 BGPSEC_Path_Signatures Attribute 205 +---------------------------------------------------------+ 206 | Expire Time (8 octets) | 207 +---------------------------------------------------------+ 208 | Sequence of one or two Signature-List Blocks (variable) | 209 +---------------------------------------------------------+ 211 Expire Time contains a binary representation of a time as an unsigned 212 integer number of (non-leap) seconds that have elapsed since midnight 213 UTC January 1, 1970. The Expire Time indicates the latest point in 214 time that the route advertised in the update message can possibly be 215 considered valid (see Section 5 for details on validity of BGPSEC 216 update messages). 218 The BGPSEC_Path_Signatures attribute will contain one or two 219 Signature-List Blocks, each of which corresponds to a different 220 algorithm suite. Each of the Signature-List Blocks will contain a 221 signature segment for each AS in the AS Path attribute. In the most 222 common case, the BGPSEC_Path_Signatures attribute will contain only a 223 single Signature-List Block. However, in order to enable a 224 transition from an old algorithm suite to a new algorithm suite, it 225 will be necessary to include two Signature-List Blocks (one for the 226 old algorithm suite and one for the new algorithm suite) during the 227 transition period. 229 Signature-List Block 231 +---------------------------------------------+ 232 | Algorithm Suite Identifier (1 octet) | 233 +---------------------------------------------+ 234 | Signature-List Block Length (2 octets) | 235 +---------------------------------------------+ 236 | Sequence of Signature-Segments (variable) | 237 +---------------------------------------------+ 239 An algorithm suite consists of a digest algorithm and a signature 240 algorithm. This version of BGPSEC only supports signature algorithms 241 that produce a signatures of fixed length. This specification 242 creates an IANA registry of one-octet BGPSEC algorithm suite 243 identifiers. Additionally, this document registers a single 244 algorithm suite which uses the digest algorithm SHA-256 and the 245 signature algorithm RSA with 2048-bit keys [1]. The signatures 246 produced by this algorithm suite have a length of 256 octets. Future 247 registrations of algorithm suites for BGPSEC must specify the length 248 of signatures produced by the algorithm suite. 250 BGPSEC Algorithm Suites 252 Algorithm Suite Digest Signature Specification 253 Identifier Algorithm Algorithm Pointer 254 +-----------------+--------------+----------------+---------------+ 255 | TBA | SHA-256 | RSA 2048 | RFC 3447 | 256 +-----------------+--------------+----------------+---------------+ 258 The Signature-List Block Length is the total number of octets in all 259 Signature-Segments (i.e., the total size of the variable-length 260 portion of the Signature-List block.) 262 A Signature-Segment has the following structure: 264 Signature Segments 266 +-------------------------------------------- + 267 | Subject Key Identifier Length (1 octet) | 268 +---------------------------------------------+ 269 | Subject Key Identifier (variable) | 270 +---------------------------------------------+ 271 | Signature (fixed by algorithm suite) | 272 +---------------------------------------------+ 274 The Subject Key Identifier Length contains the size (in octets) of 275 the value in the Subject Key Identifier field of the Signature- 276 Segment. The Subject Key Identifier contains the value in the 277 Subject Key Identifier extension of the RPKI end-entity certificate 278 that is used to verify the signature (see Section 5 for details on 279 validity of BGPSEC update messages). 281 The Signature contains a digital signature that protects the NLRI, 282 the AS_Path and the BGPSEC_Path_Signatures attribute (see Sections 4 283 and 5 for details on generating and verifying this signature, 284 respectively). The length of the Signature field is a function of 285 the algorithm suite for a given Signature-List Block. The 286 specification for each BGPSEC algorithm suite must provide the length 287 of signatures constructed using the given algorithm suite. 289 4. Generating a BGPSEC Update 291 Sections 4.1 and 4.2 cover two cases in which a BGPSEC speaker may 292 generate an update message containing the BGPSEC_Path_Signatures 293 attribute. The first case is that in which the BGPSEC speaker 294 originates a new route advertisement (Section 4.1). That is, the 295 BGPSEC speaker is constructing an update message in which the only AS 296 to appear in the AS Path attribute is the speaker's own AS (normally 297 appears once but may appear multiple times if AS prepending is 298 applied). The second case is that in which the BGPSEC speaker 299 receives a route advertisement from a peer and then decides to 300 propagate the route advertisement to an external (eBGP) peer (Section 301 4.2). That is, the BGPSEC speaker has received a BGPSEC update 302 message and is constructing a new update message for the same NLRI in 303 which the AS Path attribute will contain AS number(s) other than the 304 speaker's own AS. 306 In the remaining case where the BGPSEC speaker is sending the update 307 message to an internal (iBGP) peer, the BGPSEC speaker populates the 308 BGPSEC_Path_Signatures attribute by copying the 309 BGPSEC_Path_Signatures attribute from the received update message. 310 That is, the BGPSEC_Path_Signatures attribute is copied verbatim. 311 Note that in the case that a BGPSEC speaker chooses to forward to an 312 iBGP peer a BGPSEC update message that has not been successfully 313 validated (see Section 5), the BGPSEC_Path_Signatures attribute 314 SHOULD NOT be removed. (See Section 7 for the security ramifications 315 of removing BGPSEC signatures.) 317 The information protected by the signature on a BGPSEC update message 318 includes the AS number of the peer to whom the update message is 319 being sent. Therefore, if a BGPSEC speaker wishes to send a BGPSEC 320 update to multiple BGP peers, it MUST generate a separate BGPSEC 321 update message for each unique peer AS to which the update message is 322 sent. 324 A BGPSEC update message MUST advertise a route to only a single NLRI. 325 If a BGPSEC speaker wishes to advertise routes to multiple NLRI, then 326 it MUST generate a separate BGPSEC update message for each NLRI. 328 Note that in order to create or add a new signature to a Signature- 329 List Block for a given algorithm suite, the BGPSEC speaker must 330 possess a private key suitable for generating signatures for this 331 algorithm suite. Additionally, this private key must correspond to 332 the public key in a valid Resource PKI end-entity certificate whose 333 AS number resource extension includes the BGPSEC speaker's AS number. 334 Note also new signatures are only added to a BGPSEC update message 335 when a BGPSEC speaker is generating an update message to send to an 336 external peer (i.e., when the AS number of the peer is not equal to 337 the BGPSEC speaker's own AS number). Therefore, a BGPSEC speaker who 338 only sends BGPSEC update messages to peers within its own AS, it does 339 not need to possess any private signature keys. 341 4.1. Originating a New BGPSEC Update 343 In an update message that originates a new route advertisement (i.e., 344 an update whose AS_Path contains, possibly multiple occurrences of, a 345 single AS number), the BGPSEC speaker creates one Signature-List 346 Block for each algorithm suite that will be used. Typically, a 347 BGPSEC speaker will use only a single algorithm suite. However, to 348 ensure backwards compatibility during a period of transition from a 349 'current' algorithm suite to a 'new' algorithm suite, it will be 350 necessary to originate update messages containing Signature-List 351 Blocks for both the 'current' and the 'new' algorithm suites (see 352 Section 6.1). 354 The Resource PKI enables the legitimate holder of IP address 355 prefix(es) to issue a signed object, called a Route Origination 356 Authorization (ROA), that authorizes a given AS to originate routes 357 to a given set of prefixes (see [6]).Note that validation of a BGPSEC 358 update message will fail (i.e., the validation algorithm, specified 359 in Section 5.1, returns 'Not Good') unless there exists a valid ROA 360 authorizing the first AS in the AS PATH attribute to originate routes 361 to the prefix being advertised. Therefore, a BGPSEC speaker SHOULD 362 NOT originate a BGPSEC update advertising a route for a given prefix 363 unless there exists a valid ROA authorizing the BGPSEC speaker's AS 364 to originate routes to this prefix. 366 The Expire Time field is set to specify a time at which the route 367 advertisement specified in the update message will cease to be valid. 368 Once the Expire Time has been reached, all BGPSEC speakers who have 369 received the advertisement will treat it as invalid. The purpose of 370 this field is to protect the BGPSEC speaker against attacks in which 371 the BGPSEC speaker wishes to withdraw the route, but intermediate 372 (malicious) BGP speakers fail to propagate the withdrawal to their 373 peers. 375 It is therefore necessary for the originating BGPSEC speaker to issue 376 a new BGPSEC update prior to reaching the Expire Time. It is 377 RECOMMENDED that a BGPSEC speaker originate a new route advertisement 378 for a given NLRI at intervals equal to roughly one-third the validity 379 period of the route advertisement. (Note that it is necessary to add 380 some small amount of random jitter to the interval to avoid 381 synchronization effects.) For instance, if a BGPSEC speaker is 382 originating route advertisements that are valid for one day (i.e., 383 the Expire Time is 24 hours after the generation of the update 384 message), then it is recommended that the BGPSEC speaker re-issue new 385 a new BGPSEC update message for advertising the given prefix roughly 386 once every 8 hours (plus or minus a small random value). 388 (Editor's Note: The parameter recommendations in the previous 389 paragraph are preliminary and may need to be updated based on further 390 implementation and deployment experience.) 392 There is a natural trade-off in setting the Expire Time. Setting a 393 later Expire Time increases the amount of time by which a malicious 394 intermediate can delay a future route withdrawal. Similarly, setting 395 a later Expire Time also increases the window of opportunity for 396 malicious replay attacks in which a previous BGPSEC announcement is 397 replayed while suppressing a more recent withdrawal for the same 398 prefix. However, setting a sooner Expire Timed increases the 399 frequency with which the BGPSEC speaker needs to send new 400 announcements for the given prefix. 402 When originating a new route advertisement, each Signature-List Block 403 MUST consist of a single Signature-Segment. The following describes 404 how the BGPSEC speaker populates the fields of the Signature-List 405 Block (see Section 3 for more information on the syntax of Signature- 406 List Blocks). 408 The Subject Key Identifier field (see Section 3) is populated with 409 the identifier contained in the Subject Key Identifier extension of 410 the RPKI end-entity certificate used by the BGPSEC speaker. This 411 Subject Key Identifier will be used by recipients of the route 412 advertisement to identify the proper certificate to use in verifying 413 the signature. 415 The Subject Key Identifier Length field is populated with the length 416 (in octets) of the Subject Key Identifier. 418 The Signature field contains a digital signature that binds the NLRI, 419 AS_Path attribute and BGPSEC_Path_Signatures attribute to the RPKI 420 end-entity certificate used by the BGPSEC speaker. The digital 421 signature is computed as follows: 423 o Construct a sequence of octets by concatenating the Expire Time, 424 Target AS Number, Origin AS Number, Algorithm Suite Identifier, 425 and NLRI. The Target AS Number is the AS to whom the BGPSEC 426 speaker intends to send the update message. (Note that the Target 427 AS number is the AS number announced by the peer in the OPEN 428 message of the BGP session within which the update is sent.) The 429 Origin AS number prepend to this sequence the Target AS (the AS to 430 whom the BGPSEC speaker intends to send the update message) and 431 the Origin AS Number refers to the AS of the BGPSEC speaker who is 432 originating the route advertisement. 434 Sequence of Octets to be Signed 435 +---------------------------------------+ 436 | Expire Time (8 octets) | 437 +---------------------------------------+ 438 | Target AS Number (4 octets) | 439 +---------------------------------------+ 440 | Origin AS Number (4 octets) | 441 +---------------------------------------+ 442 | Algorithm Suite Identifier (1 octet) | 443 +---------------------------------------+ 444 | NLRI Length (1 octet) | 445 +---------------------------------------+ 446 | NLRI Prefix (variable) | 447 +---------------------------------------+ 449 o Apply to this octet sequence the digest algorithm (for the 450 algorithm suite of this Signature-List) to obtain a digest value. 452 o Apply to this digest value the signature algorithm, (for the 453 algorithm suite of this Signature-List) to obtain the digital 454 signature. Then populate the Signature Field with this digital 455 signature. 457 4.2. Propagating a Route Advertisement 459 When a BGPSEC speaker receives a BGPSEC update message containing a 460 BGPSEC_Path_Signatures algorithm (with one or more signatures) from a 461 (internal or external) peer, it may choose to propagate the route 462 advertisement by sending to its (internal or external) peers by 463 creating a new BGPSEC advertisement for the same prefix. 465 A BGPSEC speaker MUST NOT generate an update message containing the 466 BGPSEC_Path_Signatures attribute unless it has selected, as the best 467 route to the given prefix, a route that it received in an update 468 message containing the BGPSEC_Path_Signatures attribute. In 469 particular, this means that whenever a BGPSEC speaker generates an 470 update message with a BGPSEC_Path_Signatures attribute that it will 471 possess a received update message for the same prefix that also 472 contains a BGPSEC_Path_Signatures attribute. 474 Additionally, whenever a BGPSEC speaker selects as the best route to 475 a given prefix a route that it received in an update message 476 containing the BGPSEC_Path_Signatures attribute, it is RECOMMENDED 477 that if the BGPSEC speaker chooses to propagate the route that it 478 generate an update message containing the BGPSEC_Path_Signatures 479 attribute. However, a BGPSEC speaker MAY propagate a route 480 advertisement by generating a (non-BGPSEC) update message that does 481 not contain the BGPSEC_Path_Signatures attribute. (See Section 7 for 482 discussion of the security ramifications of removing BGPSEC 483 signatures.) 485 If the BGPSEC speaker is producing an update message which contains 486 an AS-SET (e.g., the BGPSEC speaker is performing proxy aggregation), 487 then the BGPSEC speaker MUST not include the BGPSEC_Path_Signatures 488 attribute. In such a case, the BGPSEC speaker must remove any 489 existing BGPSEC_Path_Signatures in the received advertisement(s) for 490 this prefix and produce a standard (non-BGPSEC) update message. 492 To generate the BGPSEC_Path_Signatures attribute on the outgoing 493 update message, the BGPSEC first copies the Expire Time directly from 494 the received update message to the new update message (that it is 495 constructing). Note that the BGPSEC speaker MUST NOT change the 496 Expire Time as any change to Expire Time will cause the new BGPSEC 497 update message to fail validation (see Section 5). 499 The BGPSEC speaker next removes from the BGPSEC_Path_Signatures 500 attribute any Signature-List Blocks corresponding to algorithm suites 501 that it does not support. The BGPSEC_Path_Signatures attribute for 502 the new update message SHOULD contain a Signature-List Block for 503 every algorithm suite that is both present in the received update 504 message and which is supported by the BGPSEC speaker. 506 Note that the validation algorithm (see Section 5.1) deems a BGPSEC 507 update message to be 'Good' if there is at least one supported 508 algorithm suite (and corresponding Signature-List Block) that is 509 deemed 'Good'. This means that a 'Good' BGPSEC update message may 510 contain Signature-List Blocks which are deemed 'Not Good' (e.g., 511 contain signatures that the BGPSEC is unable to verify). 512 Nonetheless, such Signature-List Blocks MUST NOT be removed. (See 513 Section 7 for a discussion of the security ramifications of this 514 design choice.) 516 For each Signature-List Block corresponding to an algorithm suite 517 that the BGPSEC speaker does support, the BGPSEC speaker then adds a 518 new Signature-Segment to the Signature-List Block. This Signature- 519 Segment is prepended to the list of Signature-Segments (placed in the 520 first position) so that the list of Signature-Segments appears in the 521 same order as the corresponding AS numbers in the AS-Path attribute. 522 The BGPSEC speaker populates the fields of this new signature-segment 523 as follows. 525 The Subject Key Identifier field in the new segment is populated with 526 the identifier contained in the Subject Key Identifier extension of 527 the RPKI end-entity certificate used by the BGPSEC speaker. This 528 Subject Key Identifier will be used by recipients of the route 529 advertisement to identify the proper certificate to use in verifying 530 the signature. 532 The Subject Key Identifier Length field is populated with the length 533 (in octets) of the Subject Key Identifier. 535 The Signature field in the new segment contains a digital signature 536 that binds the NLRI, AS_Path attribute and BGPSEC_Path_Signatures 537 attribute to the RPKI end-entity certificate used by the BGPSEC 538 speaker. The digital signature is computed as follows: 540 o Construct a sequence of octets by concatenating the signature 541 field of the most recent Signature-Segment (the one corresponding 542 to AS from whom the BGPSEC speaker's AS received the announcement) 543 with the Target AS (the AS to whom the BGPSEC speaker intends to 544 send the update message). Note that the Target AS number is the 545 AS number announced by the peer in the OPEN message of the BGP 546 session within which the BGPSEC update message is sent. 548 Sequence of Octets to be Signed 550 +-----------------------------------------------------------+ 551 | Most Recent Signature Field (fixed by algorithm suite) | 552 ------------------------------------------------------------+ 553 | Target AS Number (4 octets) | 554 +-----------------------------------------------------------+ 556 o Apply to this octet sequence the digest algorithm (for the 557 algorithm suite of this Signature-List) to obtain a digest value. 559 o Apply to this digest value the signature algorithm, (for the 560 algorithm suite of this Signature-List) to obtain the digital 561 signature. Then populate the Signature Field with this digital 562 signature. 564 5. Validating a BGPSEC Update 566 Validation of a BGPSEC update messages makes use of data from RPKI 567 certificates and signed Route Origination Authorizations (ROA). In 568 particular, to validate update messages containing the 569 BGPSEC_Path_Signatures attribute, it is necessary that the recipient 570 have access to the following data obtained from valid RPKI 571 certificates and ROAs: 573 o For each valid RPKI end-entity certificate containing an AS Number 574 extension, the AS Number, Public Key and Subject Key Identifier 575 are required 577 o For each valid ROA, the AS Number and the list of IP address 578 prefixes 580 Note that the BGPSEC speaker could perform the validation of RPKI 581 certificates and ROAs on its own and extract the required data, or it 582 could receive the same data from a trusted cache that performs RPKI 583 validation on behalf of (some set of) BGPSEC speakers. 585 To validate a BGPSEC update message containing the 586 BGPSEC_Path_Signatures attribute, the recipient performs the 587 validation steps specified in Section 5.1. The validation procedure 588 results in one of two states: 'Good' and 'Not Good'. 590 It is expected that the output of the validation procedure will be 591 used as an input to BGP route selection. However, BGP route 592 selection and thus the handling of the two validation states is a 593 matter of local policy, and shall be handled using existing local 594 policy mechanisms. It is expected that BGP peers will generally 595 prefer routes received via 'Good' BGPSEC update messages over routes 596 received via 'Not Good' BGPSEC update messages as well as routes 597 received via update messages that do not contain the 598 BGPSEC_Path_Signatures attribute. However, BGPSEC specifies no 599 changes to the BGP decision process and leaves to the operator the 600 selection of an appropriate policy mechanism to achieve the 601 operator's desired results within the BGP decision process. 603 BGPSEC validation need only be performed at eBGP edge. The 604 validation status of a BGP signed/unsigned update MAY be conveyed via 605 iBGP from an ingress edge router to an egress edge router. Local 606 policy in the AS determines the specific means for conveying the 607 validation status through various pre-existing mechanisms such as 608 setting a BGP community, or modifying a metric value such as 609 Local_Pref or MED. As discussed in Section 4, when a BGPSEC speaker 610 chooses to forward a (syntactically correct) BGPSEC update message, 611 it SHOULD be forwarded with its BGPSEC_Path_Signatures attribute 612 intact (regardless of the validation state of the update message). 613 Based entirely on local policy settings, an egress router MAY trust 614 the validation status conveyed by an ingress router or it MAY perform 615 its own validation. 617 5.1. Validation Algorithm 619 This section specifies an algorithm for validation of BGPSEC update 620 messages. A conformant implementation MUST include an BGPSEC update 621 validation algorithm that is functionally equivalent to the external 622 behavior of this algorithm. 624 First, the recipient of a BGPSEC update message performs a check to 625 ensure that the message is properly formed. Specifically, the 626 recipient performs the following checks: 628 o Check to ensure that the entire BGPSEC_Path_Signatures attribute 629 is syntactically correct (conforms to the specification in this 630 document). 632 o Check to ensure that the AS-Path attribute contains no AS-Set 633 segments. 635 o Check that each Signature-List Block contains one Signature- 636 Segment for each AS in the AS-Path attribute. (Note that the 637 entirety of each Signature-List Block must be checked to ensure 638 that it is well formed, even though the validation process may 639 terminate before all signatures are cryptographically verified.) 641 If there are two Signature-List Blocks within the 642 BGPSEC_Path_Signatures attribute and one of them is poorly formed (or 643 contains the wrong number of Signature-Segments) , then the recipient 644 should log that an error occurred, strip off that particular 645 Signature-List Block and process the update message as though it 646 arrived with a single Signature-List Block. If the 647 BGPSEC_Path_Signatures attribute contains a syntax error which is not 648 local to a single Signature-List Block, or if the AS-Path attribute 649 contains an AS-Set segment, then the recipient should log that an 650 error occurred, strip off the BGPSEC_Path_Signatures attribute and 651 process the update message as though it arrived without a 652 BGPSEC_Path_Signatures attribute. 654 Second, the BGPSEC speaker verifies that the update message has not 655 yet expired. To do this, locate the Expire Time field in the 656 BGPSEC_Path_Signatures attribute, and compare it with the current 657 time. If the current time is later than the Expire Time, the BGPSEC 658 update is 'Not Good' and the validation algorithm terminates. 660 Third, the BGPSEC speaker verifies that the origin AS is authorized 661 to advertise the prefix in question. To do this, consult the valid 662 ROA data to obtain a list of AS numbers that are associated with the 663 given IP address prefix in the update message. Then locate the last 664 (least recently added) AS number in the AS-Path. If the origin AS in 665 the AS-Path is not in the set of AS numbers associated with the given 666 prefix, then BGPSEC update message is 'Not Good' and the validation 667 algorithm terminates. 669 Finally, the BGPSEC speaker examines the Signature-List Blocks in the 670 BGPSEC_Path_Signatures attribute. Any Signature-List Block 671 corresponding to an algorithm suite that the BGPSEC speaker does not 672 support MUST be discarded. If all Signature-List Blocks are 673 discarded in this manner then the BGPSEC speaker MUST treat the 674 update message as though it arrived without a BGPSEC_Path_Signatures 675 attribute. 677 For each remaining Signature-List Block (corresponding to an 678 algorithm suite supported by the BGPSEC speaker), the BGPSEC speaker 679 iterates through the Signature-Segments in the Signature-List block, 680 starting with the most recently added segment (and concluding with 681 the least recently added segment). Note that there is a one-to-one 682 correspondence between Signature-Segments and AS numbers in the AS- 683 Path attribute, and the following steps make use of this 684 correspondence. 686 o (Step I): Locate the public key needed to verify the signature (in 687 the current Signature-Segment). To do this, consult the valid 688 RPKI end-entity certificate data and look for an SKI that matches 689 the value in the SKI field of the Signature-Segment. If no such 690 SKI value is found in the valid RPKI data then mark the entire 691 Signature-List Block as 'Not Good' and proceed to the next 692 Signature-List Block. Similarly, if the SKI exists but the AS 693 Number associated with the SKI does NOT match the AS Number (in 694 the AS-Path attribute) which corresponds to the current Signature- 695 Segment, then mark the entire Signature-List Block as 'Not Good' 696 and proceed to the next Signature-List Block. 698 o (Step II): Compute the digest function (for the given algorithm 699 suite) on the appropriate data. If the segment is not the (least 700 recently added) segment corresponding to the origin AS, then the 701 digest function should be computed on the following sequence of 702 octets: 704 Sequence of Octets to be Hashed 706 +-------------------------------------------------+ 707 | Signature Field in the Next Segment (variable) | 708 --------------------------------------------------+ 709 | AS Number of Subsequent AS (4 octets) | 710 +-------------------------------------------------+ 712 The 'Signature Field in the Next Segment' is the Signature field 713 found in the Signature-Segment that is next to be processed (that is, 714 the next most recently added Signature- Segment). 716 For the first segment to be processed (the most recently added 717 segment), the 'AS Number of Subsequent AS' is the AS number of the 718 BGPSEC speaker validating the update message. Note that if a BGPSEC 719 speaker uses multiple AS Numbers (e.g., the BGPSEC speaker is a 720 member of a confederation), the AS number used here MUST be the AS 721 number announced in the OPEN message for the BGP session over which 722 the BGPSEC update was received. 724 For each other Signature-Segment, the 'AS Number of Subsequent AS' is 725 the AS that corresponds to the Signature-Segment added immediately 726 after the one being processed. (That is, find the AS number 727 corresponding to the Signature-Segment currently being processed and 728 the 'AS Number of Subsequent AS' is the next AS number that was added 729 to the AS-Path attribute.) 731 Alternatively, if the segment being processed corresponds to the 732 origin AS, then the digest function should be computed on the 733 following sequence of octets: 735 Sequence of Octets to be Hashed 737 +----------------------------------------+ 738 | Expire Time (8 octets) | 739 -----------------------------------------+ 740 | AS Number of Subsequent AS (4 octets) | 741 +----------------------------------------+ 742 | Origin AS Number (4 octets) | 743 +----------------------------------------+ 744 | Algorithm Suite Identifier (1 octet) | 745 +----------------------------------------+ 746 | NLRI Length (1 octet) | 747 +----------------------------------------+ 748 | NLRI Prefix (variable) | 749 +----------------------------------------+ 751 The NLRI Length, NLRI Prefix, Expire Time, and Algorithm Suite 752 Identifier are all obtained in a straight forward manner from the 753 NLRI of the update message or the BGPSEC_Path_Signatures attribute 754 being validated. 756 The Origin AS Number is the same Origin AS Number that was located in 757 Step I above. (That is, the AS number corresponding to the least 758 recently added Signature-Segment.) 760 The 'AS Number of Subsequent AS' is the AS Number added to the AS- 761 Path immediately after the Origin AS Number. (That is, the second AS 762 Number that was added to the AS Path.) 764 o (Step III): Use the signature validation algorithm (for the given 765 algorithm suite) to verify the signature in the current segment. 766 That is, invoke the signature validation algorithm on the 767 following three inputs: the value of the Signature field in the 768 current segment; the digest value computed in Step II above; and 769 the public key obtained from the valid RPKI data in Step I above. 770 If the signature validation algorithm determines that the 771 signature is invalid, then mark the entire Signature-List Block as 772 'Not Good' and proceed to the next Signature-List Block. If the 773 signature validation algorithm determines that the signature is 774 valid, then continue processing Signature-Segments (within the 775 current Signature-List Block). 777 If all Signature-Segments within a Signature-List Block pass 778 validation (i.e., all segments are processed and the Signature-List 779 Block has not yet been marked 'Not Good'), then the Signature-List 780 Block is marked as 'Good'. 782 If at least one Signature-List Block is marked as 'Good', then the 783 validation algorithm terminates and the BGPSEC update message is 784 deemed to be 'Good'. (That is, if a BGPSEC update message contains 785 two Signature-List Blocks then the update message is deemed 'Good' if 786 the first Signature-List block is marked 'Good' OR the second 787 Signature-List block is marked 'Good'.) 789 6. Algorithms and Extensibility 791 6.1. Algorithm Suite Considerations 793 Note that there is currently no support for bilateral negotiation 794 between BGPSEC peers to use of a particular (digest and signature) 795 algorithm suite using BGP capabilities. This is because the 796 algorithm suite used by the sender of a BGPSEC update message must be 797 understood not only by the peer to whom he is directly sending the 798 message, but also by all BGPSEC speakers to whom the route 799 advertisement is eventually propagated. Therefore, selection of an 800 algorithm suite cannot be a local matter negotiated by BGP peers, but 801 instead must be coordinated throughout the Internet. 803 To this end, a mandatory algorithm suites document will be created 804 which specifies a mandatory-to-use 'current' algorithm suite for use 805 by all BGPSEC speakers. Additionally, the document specifies an 806 additional 'new' algorithm suite that is recommended to implement. 808 It is anticipated that in the future the mandatory algorithm suites 809 document will be updated to specify a transition from the 'current' 810 algorithm suite to the 'new' algorithm suite. During the period of 811 transition (likely a small number of years), all BGPSEC update 812 messages SHOULD simultaneously use both the 'current' algorithm suite 813 and the 'new' algorithm suite. (Note that Sections 3 and 4 specify 814 how the BGPSEC_Path_Signatures attribute can contain signatures, in 815 parallel, for two algorithm suites.) Once the transition is 816 complete, use of the old 'current' algorithm will be deprecated, use 817 of the 'new' algorithm will be mandatory, and a subsequent 'even 818 newer' algorithm suite may be specified as recommend to implement. 819 Once the transition has successfully been completed in this manner, 820 BGPSEC speakers SHOULD include only a single Signature-List Block 821 (corresponding to the 'new' algorithm). 823 6.2. Extensibility Considerations 825 This section discusses potential changes to BGPSEC that would require 826 substantial changes to the processing of the BGPSEC_Path_Signatures 827 and thus necessitate a new version of BGPSEC. Examples of such 828 changes include: 830 o A new type of signature algorithm that produces signatures of 831 variable length 833 o A new type of signature algorithm for which the number of 834 signatures in the Signature-List Block is not equal to the number 835 of ASes in the AS-PATH (e.g., aggregate signatures) 837 o Changes to the data that is protected by the BGPSEC signatures 838 (e.g., protection of attributes other than AS-PATH) 840 In the case that such a change to BGPSEC were deemed desirable, it is 841 expected that a subsequent version of BGPSEC would be created and 842 that this version of BGPSEC would specify a new BGP Path Attribute, 843 let's call it BGPSEC_PATH_SIG_TWO, which is designed to accommodate 844 the desired changes to BGPSEC. In such a case, the mandatory 845 algorithm suites document would be updated to specify algorithm 846 suites appropriate for the new version of BGPSEC. 848 At this point a transition would begin which is analogous to the 849 algorithm transition discussed in Section 6.2. During the transition 850 period all BGPSEC speakers SHOULD simultaneously include both the 851 BGPSEC_PATH_SIGNATURES attribute and the new BGPSEC_PATH_SIG_TWO 852 attribute. Once the transition is complete, the use of 853 BGPSEC_PATH_SIGNATURES could then be deprecated, at which point 854 BGPSEC speakers SHOULD include only the new BGPSEC_PATH_SIG_TWO 855 attribute. Such a process could facilitate a transition to a new 856 BGPSEC semantics in a backwards compatible fashion. 858 7. Security Considerations 860 For discussion of the BGPSEC threat model and related security 861 considerations, please see [8]. 863 A BGPSEC speaker who receives a valid BGPSEC update message, 864 containing a route advertisement for a given prefix, is provided with 865 the following security guarantees: 867 o The origin AS number corresponds to an autonomous system that has 868 been authorized by the IP address space holder to originate route 869 advertisements for the given prefix. 871 o For each subsequent AS number in the AS-Path, a BGPSEC speaker 872 authorized by the holder of the AS number selected the given route 873 as the best route to the given prefix. 875 o For each AS number in the AS Path, a BGPSEC speaker authorized by 876 the holder of the AS number intentionally propagated the route 877 advertisement to the next AS in the AS-Path. 879 That is, the recipient of a valid BGPSEC Update message is assured 880 that the AS-Path corresponds to a sequence of autonomous systems who 881 have all agreed in principle to forward packets to the given prefix 882 along the indicated path. (It should be noted BGPSEC does not offer 883 a precise guarantee that the data packets would propagate along the 884 indicated path; it only guarantees that the BGP update conveying the 885 path indeed propagated along the indicated path.) Furthermore, the 886 recipient is assured that this path terminates in an autonomous 887 system that has been authorized by the IP address space holder as a 888 legitimate destination for traffic to the given prefix. 890 Note that there may be cases where a BGPSEC speaker deems 'Good' (as 891 per the validation algorithm in Section 5.1) a BGPSEC update message 892 that contains both a 'Good' and a 'Not Good' Signature-List Block. 893 That is, the update message contains two sets of signatures 894 corresponding to two algorithm suites, and one set of signatures 895 verifies correctly and the other set of signatures fails to verify. 896 In this case, the protocol specifies that if the BGPSEC speaker 897 propagates the route advertisement received in such an update message 898 then the BGPSEC speaker SHOULD add its signature to each of the 899 Signature-List Blocks using both the corresponding algorithm suite. 900 Thus the BGPSEC speaker creates a signature using both algorithm 901 suites and creates a new update message that contains both the 'Good' 902 and the 'Not Good' set of signatures (from its own vantage point). 904 To understand the reason for such a design decision consider the case 905 where the BGPSEC speaker receives an update message with both a set 906 of algorithm A signatures which are 'Good' and a set of algorithm B 907 signatures which are 'Not Good'. In such a case it is possible 908 (perhaps even quite likely) that some of the BGPSEC speaker's peers 909 (or other entities further 'downstream' in the BGP topology) do not 910 support algorithm A. Therefore, if the BGPSEC speaker were to remove 911 the 'Not Good' set of signatures corresponding to algorithm B, such 912 entities would treat the message as though it were unsigned. By 913 including the 'Not Good' set of signatures when propagating a route 914 advertisement, the BGPSEC speaker ensures that 'downstream' entities 915 have as much information as possible to make an informed opinion 916 about the validation status of a BGPSEC update. 918 Note also that during a period of partial BGPSEC deployment, a 919 'downstream' entity might reasonably treat unsigned messages 920 different from BGPSEC updates that contain a single set of 'Not Good' 921 signatures. That is, by removing the set of 'Not Good' signatures 922 the BGPSEC speaker might actually cause a downstream entity to 923 'upgrade' the status of a route advertisement from 'Not Good' to 924 unsigned. Finally, note that in the above scenario, the BGPSEC 925 speaker might have deemed algorithm A signatures 'Good' only because 926 of some issue with RPKI state local to his AS (for example, his AS 927 might not yet have obtained a CRL indicating that a key used to 928 verify an algorithm A signature belongs to a newly revoked 929 certificate). In such a case, it is highly desirable for a 930 downstream entity to treat the update as 'Not Good' (due to the 931 revocation) and not as 'unsigned' (which would happen if the 'Not 932 Good' Signature-List Blocks were removed). 934 A similar argument applies to the case where a BGPSEC speaker (for 935 some reason such as lack of viable alternatives) selects as his best 936 route to a given prefix a route obtained via a 'Not Good' BGPSEC 937 update message. (That is, a BGPSEC update containing only 'Not Good' 938 Signature-List Blocks.) In such a case, the BGPSEC speaker should 939 propagate a signed BGPSEC update message, adding his signature to the 940 'Not Good' signatures that already exist. Again, this is to ensure 941 that 'downstream' entities are able to make an informed decision and 942 not erroneously treat the route as unsigned. It may also be noted 943 here that due to possible differences in RPKI data at different 944 vantage points in the network, a BGPSEC update that was deemed 'Not 945 Good' at an upstream BGPSEC speaker may indeed be deemed 'Good' at 946 another BGP speaker downstream. 948 Therefore, it is important to note that when a BGPSEC speaker signs 949 an outgoing update message, it is not attesting to a belief that all 950 signatures prior to its are valid. Instead it is merely asserting 951 that: 953 1. The BGPSEC speaker received the given route advertisement with 954 the indicated NLRI and AS Path; 956 2. The BGPSEC speaker selected this route as the best route to the 957 given prefix; and 959 3. The BGPSEC speaker chose to propagate an advertisement for this 960 route to the peer (implicitly) indicated by the 'Target AS' 962 The BGPSEC update validation procedure is a potential target for 963 denial of service attacks against a BGPSEC speaker. To mitigate the 964 effectiveness of such denial of service attacks, BGPSEC speakers 965 should implement an update validation algorithm that performs 966 expensive checks (e.g., signature verification) after less expensive 967 checks (e.g., syntax checks). The validation algorithm specified in 968 Section 5.1 was chosen so as to perform checks which are likely to be 969 expensive after checks that are likely to be inexpensive. However, 970 the relative cost of performing required validation steps may vary 971 between implementations, and thus the algorithm specified in Section 972 5.1 may not provide the best denial of service protection for all 973 implementations. 975 8. Contributors 977 8.1. Authors 979 Rob Austein 980 Internet Systems Consortium 981 sra@hactrn.net 983 Steven Bellovin 984 Columbia University 985 smb@cs.columbia.edu 987 Randy Bush 988 Internet Initiative Japan 989 randy@psg.com 991 Russ Housley 992 Vigil Security 993 housley@vigilsec.com 995 Stephen Kent 996 BBN Technologies 997 kent@bbn.com 999 Warren Kumari 1000 Google 1001 warren@kumari.net 1003 Doug Montgomery 1004 USA National Institute of Standards and Technology 1005 dougm@nist.gov 1007 Kotikalapudi Sriram 1008 USA National Institute of Standards and Technology 1009 kotikalapudi.sriram@nist.gov 1011 Samuel Weiler 1012 weiler@watson.org 1013 Cobham 1015 8.2. Acknowledgements 1017 The authors would like to thank Sharon Goldberg, Ed Kern, Chris 1018 Morrow, Sandy Murphy, Mark Reynolds, Heather Schiller, Jason 1019 Schiller, John Scudder, and David Ward for their valuable input and 1020 review. 1022 9. References 1024 [1] Jonsson, J. and B. Kaliski, "PKCS #1", RFC 3447, February 2003. 1026 [2] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol 1027 Extensions for BGP-4", RFC 4760, January 2007. 1029 [3] Scudder, J. and R. Chandra, "Capabilities Advertisement with 1030 BGP-4", RFC 4760, February 2009. 1032 [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement 1033 Levels", BCP 14, RFC 2119, March 1997. 1035 [5] Patel, K., Ward, D., and R. Bush, "Extended Message support for 1036 BGP", draft-ymbk-bgp-extended-messages, March 2011. 1038 [6] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route Origin 1039 Authorizations", draft-ietf-sidr-roa-format, February 2011. 1041 [7] Lepinski, M. and S. Kent, "An Infrastructure to Support Secure 1042 Internet Routing", draft-ietf-sidr-arch, February 2011. 1044 [8] Kent, S., "Threat Model for BGP Path Security", 1045 draft-kent-bgpsec-threats, February 2011. 1047 Author's Address 1049 (Editor) Matthew Lepinski 1050 BBN 1051 10 Moulton St 1052 Cambridge, MA 55409 1054 Phone: +1-617-873-5939 1055 Email: mlepinski@bbn.com