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Versions: 00 01 draft-ietf-sidr-rpki-validation-reconsidered

Network Working Group                                          G. Huston
Internet-Draft                                             G. Michaelson
Intended status: Informational                                     APNIC
Expires: August 13, 2014                                February 9, 2014


                      RPKI Validation Reconsidered
                  draft-huston-rpki-validation-01.txt

Abstract

   This document reviews the certificate validation procedure specified
   in RFC6487 and highlights aspects of operational management of
   certificates in the RPKI in response to the movement of resources
   across registries, and the associated actions of Certification
   Authorities to maintain certification of resources during this
   movement.  The document describes an alternative validation procedure
   that reduces the operational impact of certificate management during
   resource movement.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on August 13, 2014.

Copyright Notice

   Copyright (c) 2014 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
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   (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.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Operational Considerations . . . . . . . . . . . . . . . . . .  4
   3.  A Specific Resource RPKI Certificate Validation Process  . . .  6
     3.1.  Resource Transfers and Specific Resource Certificate
           Validation . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.2.  A Specification of Specific Resource Validation  . . . . .  8
   4.  Local Repository Cache Maintenance . . . . . . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12



































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1.  Introduction

   This document reviews the certificate validation procedure specified
   in [RFC6487] and highlights aspects of operational management of
   certificates in the RPKI in response to the movement of resources
   across registries, and the associated actions of Certification
   Authorities to maintain certification of resources during this
   movement.  The document describes an alternative validation procedure
   that reduces the operational impact of certificate management during
   resource movement.  The alternative validation procedure also offers
   a higher level of robustness in the face of resource inconsistencies
   in a putative certificate validation path.

   As currently defined in section 7.2 of [RFC6487], validation of PKIX
   certificates that conform to the RPKI profile relies on the use of a
   path validation process where each certificate in the validation path
   is required to meet the certificate validation criteria.  This can be
   considered to be a recursive validation process where, in the context
   of an ordered sequence of certificates, as defined by common Issuer
   and Subject Name pairs, a certificate is defined as valid if it
   satisfies basic validation criteria relating to the syntactic
   correctness, currency of validity dates and similar properties of the
   certificate itself, as described in [RFC5280], and also that it
   satisfies certain additional criteria with respect to the previous
   certificate in the sequence, and that this previous certificate is
   itself a valid certificate using the same criteria.  This definition
   applies recursively to all certificates in the sequence apart from
   the initial sequence element, which is required to be a Trust Anchor.

   For RPKI certificates, the additional criteria relating to the
   previous certificate in this sequence is that the certificate's
   number resource set, as defined in [RFC3779], is "encompassed" by the
   number resource set contained in the previous certificate.

   Because [RFC6487] validation demands that all resources in a
   certificate be valid under the parent (and recursively, to the root),
   a digitally signed attestation, such as a Route Origin Authorization
   (ROA) object [RFC6482], which refers only to a subset of RFC3779-
   specified resources from that certificate chain can be concluded to
   be invalid, but not by virtue of the relationship between the RFC3779
   extensions of the certificates on the putative certificate validation
   path and the resources in the ROA, but by other resources described
   in these certificates where the "encompassing" relationship of the
   resources does not hold.  Any such invalidity along the certificate
   validation path can cause this outcome, not just at the immediate
   parent of the end entity certificate that attests to the key used to
   sign the ROA.




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   For example, in the certificate sequence:

     Certificate 1:
       Issuer A, Subject B, Resources 192.0.2.0/24, AS64496-AS64500

     Certificate 2:
       Issuer B, Subject C, Resources 192.0.2.0/24/24, AS64496-AS64511

     Certificate 3:
       Issuer C, Subject D, Resources 192.0.2.0/24

   Certificate 3 is considered to be an invalid certificate, because the
   resources in Certificate 2 are not encompassed by the resources in
   Certificate 1, by virtue of certificate 2 holding the resources of
   the range AS64501 - AS64511 in this RFC3779 resource extension.
   Obviously, these Autonomous Systems numbers are not related to the
   IPv4 resources contained in Certificate 3.


2.  Operational Considerations

   There are two areas of operational concern with the current RPKI
   validation definition.

   The first is that of the robustness of the operatinal management
   procesures in the issuance of certificates.  If a subordinate CA
   issues a certificate that contains an Internet Number Resource (INR)
   collection that is not either exactly equal to, or a strict subset
   of, its parent CA, then this issued certificate, and all subordinate
   certificates of this issued certificate are invalid.  These
   certificates are not only defined as invalid when being considered to
   validate an INR that is not in the parent CA certificate, but are
   defined as invalid for all INRs in the certificate.  This creates a
   degree of operational fragility in the issuance of certificates, as
   all CA's are now required to exercise extreme care in the issuance
   and reissuance of certificates that they do not overclaim on the
   resources described in the parent CA, as the consequences of an
   operational lapse or oversight implies that all the subordinate
   certificates from the point of mismatch are invalid.  It would be
   preferred if the consequences of such an operational lapse were
   limited in scope to the specific INRs that formed the mismatch,
   rather than including the sntire set of INRs within the scope of
   damage from this oversight.

   The second operational consideration described here relates to the
   situation where a registry withdraws a resource from the current
   holder, and the resource to transferred to another registry, to be
   registered to a new holder in that registry.  The reason why this is



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   a consideration in operational deployments of the RPKI lies in the
   movement of the "home" registry of number resources during cases of
   mergers, acquisitions, business re-alignments, and resource transfers
   and the desire to ensure that during this movement all other
   resources can continue to be validated.

   If the original registry's certification actions are simply to issue
   a new certificate for the current holder with a reduced resource set,
   and to revoke the original certificate, then there is a distinct
   possibility of encountering the situation illustrated by the example
   in the previous section.  This is a result of an operational process
   for certificate issuance by the parent CA being de-coupled from the
   certificate operations of child CA.

   This de-coupled operation of CAs introduces a risk of unintended
   third party damage: since a CA certificate can refer to holdings
   which relate to two or more unrelated subordinate certificates, if
   this CA certificate becomes invalid due to the reduction in the
   resources allocated to this CA relating to one subordinate resource
   set, all other subordinate certificates are invalid until the CA
   certificate is reissued with a reduced resource set.

   In the above example, all subordinate certificates issued by CA C are
   invalid until CA B issues a new certificate for CA C with a reduced
   resource set.

   At the lover levels of the RPKI hierarchy the resource sets affected
   by such movements of resources may not encompass significantly large
   pools of resources.  However, as one ascends through this hierarchy
   towards the apex, the larger the resource set that is going to be
   affected by a period of invalidity by virtue of such uncoordinated
   certificate management actions.  In the case of a Regional Internet
   Registry (RIR) or National Internet Registry (NIR), the potential
   risk arising from uncoordinated certification actions relating to a
   transfer of resources is that the entire set of subordinate
   certificates that refer to resources administered by the RIR or the
   NIR cannot be validated during this period.

   Avoiding such situations requires that CA's adhere to a very specific
   ordering of certificate issuance.  In this framework, the common
   registry CA that describes (directly or indirectly) the resources
   being shifted from one registry to the other, and also contains in
   subordinate certificates (direct or indirect) the certificates for
   both registries who are parties to the resource transfer has to
   coordinate a specific sequence of actions.

   This common registry CA has to first issue a new certificate towards
   the "receiving" registry that adds to the RFC3779 extension resource



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   set the specific resource being transferred into this receiving
   registry.  The common registry CA then has to wait until all
   registries in the subordinate certificate chain to the receiving
   registry have also performed a similar issuance of new certificates,
   and in each case a registry must await the issuance of the immediate
   superior certificate with the augmented resource set before it, in
   turn, can issue its own augmented certificate to its subordinate CA.
   This is a "top down" issuance sequence."

   It is possible for the common registry to issue a certificate to the
   "sending" registry with the reduced resource set at any time, but it
   should not revoke the previously issued certificate, nor overwrite
   this previously issued certificate in its repository publication
   point without specific coordination.  Only when the common registry
   is assured that the top down certificate issuance process to the
   receiving registry CA chain has been completed can the common
   registry commence the revocation of the original certificate for the
   sending registry, However, it should not so until it is assured that
   the immediate subordinate registry CA in the path to the sending
   registry has issued a certificate with a reduced resource set, and so
   on.  This implies that on the sending side the certificate issuance
   and revocation is a "bottom up" process.

   If this process is not carefully followed, then the risk is that some
   or all or the subordinate certificates of this common registry CA
   will be unable to be validated until the entire process of
   certificate issuance and revocation has been completed.  While this
   sequenced process is intended to preserve validity of certificates in
   the RPKI, it is a complex and operationally cumbersome process.

   The underlying consideration here is that the operational
   coordination of these certificate issuance and revocation actions to
   effect a smooth resource transfer across registries is mandated by
   the nature of the certificate validation process described in
   [RFC6487].


3.  A Specific Resource RPKI Certificate Validation Process

   The question considered here is: Is there an alternate definition of
   RPKI certificate validity that could remove the requirement for such
   careful orchestration of certification actions across the RPKI to
   support resource transfers?

   The general definition of certificate validity as defined in
   [RFC5280] assumes a validation question relating to the relying
   party's (RP's) level of trust in a subject's signed material, given
   knowledge of a subject's name, the subject's public key, the RP's



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   chosen trust anchor(s) and an overall PKI to define the domain of
   discourse.

   The validation question assumed by the [RFC6487] RPKI certificate
   validation process relates to a RP's level of trust in the
   combination of some signed material, a certificate that attests to
   the public key used to sign this material and the set of all number
   resources that have been assigned or allocated to the subject of the
   certificate, given knowledge of the certificate, the RP's chosen
   trust anchor(s), the RPKI, and the application of the same test
   applied to the superior certificate in the RPKI hierarchy, and so on
   to a Trust Anchor.

   There is a alternative certificate validation procedure that starts
   with an attestation containing the subject's signed material and an
   explicit enumeration of a set of number resources.  The associated
   validation question relates to whether a RPKI validation process can
   attest to the validity of a subject's signed attestation relating to
   a particular set of number resources, rather than a signed
   attestation relating to all number resources held by this subject.
   We will term this alternate certificate validation process "specific
   resource" validation.

   If the certificate validation procedure is specifically restricted to
   a question of ascertaining the validity of a particular set of number
   resources in the context of the RPKI, the RPKI validation procedure
   need not be as strict as a recursive "encompassing" condition for the
   resources contained in each pair of certificates in the validation
   path.  It would be sufficient in the context of this "specific
   resource" validation procedure to require only that each certificate
   in the validation path has a number resource extension that
   "encompasses" the specific resources described in the original
   validation question.  Rather than a validation test for all possible
   questions, this is a specific validation question in the context of
   specific resources.

   This validation question can be informally described as: Given a
   certificate and a given resource set, is there an Issuer-Subject
   ordered sequence of certificates from a Trust Anchor to the
   certificate being validated, where each certificate on this sequence
   is well-formed, not revoked by a valid CRL, where the certificate's
   lifetimes are valid, and where the RFC3779 resource extension in the
   certificate encompass the given resource set?

   In the example from Section 1, using a this alternate certificate
   validation process, a validation question of certificate 3 and the
   resource 10.0.1.0/24, the validation outcome would be positive, in
   that certificates 1, 2 and 3 all encompass the specific resource



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   10.0.1.0/24, assuming that the certificates are valid in all other
   respects.

3.1.  Resource Transfers and Specific Resource Certificate Validation

   When considering the transfer of resources across registries, and the
   associated certification actions, then if the validation process was
   one of "specific resource" validation, then there is no requirement
   for synchronized orchestration of the process of certificate issuance
   and revocation by the CAs involved in this transfer in order to
   preserve the validity of resources described in these certificates.

   Along the chain of the "sending" registry CA hierarchy each registry
   CA can issue a certificate with a reduced resource set that removes
   the resource being transferred, and revoke the previously issued
   certificate without regard to the specific timing of similar actions
   by either it's superior or its subordinate registry CA.

   Similarly, in the "receiving" registry hierarchy each CA can issue a
   certificate with an augmented resource set that includes the resource
   being transferred without particular regard to the timing of similar
   actions by the other superior or subordinate registry CAs.

   Validation questions relating to the migrating resource made against
   certificates on the "sending registry" will return an invalid outcome
   as soon as any registry CA in this chain has performed revocation of
   the original certificate.  Validation questions relating to the
   migrating resource made against certificates on the "receiving
   registry" will return an valid outcome only when all the registries
   in this chain have performed certificate re-issuance and included the
   resource in the new certificate.

   Critically, at all times validation questions relating to any other
   resource using the "specific resource" validation approach will
   return the same outcomes throughout this issuance and revocation
   process.  This "specific resource" validation process engenders a
   more robust outcome in RPKI certificate management.  Validation
   questions relating to resources which are not being transferred from
   one registry to another cannot be compromised by any failure to
   adhere to a strict process of issuance and revocation relating to the
   certification of the resources being transferred.

3.2.  A Specification of Specific Resource Validation

   The following is a amended specification of certificate validation as
   described in [RFC6487] that describes the proposed "specific
   resource" certificate validation process.




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   Validation of signed resource data using a target resource
   certificate and a specific set of number resources consists of
   verifying that the digital signature of the signed resource data is
   valid, using the public key of the target resource certificate, and
   also validating the resource certificate in the context of the RPKI,
   using the path validation process.  This path validation process
   verifies, among other things, that a prospective certification path
   (a sequence of n certificates) satisfies the following conditions:




      1.  for all 'x' in {1, ..., n-1}, the Subject of certificate 'x'
          is the Issuer of certificate ('x' + 1);


      2.  certificate '1' is issued by a trust anchor;


      3.  certificate 'n' is the certificate to be validated; and


      4.  for all 'x' in {1, ..., n}, certificate 'x' is valid.

   Certificate validation entails verifying that all of the following
   conditions hold, in addition to the Certification Path Validation
   criteria specified in Section 6 of [RFC5280]:




      1.  The certificate can be verified using the Issuer's public key
          and the signature algorithm


      2.  The current time lies within the certificate's Validity From
          and To values.


      3.  The certificate contains all fields that MUST be present, as
          defined by this specification, and contains values for
          selected fields that are defined as allowable values by this
          specification.


      4.  No field, or field value, that this specification defines as
          MUST NOT be present is used in the certificate.




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      5.  The Issuer has not revoked the certificate.  A revoked
          certificate is identified by the certificate's serial number
          being listed on the Issuer's current CRL, as identified by the
          CRLDP of the certificate, the CRL is itself valid, and the
          public key used to verify the signature on the CRL is the same
          public key used to verify the certificate itself.


      6.  The resource extension data contained in this certificate
          "encompasses" the entirety of the resources in the specific
          resource set.


      7.  The Certification Path originates with a certificate issued by
          a trust anchor, and there exists a signing chain across the
          Certification Path where the Subject of Certificate 'x' in the
          Certification Path matches the Issuer in Certificate 'x + 1'
          in the Certification Path, and the public key in Certificate
          'x' can verify the signature value in Certificate 'x+1'.

   A certificate validation algorithm MAY perform these tests in any
   chosen order.


4.  Local Repository Cache Maintenance

   This change in the validation process would have some impact on the
   operation of a local cache of validated RPKI certificates.  Given
   that the validation process requires the specification of a specific
   resource set, it would appear that it would not be possible to
   validate an RPKI certificate without also specifying a specific
   resource set.

   However, using a top-down validation process, and an additional local
   data structure associated with each locally held validated RPKI
   certificate, it is possible to maintain a local cache of validated
   certificates, and the set of valid and invalid resources for each
   certificate.

   The additional data structures are the certificate's validated and
   invalidated resource set.  These sets are defined as follows:

   o  If the certificate is used as a Trust Anchor, then the local
      validated resource set is copied from the certificate's RFC3779
      resource set.  There is no invalid resource set.

   o  Otherwise, the certificate's local validated resource set is
      defined as the intersection of this certificate's RFC3779 resource



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      set and the parent certificate's local validated resource set.
      The certificate's invalid resource set is the difference between
      this set and the certificate's RFC3779 resource set.

   If the certificate's validated resource set is empty then the
   certificate is not valid.

   If the invalid resource set is not empty, then any resources that are
   contained in this invalid resource set cannot be valid by virtue of
   this certificate.

   In all operations on the local repository cache, local applications
   should use the certificate's local validated resource set in place of
   the resources described in the certificate's RFC3779 extension.

   The invalid resource set can be used as a diagnostic aide in local
   cache management.


5.  Security Considerations

   The Security Considerations of [RFC6487] apply to the validation
   procedure described here.


6.  IANA Considerations

   No updates to the registries are suggested by this document.


7.  Acknowledgements

   TBA.


8.  References

8.1.  Normative References

   [RFC3779]  Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
              Addresses and AS Identifiers", RFC 3779, June 2004.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for



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              X.509 PKIX Resource Certificates", RFC 6487,
              February 2012.

8.2.  Informative References

   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482, February 2012.


Authors' Addresses

   Geoff Huston
   Asia Pacific Network Information Centre (APNIC)
   6 Cordelia St
   South Brisbane, QLD  4101
   Australia

   Phone: +61 7 3858 3100
   Email: gih@apnic.net


   George Michaelson
   Asia Pacific Network Information Centre (APNIC)
   6 Cordelia St
   South Brisbane, QLD  4101
   Australia

   Phone: +61 7 3858 3100
   Email: ggm@apnic.net






















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