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Versions: (draft-rogaglia-sidr-bgpsec-rollover) 00 01 02 03 04 05 06 draft-ietf-sidrops-bgpsec-rollover

Network Working Group                                        R. Gagliano
Internet-Draft                                                  K. Patel
Intended status: Standards Track                                 B. Weis
Expires: April 25, 2013                                    Cisco Systems
                                                        October 22, 2012


       BGPSEC router key rollover as an alternative to beaconing
                   draft-ietf-sidr-bgpsec-rollover-01

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).  This document
   provides general recommendations for that process and specifies how
   this process is used to control BGPSEC's window of exposure to replay
   attacks.

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 April 25, 2013.

Copyright Notice

   Copyright (c) 2012 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
   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



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   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  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Key rollover in BGPSEC . . . . . . . . . . . . . . . . . . . .  5
     3.1.  A proposed process for BGPSEC key rollover . . . . . . . .  5
   4.  BGPSEC key rollover as a measure against replays attacks
       in BGPSEC  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  BGPSEC Replay attack window requirement  . . . . . . . . .  8
     4.2.  BGPSEC key rollover as a mechanism to protect against
           replay attacks . . . . . . . . . . . . . . . . . . . . . .  8
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14




























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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 that
   Certificate Practice Statements (CPS) documents MAY reference.

   When a router receives (or creates depending of the key provisioning
   mechanism to be selected) a new key pair, this key pair will be used
   to sign new BGP UPDATE messages that are originated or that transit
   through the BGP speaker.  Additionally, the BGP speaker MUST refresh
   its outbound BGP UPDATE messages to update its respective BGPSEC
   attribute by including the correspondent signature performed with the
   new key.  When the rollover process finishes, the old BGPSEC
   certificate (and its key) will not longer be valid and thus any BGP
   UPDATE that includes a BGPSEC attribute with a signature performed by
   the old key will be invalid.  Consequently, if the router do not
   refresh its outbound BGP UPDATE messages, routing information may be
   lost after the rollover process is finished.

   As a key rollover process invalidates BGP UPDATE messages signed with
   the old key, frequent key rollover processes could be used to control
   BGPSEC's window of exposure to replay attacks as required by
   [I-D.ietf-sidr-bgpsec-reqs].  This document explores the operational
   environment to 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.

   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 should be dependent of 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 will be in place.  (A
   possible provisioning mechanism is the Enrollment over Secure
   Transport (EST) [I-D.ietf-pkix-est]).  That protocol 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:

   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
       this process will vary as they depend on whether the keys are
       assigned per-BGP speaker or shared, whether the keys are



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       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 BGP UPDATES just as in the typical operation
       of refreshing out-bound BGP polices.  This operation may generate
       a great number of BGP UPDATE messages (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).

   The proposed rollover mechanism will depend on the existence of an



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   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 BGP UPDATES 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.  Currently BGPSEC offers a timestamp (expiration time) as a
   protection against re-play attacks of BGPSEC attributes.  The process
   requires all BGP Speakers that originate a BGP UPDATE to re-advertise
   ("beacon") the message before it expires.  This requirement changes a
   long standing BGP operational practice and the community has been
   searching for alternatives.

4.1.  BGPSEC Replay attack window requirement

   In [I-D.ietf-sidr-bgpsec-reqs] 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, no security threat comes from a replay of a BGP
   UPDATE message (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

   The question we would like to ask is: can the key rollover process
   earlier described provide a similar protection against replay attacks
   without the need for beaconing?

   The answer is that YES when the window requirement is in the order of
   days and the BGP speaker re-keying is the edge router of the origin
   AS and the full process is completed (i.e. the OLD and NEW
   certificate do not share the same key).  By using re-keying, you are
   letting the BGPSEC certificate validation time as your 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 BGP UPDATES for its own
   prefixes, the key rollover process may generate a large number of



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   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 BGP UPDATES in transit
   and a second one to sign BGP UPDATE 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 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.  Does not require beaconing

   2.  All expiration policies are maintained in RPKI

   3.  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)

   4.  Can be implemented in coordination with planned topology changes
       by either origin ASes or transit ASes (if I am changing
       providers, I rollover)

   5.  Eliminates the discussion on who has the authority over the
       expiration time

   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

   No security considerations.
















































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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-pkix-cmc-serverkeygeneration]
              Schaad, J., Timmel, P., and S. Turner, "CMC Extensions:
              Server Key Generation",
              draft-ietf-pkix-cmc-serverkeygeneration-00 (work in
              progress), January 2012.

   [I-D.ietf-pkix-est]
              Pritikin, M., Yee, P., and D. Harkins, "Enrollment over
              Secure Transport", draft-ietf-pkix-est-02 (work in
              progress), July 2012.

   [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-reqs]
              Bellovin, S., Bush, R., and D. Ward, "Security
              Requirements for BGP Path Validation",
              draft-ietf-sidr-bgpsec-reqs-03 (work in progress),
              March 2012.

   [I-D.ietf-sidr-rtr-keying]
              Turner, S., Patel, K., and R. Bush, "Router Keying for
              BGPsec", draft-ietf-sidr-rtr-keying-00 (work in progress),
              May 2012.












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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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