BGPSEC Router Certificate Rollover
draft-ietf-sidr-bgpsec-rollover-03

Network Working Group                                        R. Gagliano
Internet-Draft                                                  K. Patel
Intended status: Standards Track                                 B. Weis
Expires: September 7, 2015                                 Cisco Systems
                                                           March 6, 2015

                   BGPSEC Router Certificate Rollover
                   draft-ietf-sidr-bgpsec-rollover-03

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 pubic keys
   by BGPSEC routers.  This document provides general recommendations
   for that process, as well as describing reasons why the rollover of
   BGPSEC EE certificates might be necssary.

Status of this Memo

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   This Internet-Draft will expire on September 7, 2015.

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   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Key rollover in BGPSEC . . . . . . . . . . . . . . . . . . . .  6
     3.1.  A proposed process for BGPSEC key rollover . . . . . . . .  6
   4.  BGPSEC key rollover as a measure against replays attacks
       in BGPSEC  . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  BGPSEC Replay attack window requirement  . . . . . . . . .  9
     4.2.  BGPSEC key rollover as a mechanism to protect against
           replay attacks . . . . . . . . . . . . . . . . . . . . . .  9
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

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1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

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2.  Introduction

   In BGPSEC, a key rollover (or re-keying) is the process of changing a
   router's key pair (or pairs), issuing the corresponding new End-
   Entity 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 local policies at each network.
   This document provides general recommendations for that process.
   Certificate Practice Statements (CPS) documents MAY reference these
   recommendations.  This process is comceptually similar to the RPKI
   Key Rollover process defined in [RFC6489].

   When a router receives or creates a new key pair (depending on the
   key provisioning mechanism to be selected), this key pair will be
   used to sign new 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 lost after the rollover
   process is finished.  It is therefore extremely important that the
   BGPSEC router key rollover be performed such 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 protection against a replay attack,
   necessitating controlling BGPSEC's window of exposure to replay
   attacks.  The BGPsec rollver method in this document can be used to

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   achieve this goal.

   In [I-D.ietf-sidr-rtr-keying], the "operator-driven" method is
   introduced and it enables that a key pair could 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.

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3.  Key rollover in BGPSEC

   A BGPSEC EE certificate (as any X.509 certificate) will required a
   rollover process due to causes such as:

   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 continue to be propogated

   In most of these cases (probably excepting when the key has been
   compromised), it is possible to generate a new certificate without
   changing the key pair.  This practice simplifies the rollover process
   as the correspondent 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 the
   certificate key may be compromised.

3.1.  A proposed process for BGPSEC key rollover

   The BGPSEC key rollover process will be dependent on the key
   provisioning mechanisms that would be in place.  The key provisioning
   mechanisms for BGPSEC are not yet fully documented (see
   [I-D.ietf-sidr-rtr-keying] as a work in progress document).  We will
   assume that an automatic provisioning mechanism suchas EST will be in
   place.  The use of 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 possible process could be
   as follows.

   1.  New Certificate Pre-Publication: The first step in the rollover
       mechanism is to pre-publish the new public key in a new
       certificate.  In order to accomplish this goal, the new key pair
       and certificate will need to be generated and published at the
       appropriate RPKI repository publication point.  The details of

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       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 wether
       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 is not clear and will require
       experimental results from RPKI operations.  RPKI repository
       design documents mention a lower limit of 24 hours (NOTE: need
       reference only one I found is the ops document).  If rollovers
       will be done frequently and we want to avoid the stage period, an
       administrator can always provision two certificate for every
       router.  In this case when the rollover operation is needed, the
       relying parties around the globe would already have the new 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 hold 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.  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.  On the other
       side, the CA will just let the OLD certificate to expire and not
       revoke it.  This chose will depend on the reasons that motivated
       the rollover process.

   5.  RPKI-Router Protocol Withdrawals: Either due to the revocation of
       the OLD certificate or to the expiration of the OLD certificate's
       validation, the RPKI relying parties around the globe will need
       to communicate to their RTR peers that the OLD certificate's
       public key is not longer valid (rtr withdrawal message).  It is
       not documented yet what will be a router's reaction to a RTR
       withdrawal message but it 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).

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   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 24hours, and it will generate BGPsec_Path attributes for all
   prefixes in the router been re-keyed.

   The first two steps (New Certificate Pre-Publication and Staging
   Period) could happen ahead of time from the rest of the process as
   each network operators could prepare itself to accelerate a future
   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.

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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
   windows of exposure, a replay attack is effective only if there was a
   downstream topology change that makes the signed AS path not longer
   current.  In other words, if there have been no topology changes,
   then no security threat comes from a replay of a BGPsec_Path
   attribute (the signed information is still valid).

   The BGPSEC Ops document [I-D.ietf-sidr-bgpsec-ops] gives some ideas
   of requirements for the size of the BGPSEC windows of exposure to
   replay attacks.  At that document, it is stated that for the vast
   majority of the prefixes, the requirement will be in the order of
   days or weeks.  For a very small but critical fraction of the
   prefixes, the requirement may be in the order of hours.

4.2.  BGPSEC key rollover as a mechanism to protect against replay
      attacks

   Since the window requirement is in the order of days (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 mitigate.  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 sort 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 this scenario been
   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

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   means of limiting replay attach windows.  The transit BGPSEC
   certificate is expected to be longer living than the origin BGPSEC
   certificate.

   Advantage of Re-keying as replay attack protection mechanism:

   1.  All expiration policies are maintained in RPKI

   2.  Most of the additional administrative cost is paid by the
       provider that wants to protect its infrastructure (RP load will
       increase as there is a need to validate more BGPSEC certificates)

   3.  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.  More administrative load due to frequent rollover, although how
       frequent is still not clear.  Some initial ideas in
       [I-D.ietf-sidr-bgpsec-ops]

   2.  Minimum window size bounded by RPKI propagation time to RPKI
       caches for new certificate and CRL (2x propagation time).  If
       pre-provisioning done ahead of time the minimum windows size is
       reduced (to 1x propagation time for the CRL).  However, more
       experimentation is needed when RPKI and RPs are more massively
       deployed.

   3.  Increases dynamics and size of RPKI repository.

   4.  More load on RPKI caches, but they are meant to do this work.

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5.  IANA Considerations

   No IANA considerations

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6.  Security Considerations

   Several possible reasons can cause routers participating in BGPSEC to
   replace rollover their signing keys and/or signatures containing
   their current signature verification key.  Some reasons are due to
   the usual key management operations reasons (e.g.,key exposure,
   change of certificate attributes, due to policy).  However 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.

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7.  Acknowledgements

   We would like to acknowledge Randy Bush, Sriram Kotikalapudi, Stephen
   Kent and Sandy Murphy.

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8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6489]  Huston, G., Michaelson, G., and S. Kent, "Certification
              Authority (CA) Key Rollover in the Resource Public Key
              Infrastructure (RPKI)", BCP 174, RFC 6489, February 2012.

8.2.  Informative References

   [I-D.ietf-sidr-bgpsec-ops]
              Bush, R., "BGPsec Operational Considerations",
              draft-ietf-sidr-bgpsec-ops-05 (work in progress),
              May 2012.

   [I-D.ietf-sidr-bgpsec-protocol]
              Lepinski, M., "BGPsec Protocol Specification",
              draft-ietf-sidr-bgpsec-protocol-11 (work in progress),
              January 2015.

   [I-D.ietf-sidr-rtr-keying]
              Patel, K. and R. Bush, "Router Keying for BGPsec",
              draft-ietf-sidr-rtr-keying-08 (work in progress),
              January 2015.

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

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

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Authors' Addresses

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

   Email: rogaglia@cisco.com

   Keyur Patel
   Cisco Systems
   170 W. Tasman Driv
   San Jose, CA  95134
   CA

   Email: keyupate@cisco.com

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

   Email: bew@cisco.com

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