BGPsec Router Certificate Rollover
The information below is for an old version of the document.
This is an older version of an Internet-Draft that was ultimately published as RFC 8634.
|Authors||Brian Weis , Roque Gagliano , Keyur Patel|
|RFC stream||Internet Engineering Task Force (IETF)|
RTGDIR Last Call review (of -02) Has Issues
|Additional resources||Mailing list discussion|
|Stream||WG state||WG Document|
|IESG||IESG state||I-D Exists|
|Send notices to||(None)|
Network Working Group B. Weis Internet-Draft R. Gagliano Intended status: Standards Track Cisco Systems Expires: September 9, 2017 K. Patel Arrcus, Inc. March 8, 2017 BGPsec Router Certificate Rollover draft-ietf-sidrops-bgpsec-rollover-00 Abstract BGPsec will need to address the impact from regular and emergency rollover processes for the BGPsec end-entity (EE) certificates that will be performed by Certificate Authorities (CAs) participating at the Resource Public Key Infrastructure (RPKI). Rollovers of BGPsec EE certificates must be carefully managed in order to synchronize distribution of router public keys and the usage of those public keys by BGPsec routers. This memo provides general recommendations for that process, as well as describing reasons why the rollover of BGPsec EE certificates might be necessary. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 9, 2017. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of Weis, et al. Expires September 9, 2017 [Page 1] Internet-Draft BGPsec rollover March 2017 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Requirements notation . . . . . . . . . . . . . . . . . . . . 2 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Key rollover in BGPsec . . . . . . . . . . . . . . . . . . . 3 3.1. A proposed process for BGPsec key rollover . . . . . . . 4 4. BGPsec key rollover as a measure against replays attacks in BGPsec . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. BGPsec Replay attack window requirement . . . . . . . . . 6 4.2. BGPsec key rollover as a mechanism to protect against replay attacks . . . . . . . . . . . . . . . . . . . . . 7 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References . . . . . . . . . . . . . . . . . . 8 8.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Requirements notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Introduction In BGPsec, a key rollover (or re-key) is the process of changing a router's key pair (or key pairs), issuing the corresponding new end- entity (EE) certificate and (if the old certificate is still valid) revoking the old certificate. This process will need to happen at regular intervals, normally due to the local policies of a network. This document provides general recommendations for that process. Certificate Practice Statements (CPS) documents MAY reference these recommendations. This memo only addresses changing of a router's key pair within the RPKI. Refer to [RFC6489] for a procedure to rollover RPKI Certificate Authority key pairs. When a router receives or creates a new key pair (using a key provisioning mechanism), this key pair will be used to sign new Weis, et al. Expires September 9, 2017 [Page 2] Internet-Draft BGPsec rollover March 2017 BGPsec_Path attributes [I-D.ietf-sidr-bgpsec-protocol] that are originated or that transit through the BGP speaker. Additionally, the BGP speaker MUST refresh its outbound BGPsec Update messages to include a signature using the new key (replacing the replaced key). When the rollover process finishes, the old BGPsec certificate (and its key) will not longer be valid, and thus any BGPsec Update that includes a BGPsec_Path attribute with a signature performed by the old key will be invalid. Consequently, if the router does not refresh its outbound BGPsec Update messages, routing information may be treated as unauthenticated after the rollover process is finished. It is therefore extremely important that the BGPsec router key rollover be performed in such a way that the probability of new router EE certificates have been distributed throughout the RPKI before the router begin signing BGPsec_Path attributes with a new private key. It is also important for an AS to minimize the BGPsec router key rollover interval (i.e., in between the time an AS distributes an EE certificate with a new public key and the time a BGPsec router begins to use its new private key). This can be due to a need for a BGPsec router to distribute BGPsec_Path attributes signed with a new private key in order to invalidate BGPsec_Path attributes signed with the old private key. In particular, if the AS suspects that a stale BGPsec_Path attribute is being distributed instead of the most recently signed attribute it can cause the stale BGPsec_Path attribute to be invalidated by completing a key rollover procedure. The BGPsec rollover interval can be minimized when an automated certificate provisioning process such as Enrollment over Secure Transport (EST) [RFC7030]) is used. The Security Requirements for BGP Path Validation [RFC7353] also describes the need for protecting against the replay of BGP UPDATE messages, such as controlling BGPsec's window of exposure to replay attacks. The BGPsec rollover method in this document can be used to achieve this goal. In [I-D.ietf-sidr-rtr-keying], the "operator-driven" method is introduced, in which a key pair can be shared among different BGP Speakers. In this scenario, the roll-over of the correspondent BGPsec certificate will impact all the BGP Speakers sharing the same private key. 3. Key rollover in BGPsec An BGPsec EE certificate SHOULD be replaced when the following events occur, and can be replaced for any other reason at the discretion of the AS responsible for the EE certificate. Weis, et al. Expires September 9, 2017 [Page 3] Internet-Draft BGPsec rollover March 2017 BGPsec scheduled rollover: BGPsec certificates have an expiration date (NotValidAfter) that requires a frequent rollover process. The validity period for these certificates is typically expressed at the CA's CPS document. BGPsec certificate fields changes: Information contained in a BGPsec certificate (such as the ASN or the Subject) may need to be changed. BGPsec emergency rollover Some special circumstances (such as a compromised key) may require the replacement of a BGPsec certificate. BGPsec signature anti-replay protection An AS may determine stale BGPsec_Path attributes signed by the AS are being propagated instead of the most recently signed BGPsec_Path attributes. Changing the BGPsec router signing key, distributing a new BGPsec EE certificate for the router, and revoking the old BGPsec EE certificate will invalidate the replayed BGPsec_Path attributes. In some of these cases it is possible to generate a new certificate without changing the key pair. This practice simplifies the rollover process as the corresponding BGP speakers do not even need to be aware of the changes to its correspondent certificate. However, not replacing the certificate key for a long period of time increases the risk that a compromised router private key may be used by an attacker to deliver unauthorized BGPsec Updates. Distributing the OLD public key in a new certificate is NOT RECOMMENDED when the rollover event is due to the key being compromised, or when stale BGPsec_Path attribute signatures are being distributed. 3.1. A proposed process for BGPsec key rollover The BGPsec key rollover process will be dependent on the key provisioning mechanisms that are adopted by an AS. The key provisioning mechanisms for BGPsec are not yet fully documented (see [I-D.ietf-sidr-rtr-keying] as a work in progress document). An automatic provisioning mechanism such as EST will allow BGPsec code to include automatic re-keying scripts with minimum development cost. If we work under the assumption that an automatic mechanism will exist to rollover a BGPsec certificate, a RECOMMENDED process is as follows. 1. New Certificate Publication: The first step in the rollover mechanism is to publish the new public key in a new certificate. In order to accomplish this goal, the new key pair and Weis, et al. Expires September 9, 2017 [Page 4] Internet-Draft BGPsec rollover March 2017 certificate will need to be generated and the certificate published at the appropriate RPKI repository publication point. The details of this process will vary as they depend on whether the keys are assigned per-BGP speaker or shared, whether the keys are generated on each BGP speaker or in a central location, and whether the RPKI repository is locally or externally hosted. 2. Staging Period: A staging period will be required from the time a new certificate is published in the RPKI global repository until the time it is fetched by RPKI caches around the globe. The exact minimum staging time will be dictated by the conventional interval chosen between repository fetches. If rollovers will be done more frequently, an administrator can provision two certificates for every router concurrently with different valid start times. In this case when the rollover operation is needed, the relying parties around the globe would already have the new router public keys. A staging period may not be possible to implement during emergency key rollover, in which case routing information may be lost. 3. Twilight: At this moment, the BGP speaker that holds the private key that has been rolled-over will stop using the OLD key for signing and start using the NEW key. Also, the router will generate appropriate BGPsec_Path attributes just as in the typical operation of refreshing out-bound BGP polices. This operation may generate a great number of BGPsec_Path attributes (due to the need to refresh BGP outbound policies). In any given BGP SPEAKER, the Twilight moment may be different for every peer in order to distribute the system load (probably in the order of minutes to avoid reaching any expiration time). 4. Certificate Revocation: This is an optional step, but SHOULD be taken when the goal is to invalidate signatures used with the OLD key. Reasons to invalidate OLD signatures include: when the AS has reason to believe that the router signing key has been compromised, and when the AS needs to invalidate BGPsec_Path attribute signatures used with this key. As part of the rollover process, a CA MAY decide to revoke the OLD certificate by publishing its serial number on the CA's CRL. Alternatively, the CA will just let the OLD certificate to expire and not revoke it. This choice will depend on the reasons that motivated the rollover process. 5. RPKI-Router Protocol Withdrawals: At the expiration of the OLD certificate's validation, the RPKI relying parties around the globe will need to communicate to their router peers that the OLD certificate's public key is not longer valid (e.g., using the RPKI-Router Protocol described in [RFC6810]). A router's Weis, et al. Expires September 9, 2017 [Page 5] Internet-Draft BGPsec rollover March 2017 reaction to a message indicating withdrawal of a prefix in the RPKI-Router Protocol SHOULD include the removal of any RIB entry that includes a BGPsec attribute signed with that key and the generation of the correspondent BGP WITHDRAWALs (either implicit or explicit). The proposed rollover mechanism will depend on the existence of an automatic provisioning process for BGPsec certificates. It will require a staging mechanism based on the RPKI propagation time of around 24 hours, and it will generate BGPsec_Path attributes for all prefixes in the router been re-keyed. The first two steps (New Certificate Publication and Staging Period) may happen in advance of the rest of the process. This will allow a network operator to accelerate its subsequent key roll-over. When a new BGPsec certificate is generated without changing its key, steps 3 (Twilight) and 5 (RPKI-Router Protocol Withdrawals) SHOULD NOT be executed. 4. BGPsec key rollover as a measure against replays attacks in BGPsec There are two typical generic measures to mitigate replay attacks in any protocol: the addition of a timestamp or the addition of a serial number. However neither BGP nor BGPsec provide either measure. This section discusses the use of BGPsec Rollover as a measure to mitigate replay attacks. 4.1. BGPsec Replay attack window requirement In [RFC7353] Section 4.3, the need to limit the vulnerability to replay attacks is described. One important comment is that during a window of exposure, a replay attack is effective only in very specific circumstances: there is a downstream topology change that makes the signed AS path no longer current, and the topology change makes the replayed route preferable to the route associated with the new update. In particular, if there have been no topology change at all, then no security threat comes from a replay of a BGPsec_Path attribute because the signed information is still valid. The BGPsec Ops document [I-D.ietf-sidr-bgpsec-ops] gives some idea of requirements for the size of the BGPsec windows of exposure to replay attacks. It states that the requirement will be in the order of a day or longer. Weis, et al. Expires September 9, 2017 [Page 6] Internet-Draft BGPsec rollover March 2017 4.2. BGPsec key rollover as a mechanism to protect against replay attacks Since the window requirement is in the order of a day (as documented in [I-D.ietf-sidr-bgpsec-ops]) and the BGP speaker re-keying is the edge router of the origin AS, it is feasible for a BGPsec Rollover to mitigate replays. In this case it is important to complete the full process (i.e. the OLD and NEW certificate do not share the same key). By re-keying an AS is letting the BGPsec certificate validation time be a type of "timestamp" against replay attacks. However, the use of frequent key rollovers comes with an additional administrative cost and risks if the process fails. As documented before, re-keying should be supported by automatic tools and for the great majority of the Internet it will be done with good lead time to correct any risk. For a transit AS that also originates BGPsec_Path attributes for its own prefixes, the key rollover process may generate a large number of UPDATE messages (even the complete Default Free Zone or DFZ). For this reason, it is recommended that routers in a transit AS that also originate BGPsec_Path attributes be provisioned with two certificates: one to sign BGPsec_Path attributes in transit and a second one to sign an BGPsec_Path attribute for prefixes originated in its AS. Only the second certificate (for prefixes originated in its AS) should be rolled-over frequently as a means of limiting replay attack windows. The transit BGPsec certificate is expected to live longer than the origin BGPsec certificate. Advantage of Re-keying as replay attack protection mechanism: 1. All expiration policies are maintained in the RPKI 2. Much of the additional administrative cost is paid by the provider that wants to protect its infrastructure, as it bears the human cost of creating and initiating distribution of new router key pairs and router EE certificates. (It is true that the cost of relying parties will be affected by the new objects, but their responses should be completely automated or otherwise routine.) 3. The re-keying can be implemented in coordination with planned topology changes by either origin ASes or transit ASes (e.g., if an AS changes providers, it completes a BGP Rollover) Disadvantage of Re-keying as replay attack protection mechanism: 1. There is more administrative load due to frequent rollover, although how frequent is still not clear. Some initial ideas are found in [I-D.ietf-sidr-bgpsec-ops] Weis, et al. Expires September 9, 2017 [Page 7] Internet-Draft BGPsec rollover March 2017 2. The minimum window size is bounded by the propagation time for RPKI caches to obtain the new certificate and CRL (2x propagation time). If provisioning is done ahead of time, the minimum window size is reduced to 1x propagation time for the CRL. However, these bounds will be better understood when RPKI and RPs are well deployed. 3. Re-keying increases the dynamics and size of RPKI repository. 5. IANA Considerations There are no IANA considerations. This section may be removed upon publication. 6. Security Considerations Several possible reasons can cause routers participating in BGPsec to rollover their signing keys, which also has the effect of invalidating BGPsec_Path attributes signatures using the current signature verification key. Conventional key management operations my dicate a re-key (e.g.,key exposure, change of certificate attributes, rollover policy). BGPsec routers also may need to change their signing keys and associated certificate as an anti-replay protection. The BGPsec Rollover method allows for an expedient rollover process when router certificates are distributed through the RPKI, but without causing routing failures due to a receiving router not being able to validate a BGPsec_Path attribute created by a router that is the subject of the rollover. 7. Acknowledgements We would like to acknowledge Randy Bush, Sriram Kotikalapudi, Stephen Kent and Sandy Murphy. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. Weis, et al. Expires September 9, 2017 [Page 8] Internet-Draft BGPsec rollover March 2017 8.2. Informative References [I-D.ietf-sidr-bgpsec-ops] Bush, R., "BGPsec Operational Considerations", draft-ietf- sidr-bgpsec-ops-16 (work in progress), January 2017. [I-D.ietf-sidr-bgpsec-protocol] Lepinski, M. and K. Sriram, "BGPsec Protocol Specification", draft-ietf-sidr-bgpsec-protocol-22 (work in progress), January 2017. [I-D.ietf-sidr-rtr-keying] Bush, R., Turner, S., and K. Patel, "Router Keying for BGPsec", draft-ietf-sidr-rtr-keying-12 (work in progress), June 2016. [RFC6489] Huston, G., Michaelson, G., and S. Kent, "Certification Authority (CA) Key Rollover in the Resource Public Key Infrastructure (RPKI)", BCP 174, RFC 6489, DOI 10.17487/RFC6489, February 2012, <http://www.rfc-editor.org/info/rfc6489>. [RFC6810] Bush, R. and R. Austein, "The Resource Public Key Infrastructure (RPKI) to Router Protocol", RFC 6810, DOI 10.17487/RFC6810, January 2013, <http://www.rfc-editor.org/info/rfc6810>. [RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, October 2013, <http://www.rfc-editor.org/info/rfc7030>. [RFC7353] Bellovin, S., Bush, R., and D. Ward, "Security Requirements for BGP Path Validation", RFC 7353, DOI 10.17487/RFC7353, August 2014, <http://www.rfc-editor.org/info/rfc7353>. Authors' Addresses Brian Weis Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 CA Email: firstname.lastname@example.org Weis, et al. Expires September 9, 2017 [Page 9] Internet-Draft BGPsec rollover March 2017 Roque Gagliano Cisco Systems Avenue des Uttins 5 Rolle, VD 1180 Switzerland Email: email@example.com Keyur Patel Arrcus, Inc. Email: firstname.lastname@example.org Weis, et al. Expires September 9, 2017 [Page 10]