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Versions: (draft-huston-sidr-repos-struct) 00 01 03 04 05 06 07 08 09 RFC 6481

Individual Submission                                          G. Huston
Internet-Draft                                                R. Loomans
Intended status: Best Current                              G. Michaelson
Practice                                                           APNIC
Expires: February 8, 2009                                 August 7, 2008


        A Profile for Resource Certificate Repository Structure
                  draft-ietf-sidr-repos-struct-00.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This document defines a profile for the structure of repositories
   that contain X.509 / PKIX Resource Certificates, Certificate
   Revocation Lists and signed objects.  This profile contains the
   proposed object naming scheme, the contents of repository publication
   points, the contents of publication point manifests and a possible
   internal structure of a Repository Cache that is intended to
   facilitate synchronization across a distributed collection of



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   repositories and facilitate certificate path construction.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  RPKI Repository Publication Point Content and Structure  . . .  3
     2.1.  Manifests  . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  CA Repository Publication Point  . . . . . . . . . . . . .  5
     2.3.  EE Repository Publication Point  . . . . . . . . . . . . .  7
   3.  Resource Certificate Publication Repository Considerations . .  7
   4.  Certificate Reissuance and Repositories  . . . . . . . . . . .  8
   5.  Synchronising Repositories . . . . . . . . . . . . . . . . . .  9
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
   Intellectual Property and Copyright Statements . . . . . . . . . . 12
































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1.  Introduction

   To validate attestations made in the context of the Resource Public
   Key Infrastructure (RPKI) relying parties need access to all the
   X.509 / PKIX Resource Certificates, Certificate Revocation Lists
   (CRLs), and signed objects that collectively define the RPKI.

   Each issuer of a certificate, CRL or a signed object makes it
   available for download to replying parties through the publication of
   the object in a RPKI repository.

   The repository system is the central clearing-house for all signed
   objects that must be globally accessible to relying parties.  When
   certificates, CRLs and signed objects are created, they are uploaded
   to a repository publication point, from whence they can be downloaded
   for use by relying parties.

   This document defines a profile for the structure of RPKI
   repositories.  This profile contains the proposed object naming
   scheme, the contents of repository publication points, the contents
   of publication point manifests and a possible internal structure of a
   Repository Cache that is intended to facilitate synchronization
   across a distributed collection of repositories and facilitate
   certificate path construction.

   A Resource Certificate describes an action by an Issuer that binds a
   list of IP address blocks and AS numbers to the Subject of a
   certificate, identified by the unique association of the Subject's
   private key with the public key contained in the Resource
   Certificate.

1.1.  Terminology

   It is assumed that the reader is familiar with the terms and concepts
   described in "Internet X.509 Public Key Infrastructure Certificate
   and Certificate Revocation List (CRL) Profile" [RFC5280], "X.509
   Extensions for IP Addresses and AS Identifiers" [RFC3779], and
   related regional Internet registry address management policy
   documents.


2.  RPKI Repository Publication Point Content and Structure

   RPKI does not use a single repository publication point to publish
   RPKI objects.  Instead, the RPKI repository system is comprised of
   multiple repository publication points.  Each repository publication
   point is uniquely associated with a single RPKI certificate's
   publication point, as defined in the certificate's SUbject



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   Information Authority (SIA) extension.

   This section describes the collection of objects (RPKI certificates,
   CRLs, manifests and signed objects) held in repository publication
   points.

   For every certificate in the PKI, there will be a corresponding
   repository publication point file system directory that is the
   authoritative publication point for all objects signed by the private
   key part of the key pair whose public key part is the subject of this
   certificate (or "all objects verifiable via this certificate").  The
   certificate's Subject Information Authority (SIA) extension provides
   a set of URIs, each of which references this repository publication
   point and a supported access mechanism.  Additionally, a
   certificate's Authority Information Authority (AIA) extension
   contains a URI that references the authoritative location for the CA
   certificate under which the given certificate was issued.  That is,
   if the subject of certificate A has issued certificate B, then the
   AIA extension of certificate B points to certificate A, and the SIA
   extension of certificate A points to a directory containing
   certificate B (see Figure 1).

                      +--------+
           +--------->| Cert A |<----+
           |          | CRLDP  |     |
           |          |  AIA   |     |
           |  +--------- SIA   |     |
           |  |       +--------+     |
           |  |                      |
           |  |                      |
           |  |                      |
           |  |  +-------------------|------------------+
           |  |  |                   |                  |
           |  +->|   +--------+      |   +--------+     |
           |     |   | Cert B |      |   | Cert C |     |
           |     |   | CRLDP ----+   |   | CRLDP -+-+   |
           +----------- AIA   |  |   +----- AIA   | |   |
                 |   |  SIA   |  |       |  SIA   | |   |
                 |   +--------+  |       +--------+ |   |
                 |               V                  |   |
                 |           +---------+            |   |
                 |           | A's CRL |<-----------+   |
                 |           +---------+                |
                 | A's Repository Publication Directory |
                 +--------------------------------------+

   Figure 1: In this example, certificates B and C are issued under
   certificate A. Therefore, the AIA extensions of certificates B and C



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   point to A, and the SIA extension of certificate A points to the
   repository publication point containing certificates B and C, as well
   as A'a CRL.

   The general intent is that an instance of a CA's repository
   publication point contains all the signed products of the Certificate
   Authority, and an End Entity's repository publication point contains
   all the objects signed by the EE.

2.1.  Manifests

   All repository publication points MUST contain a manifest
   [I-D.ietf-sidr-rpki-manifests].  The manifest contains a list of the
   names of all objects contained in a repository publication point
   directory, as well as the hash value of each object's contents.

   The collection of manifests across the entire RPKI is complete, in
   that all published objects are described in precisely one manifest.

2.2.  CA Repository Publication Point

   A CA Certificate has two accessMethods specified in its SIA field.
   The id-ad-caRepository accessMethod has an associated accessLocation
   that points to the the repository publication point of the products
   of this CA, as specified in [I-D.ietf-sidr-res-certs].  The id-ad-
   rpkiManifest accessMethod has an associated access location that
   points to the manifest object, as an object URL, that is associated
   with this repository publication point.  This manifest describes all
   the objects that are to be found in that publication point and the
   hash value of each object (excluding the manifest itself)
   [I-D.ietf-sidr-rpki-manifests].

   In the case of a CA's publication repository in the scope of the
   RPKI, the repository contains the current certificates issued by this
   CA, the most recent CRLs that are associated with the CA's non-
   revoked keypairs, the current manifest, and all objects that are
   signed using a "single-use" EE certificate, where the EE certificate
   was issued by this CA.

   Some guidelines for naming objects in a CA's repository publication
   point are as follows:

   CRL:  The scope of a CRL in the RPKI is all objects issued by a CA
      with a given key pair, implying that publication of successive
      instances of a CA's CRL may overwrite previous instances of CRLs
      signed by the same CA private key in the publication repository.
      It is consistent with this objective that the name chosen for the
      CRL in the publication repository be a value derived from the



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      public key part of the CA's key pair that was used to sign the
      CRL.  One such method of generating a CRL publication name is
      described in section 2.1 of [RFC4387], converting the 160-bit hash
      of the CA's public key value into a 27-character string using a
      modified form of Base64 encoding, with an additional modification
      as proposed in section 5, table 2, of [RFC4648].

   Manifest:  When a new instance of a manifest is published by the CA,
      there is no requirement within the RPKI for any relying party to
      have continuing access to older instances of the CA's manifest.
      This implies that the name chosen for the manifest object in the
      publication repository may be a constant value, implying that
      publication of successive instances of the manifest overwrite the
      previous instance of the manifest within the context of each
      publication repository.

   Certificates:  Within the RPKI framework it is possible that a CA may
      issue a series of certificates for the same subject name, the same
      subject public key, and the same resource collection.  Within the
      context of each such series of certificates a relying party has an
      interest only in the most recently published certificate.  The
      publication repository object name scheme for the CA may use a
      unique name for each such series of certificates, thereby ensuring
      that each successive issued certificate in such a series
      effectively overwrites the previous instance of the certificate
      series in the publication repository.  If the CA adopts a local
      policy that each subject uses a unique key pair for each unique
      instance of a certified resource collection then the CA can use a
      certificate object name scheme that is derived from the subject's
      public key, applying the algorithm described above for CRL object
      names to the subject's public key value.
   Signed Objects:  Within the RPKI framework there are two kinds of EE
      certificates that are used in conjunction with digital
      certificates: "single-use" EE certificates that are used to sign a
      single object, and "multi-use" EE Certificates that may be used to
      sign multiple objects.  In the case of "single-use" EE
      certificates, the single signed object is to be published in the
      same repository publication point as the EE certificate that was
      used to sign the object.  The signed object name scheme for such
      objects can be derived from the associated EE certificate's public
      key, applying the algorithm described above.  The signed object is
      listed in the manifest associated with this repository publication
      point.  In the case of "multi-use" EE certificates the repository
      publication point is described in the following section.

   It is left as an implementation choice as to whether a CA is to use a
   single publication repository for all products of the CA across all
   non-retired keypairs, or to use a distinct publication repository for



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   each non-retired keypair.

   It is not consistent with the specification that multiple CAs share a
   single repository publication point.  Also it is not consistent with
   this specification that a CA repository publication point is shared
   with a "multi-use" EE repository publication point.

2.3.  EE Repository Publication Point

   EE repository publication points are used in conjunction with "multi-
   use" EE Certificates.  In this case the EE Certificate has two
   accessMethods specified in its SIA field.  The id-ad-
   signedObjectRepository accessMethod has an associated accessLocation
   that points to the the repository publication point of the objects
   signed by this EE certificate, as specified in
   [I-D.ietf-sidr-res-certs].  The id-ad-rpkiManifest accessMethod has
   an associated access location that points to the manifest object as
   an object URL, that is associated with this repository publication
   point.  This manifest describes all the signed objects that are to be
   found in that publication point that have been signed by this EE
   certificate, and the hash value of each product (excluding the
   manifest itself) [I-D.ietf-sidr-rpki-manifests].

   In the case of a EE's publication repository in the scope of the
   RPKI, the repository contains objects that have been signed by the
   EE's key pair, and a manifest of all such signed objects.

   The objects published in a EE repository publication point do not
   form a logical sequence, and must be named uniquely in the context of
   the publication repository.

   It is consistent with this specification, but not recommended
   practice, that all subordinate EE certificates of a given CA share a
   common publication repository.  In this case the repository
   publication point would contain multiple manifest objects, one for
   each EE certificate that has placed objects into this common
   publication point.  Each manifest is limited in scope to listing the
   objects signed by the EE certificate.  The implication is that all
   objects signed by a single EE certificate, including the EE's
   manifest, share a base name element that is generated from the public
   key of the EE certificate.  The choice of whether to use a common
   single publication repository or a dedicated publication repository
   for each EE certificate is an implementation choice.


3.  Resource Certificate Publication Repository Considerations

   Each issuer may publish their issued certificates and CRL in any



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   location of their choice.  However, there are a number of
   considerations which guide the choice of a suitable repository
   publication structure.

   o  The publication repository should be hosted on a highly available
      service and high capacity publication platform.

   o  The publication repository should be available using RSYNC.
      Support of additional retrieval methods is the choice of the
      repository operator.  The supported access methods should be
      consistent with the access methods as specified in the SIA of the
      associated CA or EE.

   o  Each CA publication directory in the publication repository should
      contain the products of a single issuer's CA instance, including
      those objects signed by single-use EE certificates that have been
      issued by this CA.  Aside from subdirectories, no other objects
      should be placed in a publication repository directory.

      Any such subdirectory should be the repository publication point
      of a CA or EE certificate that is contained in the directory.
      There are no constraints on the name of a subdirectory.  These
      considerations also apply recursively to subdirectories of these
      directories.

   o  Signed Objects are published in the location indicated by the SIA
      field of the EE certificate that has certified the key pair that
      was used to sign the object.  The choice of the repository
      publication point is determined by the nature of the signing EE
      certificate.  In the case of "multi-use" EE certificates the
      signed object is published in an EE repository publication point
      as referenced by the SIA extension of the EE certificate.  In the
      case of "single-use" EE certificates the signed object is
      published in the repository publication point of the CA
      certifificate that issued the EE certificate, and the SIA
      extension of the single use EE certificate references this object
      rather than the publication directory[I-D.ietf-sidr-res-certs].


4.  Certificate Reissuance and Repositories

   If a CA certificate is reissued, it should not be necessary to
   reissue all certificates signed by the certificate being reissued.
   Therefore, a certification authority SHOULD use a persistent naming
   scheme for the certificates's repository publication point that is
   persistent across certificate reissuance events.  That is, reissued
   certificates should use the same repository publication point as
   previously issued certificates having the same subject and subject



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   public key, and should overwrite previously issued certificates
   within the repository publication point directory.


5.  Synchronising Repositories

   It is possible to perform the validation-related task of certificate
   path construction using retrieval of individual certificates and
   certificate revocation lists using online retrieval of individual
   certificates, sets of candidate certificates and certificate
   revocation lists based on the Authority Information Access, Subject
   Information Access and CRL Distribution Points certificate fields.
   This is not recommended in circumstances where speed and efficiency
   are relevant considerations.  Where an efficient validation function
   is required, it is suggested that the relying party maintain a local
   repository containing a synchronized copy of all valid certificates,
   current certificate revocation lists, and all related signed objects
   that are stored in the local instances of components of the overall
   logical complete certificate repository.

   The general approach to repository synchronization is one of a "top-
   down" walk of the distributed repository structure, commencing with
   the initial configured trust anchor certificates, and then populating
   the the local repository cache will all valid certificates that have
   been issued by these issuers, and then recursively applying the same
   approach to each of these subordinate certificates.  Such a
   repository travescal process would need to support some maximal chain
   length from the initial trust anchors to the current working
   validation point in order to ensure that the process does not follow
   a loop or a non-terminating certificate chain.


6.  Security Considerations

   Repositories are not "protected" structures, and repository retrieval
   operations are vulnerable to various forms of "man-in-the-middle"
   attacks.  Corruption of retrieved objects is detectable by a relying
   party through the RPKI validation of the retrieved object.  Insertion
   of older objects is detectable in part by the CRL.  However, certain
   forms of substitution and removal attacks are not directly
   detectable.  For this reason all published RPKI objects are described
   in a manifest [I-D.ietf-sidr-rpki-manifests].  The manifest can
   improve the level of assurance that a relying party is receiving an
   authentic copy of the repository, and that the set of retrieved
   objects is complete.






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7.  IANA Considerations

   [There are no IANA considerations in this document.]


8.  Normative References

   [I-D.ietf-sidr-res-certs]
              Huston, G., Loomans, R., and G. Michaelson, "A Profile for
              X.509 PKIX Resource Certificates",
              draft-ietf-sidr-res-certs (work in progress), August 2008.

   [I-D.ietf-sidr-rpki-manifests]
              Austein, R., Huston, G., Kent, S., and M. Lepinski,
              "Manifests for the Resource Public Key Infrastructure",
              draft-ietf-sidr-rpki-manifests (work in progress),
              August 2008.

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

   [RFC4387]  Gutmann, P., "Internet X.509 Public Key Infrastructure
              Operational Protocols: Certificate Store Access via HTTP",
              RFC 4387, February 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [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.


Authors' Addresses

   Geoff Huston
   Asia Pacific Network Information Centre

   Email: gih@apnic.net
   URI:   http://www.apnic.net










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   Robert Loomans
   Asia Pacific Network Information Centre

   Email: robertl@apnic.net
   URI:   http://www.apnic.net


   George Michaelson
   Asia Pacific Network Information Centre

   Email: ggm@apnic.net
   URI:   http://www.apnic.net







































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Full Copyright Statement

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Acknowledgment

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   Administrative Support Activity (IASA).





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