RPKI Certificate Tree Validation by a Relying Party Tool
draft-ietf-sidr-rpki-tree-validation-00

SIDR                                                        O. Muravskiy
Internet-Draft                                            T. Bruijnzeels
Intended status: Informational                                  RIPE NCC
Expires: September 22, 2016                               March 21, 2016

        RPKI Certificate Tree Validation by a Relying Party Tool
                draft-ietf-sidr-rpki-tree-validation-00

Abstract

   This document currently describes the approach to validate the
   content of the RPKI certificate tree, as used by the RIPE NCC RPKI
   Validator.  This approach is independent of a particular object
   retrieval mechanism.  This allows it to be used with repositories
   available over the rsync protocol, the RPKI Repository Delta
   Protocol, and repositories that use a mix of both.

   This algorithm does not rely on content of repository directories,
   but uses the Authority Key Identifier (AKI) field of a manifest and a
   certificate revocation list (CRL) objects to discover manifest and
   CRL objects issued by a particular Certificate Authority (CA).  It
   further uses the hashes of manifest entries to discover other objects
   issued by the CA.

   If the working group finds that algorithm outlined here is useful for
   other implementations, we may either update future revisions of this
   document to be less specific to the RIPE NCC RPKI Validator
   implementation, or we may use this document as a starting point of a
   generic validation document and keep this as a detailed description
   of the actual RIPE NCC RPKI Validator implementation.

Status of This Memo

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   This Internet-Draft will expire on September 22, 2016.

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Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Top-down Validation of a Single Trust Anchor Certificate Tree   3
     2.1.  Fetching the Trust Anchor Certificate Using the Trust
           Anchor Locator  . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Resource Certificate Validation . . . . . . . . . . . . .   4
       2.2.1.  Finding most recent valid manifest and CRL  . . . . .   5
       2.2.2.  Manifest entries validation . . . . . . . . . . . . .   6
     2.3.  Object Store Cleanup  . . . . . . . . . . . . . . . . . .   6
   3.  Remote Objects Fetcher  . . . . . . . . . . . . . . . . . . .   6
     3.1.  Fetcher Operations  . . . . . . . . . . . . . . . . . . .   7
       3.1.1.  Fetch repository objects  . . . . . . . . . . . . . .   7
       3.1.2.  Fetch single repository object  . . . . . . . . . . .   7
   4.  Local Object Store  . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Store Operations  . . . . . . . . . . . . . . . . . . . .   8
       4.1.1.  Store Repository Object . . . . . . . . . . . . . . .   8
       4.1.2.  Update object's last fetch time . . . . . . . . . . .   8
       4.1.3.  Get objects by hash . . . . . . . . . . . . . . . . .   8
       4.1.4.  Get certificate objects by URI  . . . . . . . . . . .   8
       4.1.5.  Get manifest objects by AKI . . . . . . . . . . . . .   8
       4.1.6.  Delete objects for URI  . . . . . . . . . . . . . . .   8
       4.1.7.  Delete outdated objects . . . . . . . . . . . . . . .   8
       4.1.8.  Update object's validation time . . . . . . . . . . .   9
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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1.  Introduction

   In order to use information published in RPKI repositories, Relying
   Parties (RP) need to retrieve and validate the content of
   certificates, CRLs, and other RPKI signed objects.  To validate a
   particular object, one must ensure that all certificates in the
   certificate chain up to the Trust Anchor (TA) are valid.  Therefore
   the validation of a certificate tree is usually performed top-down,
   starting from the TA certificate and descending down the certificate
   chain, validating every encountered certificate and its products.
   The result of this process is a list of all encountered RPKI objects
   with a validity status attached to each of them.  These results may
   later be used by a Relying Party in taking routing decisions, etc.

   Traditionally RPKI data is made available to RPs through the
   repositories [RFC6481] accessible over rsync protocol.  Relying
   parties are advised to keep a local copy of repository data, and
   perform regular updates of this copy from the repository (Section 5
   of[RFC6481]).  The RPKI Repository Delta Protocol
   [I-D.ietf-sidr-delta-protocol] introduces another method to fetch
   repository data and keep the local copy up to date with the
   repository.

   This document describes how a Relying Party tool could discover RPKI
   objects to download, build certificate path, and validate RPKI
   objects, independently from what repository access protocol is used.
   To achieve this, it puts downloaded RPKI objects in an object store,
   where objects could be found by their URI, hash of their content,
   value of the object's AKI field, or combination of these.  It also
   keeps track of download and validation time for every object, to
   perform cleanups of the local copy.

2.  Top-down Validation of a Single Trust Anchor Certificate Tree

   The validation of a Trust Anchor (TA) certificate tree starts from
   its TA certificate.  To retrieve the TA certificate, a Trust Anchor
   Locator (TAL) object is used, as described in Section 2.1.

   If the TA certificate is retrieved, it is validated according to the
   Section 7 of [RFC6487] and Section 2.2 of [RFC7730].

   Then the TA certificate and all its subordinate objects are validated
   as described in Section 2.2.

   For all repository objects that were validated during this validation
   run, their validation timestamp is updated in an object store (see
   Section 4.1.8).

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   Outdated objects are removed from the store as described in
   Section 2.3.  This completes the validation of the TA certificate
   tree.

2.1.  Fetching the Trust Anchor Certificate Using the Trust Anchor
      Locator

   The following steps are performed in order to fetch the Trust Anchor
   Certificate:

   o  (Optional) If the Trust Anchor Locator contains a "prefetch.uris"
      field, pass the URIs contained there to the fetcher (see
      Section 3.1.1).  (This field is a non-standard extension to the
      TAL format supported by the RIPE NCC Validator.  It helps fetching
      non-hierarchical rsync repositories more efficiently.)

   o  Extract the TA certificate URI from the TAL's URI section (see
      Section 2.1 of[RFC7730]) and pass to the object fetcher
      (Section 3.1.2).

   o  Retrieve from the object store (see Section 4.1.4) all certificate
      objects, for which the URI matches the URI extracted from the TAL
      in the previous step, and the public key matches the
      subjectPublicKeyInfo field of the TAL (see Section 2.1 of
      [RFC7730]).

   o  If no, or more than one such objects are found, issue an error and
      stop validation process.  Otherwise, use that object as the Trust
      Anchor certificate.

2.2.  Resource Certificate Validation

   The following steps describe the validation of a single resource
   certificate:

   o  If both the caRepository (Section 4.8.8.1 of [RFC6487]), and the
      id-ad-rpkiNotify (Section 3.5 of [I-D.ietf-sidr-delta-protocol])
      SIA pointers are present in the given resource certificate, use a
      local policy to determine which pointer to use.  Extract the URI
      from the selected pointer and pass it to the object fetcher (see
      Section 3.1.1).

   o  For a given resource certificate, find its manifest and
      certificate revocation list (CRL), using the procedure described
      in Section 2.2.1.  If no such manifest and CRL could be found,
      issue an error and stop processing current certificate.

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   o  Compare the URI found in the given resource certificate's id-ad-
      rpkiManifest field (Section 4.8.8.1 of [RFC6487]) with the URI of
      the manifest found in the previous step.  If they are different,
      issue a warning.

   o  Perform manifest entries validation as described in Section 2.2.2.

   o  Validate all resource certificate objects found on the manifest,
      using the CRL object found on the manifest, according to Section 7
      of [RFC6487].

   o  Validate all ROA objects found on the manifest, using the CRL
      object found on the manifest, according to the Section 4 of
      [RFC6482].

   o  Validate all Ghostbusters Record objects found on the manifest,
      using the CRL object found on the manifest, according to the
      Section 7 of [RFC6493].

   o  For every valid resource certificate object found on the manifest,
      apply the procedure described in this section (Section 2.2),
      recursively, provided that this resource certificate (identified
      by its SKI) has not yet been validated during current repository
      validation run.

2.2.1.  Finding most recent valid manifest and CRL

   Fetch from the store (see Section 4.1.5) all objects of type
   manifest, whose certificate's AKI field matches the SKI of the
   current CA certificate.

   Find the manifest object with the highest manifestNumber field
   (Section 4.2.1 of [RFC6486]), for which all following conditions are
   met:

   o  There is only one entry in the manifest for which the store
      contains exactly one object of type CRL, whose hash matches the
      hash of the entry.

   o  The manifest's certificate AKI equals the above CRL's AKI

   o  The above CRL is a valid object according to Section 6.3 of
      [RFC5280]

   o  The manifest is a valid object according to Section 4.4 of
      [RFC6486], using the CRL found above

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   Report an error for every invalid manifest with the number higher
   than the number of the valid manifest.

2.2.2.  Manifest entries validation

   For every entry in the manifest object:

   o  Construct an entry's URI by appending the entry name to the
      current CA's publication point URI.

   o  Get all objects from the store whose hash attribute equals entry's
      hash (see Section 4.1.3).

   o  If no such objects found, issue an error.

   o  For every found object, compare its URI with the URI of the
      manifest entry.  If they do not match, issue a warning.

   o  If no objects with matching URI found, issue a warning.

   o  If some objects with non-matching URI found, issue a warning.

2.3.  Object Store Cleanup

   At the end of the TA tree validation the store cleanup is performed:

   o  Given all objects that were validated during the current
      validation run, remove from the store (Section 4.1.7) all objects
      whose URI attribute matches the URI of one of the validated
      objects, but the content's hash is different.

   o  Remove from the store all objects that were last validated more
      than 7 days ago.

   o  Remove from the store all objects that were downloaded more than 2
      hours ago and have never been used in a validation process.

   The time intervals used in the steps above are a matter of local
   policy.

3.  Remote Objects Fetcher

   The fetcher is responsible for downloading objects from remote
   repositories (described in Section 3 of [RFC6481]) using rsync
   protocol ([rsync]), or RPKI Repository Delta Protocol (RRDP)
   ([I-D.ietf-sidr-delta-protocol]).

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3.1.  Fetcher Operations

3.1.1.  Fetch repository objects

   This operation receives one parameter - a URI.  For rsync protocol
   this URI points to a directory in a remote repository.  For RRDP
   repository it points to the repository's notification file.

   The fetcher performs following steps:

   o  If the given URI has been downloaded recently (as specified by the
      local policy), skip all following steps.

   o  Download the remote objects using the URI provided (for an rsync
      repository use a recursive mode).

   o  For every new object that is downloaded, try to parse it as an
      object of specific RPKI type (certificate, manifest, CRL, ROA,
      Ghostbusters record), based on the object's filename extension
      (.cer, .mft, .crl, .roa, and .gbr, respectively), and perform
      basic RPKI object validation, as specified in [RFC6487] and
      [RFC6488].

   o  For every downloaded valid object, record it in the object store
      (Section 4.1.1), and set its last fetch time to the time it was
      downloaded (Section 4.1.2).

3.1.2.  Fetch single repository object

   This operation receives one parameter - a URI that points to an
   object in a remote repository.

   The fetcher performs following operations:

   o  If the given URI has been downloaded recently (as specified by the
      local policy), skip all following steps.

   o  Download the remote object using the URI provided.

   o  Try to parse the downloaded object as an object of a specific RPKI
      type (certificate, manifest, CRL, ROA, Ghostbusters record), based
      on the object's filename extension (.cer, .mft, .crl, .roa, and
      .gbr, respectively), and perform basic RPKI object validation, as
      specified in [RFC6487] and [RFC6488].

   o  If the downloaded object is not valid, issue an error and skip
      further steps.

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   o  Delete objects from the object store (Section 4.1.6) whose URI
      matches the URI given.

   o  Put validated object in the object store (Section 4.1.1), and set
      its last fetch time to the time it was downloaded (Section 4.1.2).

4.  Local Object Store

4.1.  Store Operations

4.1.1.  Store Repository Object

   Put given object in the store, along with its type, URI, hash, and
   AKI, if there is no record with the same hash and URI fields.

4.1.2.  Update object's last fetch time

   For all objects in the store whose URI matches the given URI, set the
   last fetch time attribute to the given timestamp.

4.1.3.  Get objects by hash

   Retrieve all objects from the store whose hash attribute matches the
   given hash.

4.1.4.  Get certificate objects by URI

   Retrieve from the store all objects of type certificate, whose URI
   attribute matches the given URI.

4.1.5.  Get manifest objects by AKI

   Retrieve from the store all objects of type manifest, whose AKI
   attribute matches the given AKI.

4.1.6.  Delete objects for URI

   For a given URI, delete all objects in the store with matching URI
   attribute.

4.1.7.  Delete outdated objects

   For a given URI and a list of hashes, delete all objects in the store
   with matching URI, whose hash attribute is not in the given list of
   hashes.

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4.1.8.  Update object's validation time

   For all objects in the store whose hash attribute matches the given
   hash, set the last validation time attribute to the given timestamp.

5.  Acknowledgements

   This document describes the algorithm as it is implemented by the
   software development team at the RIPE NCC.  The original idea behind
   it was outlined by Tim Bruijnzeels.  The authors would also like to
   acknowledge contributions by Carlos Martinez, Andy Newton, and Rob
   Austein.

6.  IANA Considerations

   This document has no actions for IANA.

7.  Security Considerations

   This algorithm uses the content of a manifest object to discover
   other objects issued by a particular CA.  It verifies that the
   manifest is located in the publication point designated in the CA
   Certificate.  However, if there are other (not enlisted in the
   manifest) objects located in that publication point directory, they
   will be ignored, even if their content is correct and they are issued
   by the same CA as the manifest.

   In contrast, objects whose content hash matches the hash listed in
   the manifest, but that are not located in the publication directory
   listed in their CA certificate, will be used in the validation
   process (although a warning will be issued in that case).

   The store cleanup procedure described in Section 2.3 tries to
   minimise removal and subsequent re-fetch of objects that are
   published in some repository but not used in the validation.  Once
   such objects are removed from the remote repository, they will be
   discarded from the local object store after a period of time
   specified by a local policy.  By generating an excessive amount of
   syntactically valid RPKI objects, a man-in-the-middle attack rendered
   between a validating tool and a repository could force an
   implementation to fetch and store those objects in the object store
   before they are being validated and discarded, leading to an out-of-
   memory or out-of-disk-space conditions, and, subsequently, a denial
   of service.

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8.  References

8.1.  Normative References

   [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, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC6481]  Huston, G., Loomans, R., and G. Michaelson, "A Profile for
              Resource Certificate Repository Structure", RFC 6481,
              DOI 10.17487/RFC6481, February 2012,
              <http://www.rfc-editor.org/info/rfc6481>.

   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482,
              DOI 10.17487/RFC6482, February 2012,
              <http://www.rfc-editor.org/info/rfc6482>.

   [RFC6486]  Austein, R., Huston, G., Kent, S., and M. Lepinski,
              "Manifests for the Resource Public Key Infrastructure
              (RPKI)", RFC 6486, DOI 10.17487/RFC6486, February 2012,
              <http://www.rfc-editor.org/info/rfc6486>.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,
              <http://www.rfc-editor.org/info/rfc6487>.

   [RFC6488]  Lepinski, M., Chi, A., and S. Kent, "Signed Object
              Template for the Resource Public Key Infrastructure
              (RPKI)", RFC 6488, DOI 10.17487/RFC6488, February 2012,
              <http://www.rfc-editor.org/info/rfc6488>.

   [RFC6493]  Bush, R., "The Resource Public Key Infrastructure (RPKI)
              Ghostbusters Record", RFC 6493, DOI 10.17487/RFC6493,
              February 2012, <http://www.rfc-editor.org/info/rfc6493>.

   [RFC7730]  Huston, G., Weiler, S., Michaelson, G., and S. Kent,
              "Resource Public Key Infrastructure (RPKI) Trust Anchor
              Locator", RFC 7730, DOI 10.17487/RFC7730, January 2016,
              <http://www.rfc-editor.org/info/rfc7730>.

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8.2.  Informative References

   [I-D.ietf-sidr-delta-protocol]
              Bruijnzeels, T., Muravskiy, O., Weber, B., Austein, R.,
              and D. Mandelberg, "RPKI Repository Delta Protocol",
              draft-ietf-sidr-delta-protocol-02 (work in progress),
              March 2016.

   [rsync]    "Rsync home page", <https://rsync.samba.org>.

Authors' Addresses

   Oleg Muravskiy
   RIPE NCC

   Email: oleg@ripe.net

   Tim Bruijnzeels
   RIPE NCC

   Email: tim@ripe.net

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