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RFC 8209

Proposed STD
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A Profile for BGPsec Router Certificates, Certificate Revocation Lists, and Certification Requests

Updates:    6487


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Internet Engineering Task Force (IETF)                       M. Reynolds
Request for Comments: 8209                                          IPSw
Updates: 6487                                                  S. Turner
Category: Standards Track                                          sn3rd
ISSN: 2070-1721                                                  S. Kent
                                                                     BBN
                                                          September 2017


               A Profile for BGPsec Router Certificates,
        Certificate Revocation Lists, and Certification Requests

Abstract

   This document defines a standard profile for X.509 certificates used
   to enable validation of Autonomous System (AS) paths in the Border
   Gateway Protocol (BGP), as part of an extension to that protocol
   known as BGPsec.  BGP is the standard for inter-domain routing in the
   Internet; it is the "glue" that holds the Internet together.  BGPsec
   is being developed as one component of a solution that addresses the
   requirement to provide security for BGP.  The goal of BGPsec is to
   provide full AS path validation based on the use of strong
   cryptographic primitives.  The end entity (EE) certificates specified
   by this profile are issued to routers within an AS.  Each of these
   certificates is issued under a Resource Public Key Infrastructure
   (RPKI) Certification Authority (CA) certificate.  These CA
   certificates and EE certificates both contain the AS Resource
   extension.  An EE certificate of this type asserts that the router or
   routers holding the corresponding private key are authorized to emit
   secure route advertisements on behalf of the AS(es) specified in the
   certificate.  This document also profiles the format of certification
   requests and specifies Relying Party (RP) certificate path validation
   procedures for these EE certificates.  This document extends the
   RPKI; therefore, this document updates the RPKI Resource Certificates
   Profile (RFC 6487).

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Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8209.

Copyright Notice

   Copyright (c) 2017 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
   (https://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
   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.

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Table of Contents

   1. Introduction ....................................................3
      1.1. Terminology ................................................4
   2. Describing Resources in Certificates ............................4
   3. Updates to RFC 6487 .............................................6
      3.1. BGPsec Router Certificate Fields ...........................6
           3.1.1. Subject .............................................6
           3.1.2. Subject Public Key Info .............................6
           3.1.3. BGPsec Router Certificate Version 3
                  Extension Fields ....................................6
                  3.1.3.1. Basic Constraints ..........................6
                  3.1.3.2. Extended Key Usage .........................6
                  3.1.3.3. Subject Information Access .................7
                  3.1.3.4. IP Resources ...............................7
                  3.1.3.5. AS Resources ...............................7
      3.2. BGPsec Router Certificate Request Profile ..................7
      3.3. BGPsec Router Certificate Validation .......................8
      3.4. Router Certificates and Signing Functions in the RPKI ......8
   4. Design Notes ....................................................9
   5. Implementation Considerations ...................................9
   6. Security Considerations ........................................10
   7. IANA Considerations ............................................10
   8. References .....................................................11
      8.1. Normative References ......................................11
      8.2. Informative References ....................................12
   Appendix A. ASN.1 Module ..........................................14
   Acknowledgements ..................................................15
   Authors' Addresses ................................................15

1.  Introduction

   This document defines a profile for X.509 end entity (EE)
   certificates [RFC5280] for use in the context of certification of
   Autonomous System (AS) paths in the BGPsec protocol.  Such
   certificates are termed "BGPsec Router Certificates".  The holder of
   the private key associated with a BGPsec Router Certificate is
   authorized to send secure route advertisements (BGPsec UPDATEs) on
   behalf of the AS(es) named in the certificate.  A router holding the
   private key is authorized to send route advertisements (to its peers)
   identifying the router's AS number (ASN) as the source of the
   advertisements.  A key property provided by BGPsec is that every AS
   along the AS path can verify that the other ASes along the path have
   authorized the advertisement of the given route (to the next AS along
   the AS path).

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   This document is a profile of [RFC6487], which is a profile of
   [RFC5280]; thus, this document updates [RFC6487].  It establishes
   requirements imposed on a Resource Certificate that is used as a
   BGPsec Router Certificate, i.e., it defines constraints for
   certificate fields and extensions for the certificate to be valid in
   this context.  This document also profiles the certification requests
   used to acquire BGPsec Router Certificates.  Finally, this document
   specifies the Relying Party (RP) certificate path validation
   procedures for these certificates.

1.1.  Terminology

   It is assumed that the reader is familiar with the terms and concepts
   described in "A Profile for X.509 PKIX Resource Certificates"
   [RFC6487], "BGPsec Protocol Specification" [RFC8205], "A Border
   Gateway Protocol 4 (BGP-4)" [RFC4271], "BGP Security Vulnerabilities
   Analysis" [RFC4272], "Considerations in Validating the Path in BGP"
   [RFC5123], and "Capabilities Advertisement with BGP-4" [RFC5492].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Describing Resources in Certificates

   Figure 1 depicts some of the entities in the Resource Public Key
   Infrastructure (RPKI) and some of the products generated by RPKI
   entities.  IANA issues a Certification Authority (CA) certificate to
   each Regional Internet Registry (RIR).  The RIR in turn issues a
   CA certificate to an Internet Service Provider (ISP).  The ISP
   in turn issues EE certificates to itself to enable verification of
   signatures on RPKI signed objects.  The CA also generates Certificate
   Revocation Lists (CRLs).  These CA and EE certificates are referred
   to as "Resource Certificates" and are profiled in [RFC6487].
   [RFC6480] envisioned using Resource Certificates to enable
   verification of manifests [RFC6486] and Route Origin Authorizations
   (ROAs) [RFC6482].  ROAs and manifests include the Resource
   Certificates used to verify them.

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                +---------+   +------+
                | CA Cert |---| IANA |
                +---------+   +------+
                         \
                      +---------+   +-----+
                      | CA Cert |---| RIR |
                      +---------+   +-----+
                              \
                             +---------+   +-----+
                             | CA Cert |---| ISP |
                             +---------+   +-----+
                              / |            | |
                   +-----+   /  |            | |   +-----+
                   | CRL |--+   |            | +---| ROA |
                   +-----+      |            |     +-----+
                                |            |   +----------+
                       +----+   |            +---| Manifest |
                     +-| EE |---+                +----------+
                     | +----+
                     +-----+

                                 Figure 1

   This document defines another type of Resource Certificate, which is
   referred to as a "BGPsec Router Certificate".  The purpose of this
   certificate is explained in Section 1 and falls within the scope of
   appropriate uses defined within [RFC6484].  The issuance of BGPsec
   Router Certificates has minimal impact on RPKI CAs because the RPKI
   CA certificate and CRL profile remain unchanged (i.e., they are as
   specified in [RFC6487]).  Further, the algorithms used to generate
   RPKI CA certificates that issue the BGPsec Router Certificates and
   the CRLs necessary to check the validity of the BGPsec Router
   Certificates remain unchanged (i.e., they are as specified in
   [RFC7935]).  The only impact is that RPKI CAs will need to be able to
   process a profiled certificate request (see Section 3.2) signed with
   algorithms found in [RFC8208].  BGPsec Router Certificates are used
   only to verify the signature on the BGPsec certificate request (only
   CAs process these) and the signature on a BGPsec UPDATE message
   [RFC8205] (only BGPsec routers process these); BGPsec Router
   Certificates are not used to process manifests and ROAs or verify
   signatures on Certificates or CRLs.

   This document enumerates only the differences between this profile
   and the profile in [RFC6487].  Note that BGPsec Router Certificates
   are EE certificates, and as such there is no impact on the algorithm
   agility procedure described in [RFC6916].

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3.  Updates to RFC 6487

3.1.  BGPsec Router Certificate Fields

   A BGPsec Router Certificate is consistent with the profile in
   [RFC6487] as modified by the specifications in this section.  As
   such, it is a valid X.509 public key certificate and consistent with
   the PKIX profile [RFC5280].  The differences between this profile and
   the profile in [RFC6487] are specified in this section.

3.1.1.  Subject

   Encoding options for the common name that are supported are
   printableString and UTF8String.  For BGPsec Router Certificates, it
   is RECOMMENDED that the common name attribute contain the literal
   string "ROUTER-" followed by the 32-bit ASN [RFC3779] encoded as
   eight hexadecimal digits and that the serial number attribute contain
   the 32-bit BGP Identifier [RFC4271] (i.e., the router ID) encoded as
   eight hexadecimal digits.  If there is more than one ASN, the choice
   of which to include in the common name is at the discretion of the
   Issuer.  If the same certificate is issued to more than one router
   (and hence the private key is shared among these routers), the choice
   of the router ID used in this name is at the discretion of the
   Issuer.

3.1.2.  Subject Public Key Info

   Refer to Section 3.1 of [RFC8208].

3.1.3.  BGPsec Router Certificate Version 3 Extension Fields

3.1.3.1.  Basic Constraints

   BGPsec speakers are EEs; therefore, the Basic Constraints extension
   must not be present, as per [RFC6487].

3.1.3.2.  Extended Key Usage

   BGPsec Router Certificates MUST include the Extended Key Usage (EKU)
   extension.  As specified in [RFC6487], this extension must not be
   marked critical.  This document defines one EKU for BGPsec Router
   Certificates:

     id-kp OBJECT IDENTIFIER ::=
        { iso(1) identified-organization(3) dod(6) internet(1)
          security(5) mechanisms(5) pkix(7) kp(3) }

     id-kp-bgpsec-router OBJECT IDENTIFIER ::= { id-kp 30 }

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   A BGPsec router MUST require the EKU extension be present in a BGPsec
   Router Certificate it receives.  If multiple KeyPurposeId values are
   included, the BGPsec routers need not recognize all of them, as long
   as the required KeyPurposeId value is present.  BGPsec routers MUST
   reject certificates that do not contain the BGPsec Router EKU even if
   they include the anyExtendedKeyUsage OID defined in [RFC5280].

3.1.3.3.  Subject Information Access

   This extension is not used in BGPsec Router Certificates.  It MUST be
   omitted.

3.1.3.4.  IP Resources

   This extension is not used in BGPsec Router Certificates.  It MUST be
   omitted.

3.1.3.5.  AS Resources

   Each BGPsec Router Certificate MUST include the AS Resources
   extension, as specified in Section 4.8.11 of [RFC6487].  The
   AS Resources extension MUST include one or more ASNs, and the
   "inherit" element MUST NOT be specified.

3.2.  BGPsec Router Certificate Request Profile

   Refer to Section 6 of [RFC6487].  The only differences between this
   profile and the profile in [RFC6487] are as follows:

   o  The Basic Constraints extension:

      If included, the CA MUST NOT honor the cA boolean if set to TRUE.

   o  The EKU extension:

      If included, id-kp-bgpsec-router MUST be present (see
      Section 3.1.3.2).  If included, the CA MUST honor the request for
      id-kp-bgpsec-router.

   o  The Subject Information Access (SIA) extension:

      If included, the CA MUST NOT honor the request to include the
      extension.

   o  The SubjectPublicKeyInfo field is specified in [RFC8208].

   o  The request is signed with the algorithms specified in [RFC8208].

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3.3.  BGPsec Router Certificate Validation

   The validation procedure used for BGPsec Router Certificates is
   identical to the validation procedure described in Section 7 of
   [RFC6487] (and any RFC that updates that procedure), as modified
   below.  For example, in step 3 (of the criteria listed in Section 7.2
   of [RFC6487]), "The certificate contains all fields that MUST be
   present" refers to the fields that are required by this
   specification.

   The differences are as follows:

   o  BGPsec Router Certificates MUST include the BGPsec Router EKU
      defined in Section 3.1.3.2.

   o  BGPsec Router Certificates MUST NOT include the SIA extension.

   o  BGPsec Router Certificates MUST NOT include the IP Resources
      extension.

   o  BGPsec Router Certificates MUST include the AS Resources
      extension.

   o  BGPsec Router Certificates MUST include the subjectPublicKeyInfo
      field described in [RFC8208].

   NOTE: BGPsec RPs will need to support the algorithms in [RFC8208],
   which are used to validate BGPsec signatures, as well as the
   algorithms in [RFC7935], which are needed to validate signatures on
   BGPsec certificates, RPKI CA certificates, and RPKI CRLs.

3.4.  Router Certificates and Signing Functions in the RPKI

   As described in Section 1, the primary function of BGPsec Router
   Certificates in the RPKI is for use in the context of certification
   of AS paths in the BGPsec protocol.

   The private key associated with a router EE certificate may be used
   multiple times in generating signatures in multiple instances of the
   BGPsec_PATH attribute Signature Segments [RFC8205].  That is, the
   BGPsec Router Certificate is used to validate multiple signatures.

   BGPsec Router Certificates are stored in the issuing CA's repository,
   where a repository following [RFC6481] MUST use a .cer filename
   extension for the certificate file.

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4.  Design Notes

   The BGPsec Router Certificate profile is based on the Resource
   Certificate profile as specified in [RFC6487].  As a result, many of
   the design choices herein are a reflection of the design choices that
   were taken in that prior work.  The reader is referred to [RFC6484]
   for a fuller discussion of those choices.

   CAs are required by the Certificate Policy (CP) [RFC6484] to issue
   properly formed BGPsec Router Certificates regardless of what is
   present in the certificate request, so there is some flexibility
   permitted in the certificate requests:

   o  BGPsec Router Certificates are always EE certificates; therefore,
      requests to issue a CA certificate result in EE certificates;

   o  BGPsec Router Certificates are always EE certificates; therefore,
      requests for Key Usage extension values keyCertSign and cRLSign
      result in certificates with neither of these values;

   o  BGPsec Router Certificates always include the BGPsec Router EKU
      value; therefore, requests without the value result in
      certificates with the value; and,

   o  BGPsec Router Certificates never include the SIA extension;
      therefore, requests with this extension result in certificates
      without the extension.

   Note that this behavior is similar to the CA including the
   AS Resources extension in issued BGPsec Router Certificates, despite
   the fact that it is not present in the request.

5.  Implementation Considerations

   This document permits the operator to include a list of ASNs in a
   BGPsec Router Certificate.  In that case, the router certificate
   would become invalid if any one of the ASNs is removed from any
   superior CA certificate along the path to a trust anchor.  Operators
   could choose to avoid this possibility by issuing a separate BGPsec
   Router Certificate for each distinct ASN, so that the router
   certificates for ASNs that are retained in the superior CA
   certificate would remain valid.

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6.  Security Considerations

   The security considerations of [RFC6487] apply.

   A BGPsec Router Certificate will fail RPKI validation as defined in
   [RFC6487] because the cryptographic algorithms used are different.
   Consequently, an RP needs to identify the EKU to determine the
   appropriate Validation constraint.

   A BGPsec Router Certificate is an extension of the RPKI [RFC6480] to
   encompass routers.  It is a building block of BGPsec and is used to
   validate signatures on BGPsec Signature Segment origination of
   signed path segments [RFC8205].  Thus, its essential security
   function is the secure binding of one or more ASNs to a public key,
   consistent with the RPKI allocation/assignment hierarchy.

   Hash functions [RFC8208] are used when generating the two key
   identifier extensions (i.e., Subject Key Identifier and Issuer Key
   Identifier) included in BGPsec certificates.  However, as noted in
   [RFC6818], collision resistance is not a required property of one-way
   hash functions when used to generate key identifiers.  Regardless,
   hash collisions are unlikely, but they are possible, and if detected
   an operator should be alerted.  A Subject Key Identifier collision
   might cause the incorrect certificate to be selected from the cache,
   resulting in a failed signature validation.

7.  IANA Considerations

   This document makes use of two OIDs in the SMI registry for PKIX.
   One is for the ASN.1 module [X680] [X690] in Appendix A, and it comes
   from the "SMI Security for PKIX Module Identifier" IANA registry
   (id-mod-bgpsec-eku).  The other is for the BGPsec Router EKU defined
   in Section 3.1.3.2 and Appendix A, and it comes from the "SMI
   Security for PKIX Extended Key Purpose" IANA registry
   (id-kp-bgpsec-router).  These OIDs were assigned before management of
   the PKIX Arc was handed to IANA.  The references in those registries
   have been updated to point to this document.

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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,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3779]  Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for
              IP Addresses and AS Identifiers", RFC 3779,
              DOI 10.17487/RFC3779, June 2004,
              <https://www.rfc-editor.org/info/rfc3779>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc6481>.

   [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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc6487>.

   [RFC7935]  Huston, G. and G. Michaelson, Ed., "The Profile for
              Algorithms and Key Sizes for Use in the Resource Public
              Key Infrastructure", RFC 7935, DOI 10.17487/RFC7935,
              August 2016, <https://www.rfc-editor.org/info/rfc7935>.

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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in
              RFC 2119 Key Words", BCP 14, RFC 8174,
              DOI 10.17487/RFC8174, May 2017,
              <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8205]  Lepinski, M., Ed., and K. Sriram, Ed., "BGPsec Protocol
              Specification", RFC 8205, DOI 10.17487/RFC8205,
              September 2017,
              <https://www.rfc-editor.org/info/rfc8205>.

   [RFC8208]  Turner, S. and O. Borchert, "BGP Algorithms, Key Formats,
              and Signature Formats", RFC 8208, DOI 10.17487/RFC8208,
              September 2017,
              <https://www.rfc-editor.org/info/rfc8208>.

   [X680]     ITU-T, "Information technology - Abstract Syntax
              Notation One (ASN.1): Specification of basic notation",
              ITU-T Recommendation X.680, ISO/IEC 8824-1, August 2015,
              <https://www.itu.int/rec/T-REC-X.680/en>.

   [X690]     ITU-T, "Information technology - ASN.1 encoding rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1,
              August 2015, <https://www.itu.int/rec/T-REC-X.690/en>.

8.2.  Informative References

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,
              <https://www.rfc-editor.org/info/rfc4272>.

   [RFC5123]  White, R. and B. Akyol, "Considerations in Validating the
              Path in BGP", RFC 5123, DOI 10.17487/RFC5123,
              February 2008, <https://www.rfc-editor.org/info/rfc5123>.

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492,
              February 2009, <https://www.rfc-editor.org/info/rfc5492>.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <https://www.rfc-editor.org/info/rfc6480>.

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

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   [RFC6484]  Kent, S., Kong, D., Seo, K., and R. Watro, "Certificate
              Policy (CP) for the Resource Public Key Infrastructure
              (RPKI)", BCP 173, RFC 6484, DOI 10.17487/RFC6484,
              February 2012, <https://www.rfc-editor.org/info/rfc6484>.

   [RFC6818]  Yee, P., "Updates to the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 6818, DOI 10.17487/RFC6818,
              January 2013, <https://www.rfc-editor.org/info/rfc6818>.

   [RFC6916]  Gagliano, R., Kent, S., and S. Turner, "Algorithm Agility
              Procedure for the Resource Public Key Infrastructure
              (RPKI)", BCP 182, RFC 6916, DOI 10.17487/RFC6916,
              April 2013, <https://www.rfc-editor.org/info/rfc6916>.

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Appendix A.  ASN.1 Module

   BGPSECEKU { iso(1) identified-organization(3) dod(6) internet(1)
     security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-bgpsec-eku(84) }

     DEFINITIONS EXPLICIT TAGS ::=

     BEGIN

     -- EXPORTS ALL --

     -- IMPORTS NOTHING --

     -- OID Arc --

     id-kp  OBJECT IDENTIFIER  ::= {
       iso(1) identified-organization(3) dod(6) internet(1)
       security(5) mechanisms(5) pkix(7) kp(3) }

     -- BGPsec Router Extended Key Usage --

     id-kp-bgpsec-router OBJECT IDENTIFIER ::= { id-kp 30 }

     END

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Acknowledgements

   We would like to thank Geoff Huston, George Michaelson, and Robert
   Loomans for their work on [RFC6487], which this work is based on.  In
   addition, the efforts of Matt Lepinski were instrumental in preparing
   this work.  Additionally, we'd like to thank Rob Austein, Roque
   Gagliano, Richard Hansen, Geoff Huston, David Mandelberg, Sandra
   Murphy, and Sam Weiler for their reviews and comments.

Authors' Addresses

   Mark Reynolds
   Island Peak Software
   328 Virginia Road
   Concord, MA  01742
   United States of America

   Email: mcr@islandpeaksoftware.com


   Sean Turner
   sn3rd

   Email: sean@sn3rd.com


   Stephen Kent
   Raytheon BBN Technologies
   10 Moulton St.
   Cambridge, MA  02138
   United States of America

   Email: kent@alum.mit.edu