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


   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

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   provisions of BCP 78 and BCP 79.

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   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
   ( in effect on the date of

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   publication of this document.  Please review these documents
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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",
   "OPTIONAL" in this document are to be interpreted as described in

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

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   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.

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   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

   BGPsec emergency rollover  Some special circumstances (such as a
         compromised key) may require the replacement of a BGPsec

   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

   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

   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

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       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

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       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.

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4.2.  BGPsec key rollover as a mechanism to protect against replay

   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

   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]

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   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

   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

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

   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,

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8.2.  Informative References

              Bush, R., "BGPsec Operational Considerations", draft-ietf-
              sidr-bgpsec-ops-16 (work in progress), January 2017.

              Lepinski, M. and K. Sriram, "BGPsec Protocol
              Specification", draft-ietf-sidr-bgpsec-protocol-22 (work
              in progress), January 2017.

              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,

   [RFC6810]  Bush, R. and R. Austein, "The Resource Public Key
              Infrastructure (RPKI) to Router Protocol", RFC 6810,
              DOI 10.17487/RFC6810, January 2013,

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,

   [RFC7353]  Bellovin, S., Bush, R., and D. Ward, "Security
              Requirements for BGP Path Validation", RFC 7353,
              DOI 10.17487/RFC7353, August 2014,

Authors' Addresses

   Brian Weis
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134


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   Roque Gagliano
   Cisco Systems
   Avenue des Uttins 5
   Rolle, VD  1180


   Keyur Patel
   Arrcus, Inc.


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