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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-16) exists of draft-ietf-sidr-bgpsec-ops-06 == Outdated reference: A later version (-23) exists of draft-ietf-sidr-bgpsec-protocol-12 == Outdated reference: A later version (-16) exists of draft-ietf-sidr-rtr-keying-08 Summary: 0 errors (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group R. Gagliano 3 Internet-Draft K. Patel 4 Intended status: Standards Track B. Weis 5 Expires: January 7, 2016 Cisco Systems 6 July 6, 2015 8 BGPsec Router Certificate Rollover 9 draft-ietf-sidr-bgpsec-rollover-04 11 Abstract 13 BGPsec will need to address the impact from regular and emergency 14 rollover processes for the BGPsec End-Entity (EE) certificates that 15 will be performed by Certificate Authorities (CAs) participating at 16 the Resource Public Key Infrastructure (RPKI). Rollovers of BGPsec 17 EE certificates must be carefully managed in order to synchronize 18 distribution of router public keys and the usage of those pubic keys 19 by BGPsec routers. This document provides general recommendations 20 for that process, as well as describing reasons why the rollover of 21 BGPsec EE certificates might be necessary. 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on January 7, 2016. 40 Copyright Notice 42 Copyright (c) 2015 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3 58 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 3. Key rollover in BGPsec . . . . . . . . . . . . . . . . . . . . 6 60 3.1. A proposed process for BGPsec key rollover . . . . . . . . 6 61 4. BGPsec key rollover as a measure against replays attacks 62 in BGPsec . . . . . . . . . . . . . . . . . . . . . . . . . . 9 63 4.1. BGPsec Replay attack window requirement . . . . . . . . . 9 64 4.2. BGPsec key rollover as a mechanism to protect against 65 replay attacks . . . . . . . . . . . . . . . . . . . . . . 9 66 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 67 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 68 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 69 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 70 8.1. Normative References . . . . . . . . . . . . . . . . . . . 14 71 8.2. Informative References . . . . . . . . . . . . . . . . . . 14 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 74 1. Requirements notation 76 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 77 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 78 document are to be interpreted as described in [RFC2119]. 80 2. Introduction 82 In BGPsec, a key rollover (or re-keying) is the process of changing a 83 router's key pair (or pairs), issuing the corresponding new End- 84 Entity certificate and (if the old certificate is still valid) 85 revoking the old certificate. This process will need to happen at 86 regular intervals, normally due to local policies at each network. 87 This document provides general recommendations for that process. 88 Certificate Practice Statements (CPS) documents MAY reference these 89 recommendations. This memo only addresses changing of a router's key 90 pair within the RPKI. Refer to [RFC6489] for a procedure to rollover 91 RPKI Certificate Authority key pairs. 93 When a router receives or creates a new key pair (depending on the 94 key provisioning mechanism to be selected), this key pair will be 95 used to sign new BGPsec_Path attributes 96 [I-D.ietf-sidr-bgpsec-protocol] that are originated or that transit 97 through the BGP speaker. Additionally, the BGP speaker MUST refresh 98 its outbound BGPsec Update messages to include a signature using the 99 new key (replacing the replaced key). When the rollover process 100 finishes, the old BGPsec certificate (and its key) will not longer be 101 valid and thus any BGPsec Update that includes a BGPsec_Path 102 attribute with a signature performed by the old key will be invalid. 103 Consequently, if the router does not refresh its outbound BGPsec 104 Update messages, routing information may be treated as 105 unauthenticated after the rollover process is finished. It is 106 therefore extremely important that the BGPsec router key rollover be 107 performed such that the probability of new router EE certificates 108 have been distributed throughout the RPKI before the router begin 109 signing BGPsec_Path attributes with a new private key. 111 It is also important for an AS to minimize the BGPsec router key 112 rollover interval (i.e., in between the time an AS distributes an EE 113 certificate with a new public key and the time a BGPsec router begins 114 to use its new private key). This can be due to a need for a BGPsec 115 router to distribute BGPsec_Path attributes signed with a new private 116 key in order to invalidate BGPsec_Path attributes signed with the old 117 private key. In particular, if the AS suspects that a stale 118 BGPsec_Path attribute is being distributed instead of the most 119 recently signed attribute it can cause the stale BGPsec_Path 120 attribute to be invalidated by completing a key rollover procedure. 121 The BGPsec rollover interval can be minimized when an automated 122 certificate provisioning process such as Enrollment over Secure 123 Transport (EST) [RFC7030]) is used. 125 The Security Requirements for BGP Path Validation [RFC7353] also 126 describes the need for protecting against the replay of BGP UPDATE 127 messages, such as controlling BGPsec's window of exposure to replay 128 attacks. The BGPsec rollover method in this document can be used to 129 achieve this goal. 131 In [I-D.ietf-sidr-rtr-keying], the "operator-driven" method is 132 introduced, in which a key pair can be shared among different BGP 133 Speakers. In this scenario, the roll-over of the correspondent 134 BGPsec certificate will impact all the BGP Speakers sharing the same 135 private key. 137 3. Key rollover in BGPsec 139 An BGPsec EE certificate SHOULD be replaced when the following events 140 occur, and can be replaced for any other reason at the discretion of 141 the AS responsible for the EE certificate. 143 BGPsec scheduled rollover: BGPsec certificates have an expiration 144 date (NotValidAfter) that requires a frequent rollover process. 145 The validity period for these certificates is typically 146 expressed at the CA's CPS document. 148 BGPsec certificate fields changes: Information contained in a BGPsec 149 certificate (such as the ASN or the Subject) may need to be 150 changed. 152 BGPsec emergency rollover Some special circumstances (such as a 153 compromised key) may require the replacement of a BGPsec 154 certificate. 156 BGPsec signature anti-replay protection An AS may determine stale 157 BGPsec_Path attributes signed by the AS are being propagated 158 instead of the most recently signed BGPsec_Path attributes. 159 Changing the BGPsec router signing key, distributing a new 160 BGPsec EE certificate for the router,and revoking the old 161 BGPsec EE certificate will invalidate the replayed BGPsec_Path 162 attributes. 164 In some of these cases it is possible to generate a new certificate 165 without changing the key pair. This practice simplifies the rollover 166 process as the corresponding BGP speakers do not even need to be 167 aware of the changes to its correspondent certificate. However, not 168 replacing the certificate key for a long period of time increases the 169 risk that the router private key may be compromised. Distributing 170 the OLD public key in a new certificate is NOT RECOMMENDED when the 171 rollover event is due to the key has been compromised or stale 172 BGPsec_Path attribute signatures are being distributed. 174 3.1. A proposed process for BGPsec key rollover 176 The BGPsec key rollover process will be dependent on the key 177 provisioning mechanisms that are adopted by an AS. The key 178 provisioning mechanisms for BGPsec are not yet fully documented (see 179 [I-D.ietf-sidr-rtr-keying] as a work in progress document). It is 180 assumed that an automatic provisioning mechanism such as EST will be 181 in place as such a provisioning mechanism will allow BGPsec code to 182 include automatic re-keying scripts with minimum development cost. 184 If we work under the assumption that an automatic mechanism will 185 exist to rollover a BGPsec certificate, a RECOMMENDED process is as 186 follows. 188 1. New Certificate Publication: The first step in the rollover 189 mechanism is to publish the new public key in a new certificate. 190 In order to accomplish this goal, the new key pair and 191 certificate will need to be generated and published at the 192 appropriate RPKI repository publication point. The details of 193 this process will vary as they depend on whether the keys are 194 assigned per-BGP speaker or shared, whether the keys are 195 generated on each BGP speaker or in a central location and 196 whether the RPKI repository is locally or externally hosted. 198 2. Staging Period: A staging period will be required from the time a 199 new certificate is published in the RPKI global repository until 200 the time it is fetched by RPKI caches around the globe. The 201 exact minimum staging time will be dictated by the conventional 202 interval chosen between repository fetches. If rollovers will be 203 done more frequently, an administrator can provision two 204 certificates for every router concurrently with different valid 205 start times. In this case when the rollover operation is needed, 206 the relying parties around the globe would already have the new 207 keys. A staging period may not be possible to implement during 208 emergency key rollover, in which case routing information may be 209 lost. 211 3. Twilight: At this moment, the BGP speaker that holds the private 212 key that has been rolled-over will stop using the OLD key for 213 signing and start using the NEW key. Also, the router will 214 generate appropriate BGPsec_Path attributes just as in the 215 typical operation of refreshing out-bound BGP polices. This 216 operation may generate a great number of BGPsec_Path attributes 217 (due to the need to refresh BGP outbound policies). In any given 218 BGP SPEAKER, the Twilight moment may be different for every peer 219 in order to distribute the system load (probably in the order of 220 minutes to avoid reaching any expiration time). 222 4. Certificate Revocation: This is an optional step, but SHOULD be 223 taken when the goal is to invalidate signatures used with the OLD 224 key. Reasons to invalidate OLD signatures include when the AS 225 has reason to believe that the router signing key has been 226 compromised, and when the AS needs to invalidate BGPsec_Path 227 attribute signatures used with this key. As part of the rollover 228 process, a CA MAY decide to revoke the OLD certificate by 229 publishing its serial number on the CA's CRL. On the other side, 230 the CA will just let the OLD certificate to expire and not revoke 231 it. This choice will depend on the reasons that motivated the 232 rollover process. 234 5. RPKI-Router Protocol Withdrawals: At the expiration of the OLD 235 certificate's validation, the RPKI relying parties around the 236 globe will need to communicate to their router peers that the OLD 237 certificate's public key is not longer valid (e.g., using the 238 RPKI-Router Protocol described in [RFC6810]). It is not 239 documented yet what will be a router's reaction to a message with 240 the withdrawal bit set to 1 in the RPKI-Router Protocol, but it 241 should include the removal of any RIB entry that includes a 242 BGPsec attribute signed with that key and the generation of the 243 correspondent BGP WITHDRAWALs (either implicit or explicit). 245 The proposed rollover mechanism will depend on the existence of an 246 automatic provisioning process for BGPsec certificates. It will 247 require a staging mechanism based on the RPKI propagation time of 248 around 24 hours, and it will generate BGPsec_Path attributes for all 249 prefixes in the router been re-keyed. 251 The first two steps (New Certificate Publication and Staging Period) 252 may happen in advance of the rest of the process. This will allow a 253 network operator to accelerate its subsequent key roll-over. 255 When a new BGPsec certificate is generated without changing its key, 256 steps 3 (Twilight) and 5 (RPKI-Router Protocol Withdrawals) SHOULD 257 NOT be executed. 259 4. BGPsec key rollover as a measure against replays attacks in BGPsec 261 There are two typical generic measures to mitigate replay attacks in 262 any protocol: the addition of a timestamp or the addition of a serial 263 number. However neither BGP nor BGPsec provide either measure. This 264 section discusses the use of BGPsec Rollover as a measure to mitigate 265 replay attacks. 267 4.1. BGPsec Replay attack window requirement 269 In [RFC7353] Section 4.3, the need to limit the vulnerability to 270 replay attacks is described. One important comment is that during a 271 window of exposure, a replay attack is effective only in very 272 specific circumstances: there is a downstream topology change that 273 makes the signed AS path no longer current, and the topology change 274 makes the replayed route preferable to the route associated with the 275 new update. In particular, if there have been no topology change at 276 all, then no security threat comes from a replay of a BGPsec_Path 277 attribute because the signed information is still valid. 279 The BGPsec Ops document [I-D.ietf-sidr-bgpsec-ops] gives some ideas 280 of requirements for the size of the BGPsec windows of exposure to 281 replay attacks. At that document, it is stated that for the vast 282 majority of the prefixes, the requirement will be in the order of 283 days or weeks. 285 4.2. BGPsec key rollover as a mechanism to protect against replay 286 attacks 288 Since the window requirement is in the order of a day (as documented 289 in [I-D.ietf-sidr-bgpsec-ops]) and the BGP speaker re-keying is the 290 edge router of the origin AS, it is feasible for a BGPsec Rollover to 291 mitigate replays. In this case it is important to complete the full 292 process (i.e. the OLD and NEW certificate do not share the same key). 293 By re-keying an AS is letting the BGPsec certificate validation time 294 be a sort of "timestamp" against replay attacks. However, the use of 295 frequent key rollovers comes with an additional administrative cost 296 and risks if the process fails. As documented before, re-keying 297 should be supported by automatic tools and for the great majority of 298 the Internet it will be done with good lead time to correct any risk. 300 For a transit AS that also originates BGPsec_Path attributes for its 301 own prefixes, the key rollover process may generate a large number of 302 UPDATE messages (even the complete Default Free Zone or DFZ). For 303 this reason, it is recommended that routers in this scenario been 304 provisioned with two certificates: one to sign BGPsec_Path attributes 305 in transit and a second one to sign an BGPsec_Path attribute for 306 prefixes originated in its AS. Only the second certificate (for 307 prefixes originated in its AS) should be rolled-over frequently as a 308 means of limiting replay attach windows. The transit BGPsec 309 certificate is expected to be longer living than the origin BGPsec 310 certificate. 312 Advantage of Re-keying as replay attack protection mechanism: 314 1. All expiration policies are maintained in RPKI 316 2. Much of the additional administrative cost is paid by the 317 provider that wants to protect its infrastructure, as it bears 318 the human cost of creating and initiating distribution of new 319 router key pairs and router EE certificates. (It is true that 320 the cost of relying parties will be affected by the new objects, 321 but their responses should be completely automated or otherwise 322 routine.) 324 3. Can be implemented in coordination with planned topology changes 325 by either origin ASes or transit ASes (e.g., if an AS changes 326 providers, it completes a BGP Rollover) 328 Disadvantage of Re-keying as replay attack protection mechanism: 330 1. More administrative load due to frequent rollover, although how 331 frequent is still not clear. Some initial ideas in 332 [I-D.ietf-sidr-bgpsec-ops] 334 2. Minimum window size bounded by RPKI propagation time to RPKI 335 caches for new certificate and CRL (2x propagation time). If 336 provisioning is done ahead of time the minimum window size is 337 reduced (to 1x propagation time for the CRL). However, more 338 experimentation is needed when RPKI and RPs are more massively 339 deployed. 341 3. Increases dynamics and size of RPKI repository. 343 5. IANA Considerations 345 No IANA considerations 347 6. Security Considerations 349 Several possible reasons can cause routers participating in BGPsec to 350 replace rollover their signing keys and/or signatures containing 351 their current signature verification key. Some reasons are due to 352 the usual key management operations reasons (e.g.,key exposure, 353 change of certificate attributes, due to policy). However BGPsec 354 routers also may need to change their signing keys and associated 355 certificate as an anti-replay protection. 357 The BGPsec Rollover method allows for an expedient rollover process 358 when router certificates are distributed through the RPKI, but 359 without causing routing failures due to a receiving router not being 360 able to validate a BGPsec_Path attribute created by a router that is 361 the subject of the rollover. 363 7. Acknowledgements 365 We would like to acknowledge Randy Bush, Sriram Kotikalapudi, Stephen 366 Kent and Sandy Murphy. 368 8. References 370 8.1. Normative References 372 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 373 Requirement Levels", BCP 14, RFC 2119, March 1997. 375 8.2. Informative References 377 [I-D.ietf-sidr-bgpsec-ops] 378 Bush, R., "BGPsec Operational Considerations", 379 draft-ietf-sidr-bgpsec-ops-06 (work in progress), 380 July 2015. 382 [I-D.ietf-sidr-bgpsec-protocol] 383 Lepinski, M., "BGPsec Protocol Specification", 384 draft-ietf-sidr-bgpsec-protocol-12 (work in progress), 385 June 2015. 387 [I-D.ietf-sidr-rtr-keying] 388 Patel, K. and R. Bush, "Router Keying for BGPsec", 389 draft-ietf-sidr-rtr-keying-08 (work in progress), 390 January 2015. 392 [RFC6489] Huston, G., Michaelson, G., and S. Kent, "Certification 393 Authority (CA) Key Rollover in the Resource Public Key 394 Infrastructure (RPKI)", BCP 174, RFC 6489, February 2012. 396 [RFC6810] Bush, R. and R. Austein, "The Resource Public Key 397 Infrastructure (RPKI) to Router Protocol", RFC 6810, 398 January 2013. 400 [RFC7030] Pritikin, M., Yee, P., and D. Harkins, "Enrollment over 401 Secure Transport", RFC 7030, October 2013. 403 [RFC7353] Bellovin, S., Bush, R., and D. Ward, "Security 404 Requirements for BGP Path Validation", RFC 7353, 405 August 2014. 407 Authors' Addresses 409 Roque Gagliano 410 Cisco Systems 411 Avenue des Uttins 5 412 Rolle, VD 1180 413 Switzerland 415 Email: rogaglia@cisco.com 417 Keyur Patel 418 Cisco Systems 419 170 W. Tasman Drive 420 San Jose, CA 95134 421 CA 423 Email: keyupate@cisco.com 425 Brian Weis 426 Cisco Systems 427 170 W. Tasman Drive 428 San Jose, CA 95134 429 CA 431 Email: bew@cisco.com