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External Keys For Use In Internet X.509 Certificates
draft-ounsworth-lamps-pq-external-pubkeys-05

Document Type Active Internet-Draft (individual)
Authors Mike Ounsworth , John Gray , D. Hook , Markku-Juhani O. Saarinen
Last updated 2024-10-08
Replaces draft-ounsworth-pq-external-pubkeys
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draft-ounsworth-lamps-pq-external-pubkeys-05
LAMPS                                                       M. Ounsworth
Internet-Draft                                                   J. Gray
Updates: {"RFC5280"=>nil} (if approved)                          Entrust
Intended status: Standards Track                                 D. Hook
Expires: 11 April 2025                                         KeyFactor
                                                       M.-J. O. Saarinen
                                                      Tampere University
                                                          8 October 2024

          External Keys For Use In Internet X.509 Certificates
              draft-ounsworth-lamps-pq-external-pubkeys-05

Abstract

   Many of the post quantum cryptographic algorithms have large public
   keys.  In the interest of reducing bandwidth of transitting X.509
   certificates, this document defines new public key and algorithms for
   referencing external public key data by hash, and location, for
   example URL.  This mechanism is designed to mimic the behaviour of an
   Authority Information Access extension.

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at
   https://EntrustCorporation.github.io/draft-pq-external-pubkeys/draft-
   ounsworth-pq-external-pubkeys.html.  Status information for this
   document may be found at https://datatracker.ietf.org/doc/draft-
   ounsworth-lamps-pq-external-pubkeys/.

   Source for this draft and an issue tracker can be found at
   https://github.com/EntrustCorporation/draft-pq-external-pubkeys.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 11 April 2025.

Copyright Notice

   Copyright (c) 2024 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  External Value  . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  External Public Key . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Module Registration - SMI Security for PKIX Module
           Identifier  . . . . . . . . . . . . . . . . . . . . . . .   4
       3.1.1.  Object Identifier Registrations - SMI Security for PKIX
               Algorithms  . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
     4.1.  CSRs and CT logs  . . . . . . . . . . . . . . . . . . . .   4
   5.  Appendices  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  ASN.1 Module  . . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  Samples . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.3.  Intellectual Property Considerations  . . . . . . . . . .   9
   6.  Contributors and Acknowledgements . . . . . . . . . . . . . .   9
     6.1.  Making contributions  . . . . . . . . . . . . . . . . . .   9
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

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2.  External Value

   The id-external-value algorithm identifier is used for identifying a
   public key or signature which is provided as a reference to external
   data.

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

   EDNOTE: for prototyping purposes, id-external-value ::=
   1.3.6.1.4.1.22554.4.2

   The corresponding subjectPublicKey is the DER encoding of the
   following structure:

   ExternalValue ::= SEQUENCE {
     location     GeneralNames,
     hashAlg      AlgorithmIdentifier,
     hashVal      OCTET STRING
   }

   Upon retrieval of the referenced data, the hash of the OCTET STRING
   of the retrieved data (removing base64 encoding as per [RFC4648] if
   necessary) MUST be verified using hashAlg to match the
   ExternalPublicKey.hash value.

   GeneralNames is defined in [RFC5280] as

   GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

   which we use instead of GeneralName so that certificate issuers can
   specify multiple backup key servers for high availability or specify
   key identifiers in multiple formats if the corresponding public keys
   will be distributed in multiple keystore formats.  When multiple key
   locations are specified, they MUST represent alternative locations
   for retrieval of the same key and MUST NOT be used as a mechanism to
   place multiple subject keys into a single certificate.  Thus, when
   multiple key locations are specified, the client MAY try them in any
   order and stop when it successfully retrieves a public key whose hash
   matches hashVal.

2.1.  External Public Key

   When used with a public key, algorithm parameters for id-external-
   value are absent.

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   When ExternalValue is placed into a
   SubjectPublicKeyInfo.subjectPublicKey, the ExternalValue.location
   MUST refer to a DER-encoded SubjectPublicKeyInfo, which MAY be base64
   encoded as per [RFC4648] for easier transport over text protocols.

3.  IANA Considerations

   ## Object Identifier Allocations

3.1.  Module Registration - SMI Security for PKIX Module Identifier

   *  Decimal: IANA Assigned - *Replace TBDMOD*

   *  Description: EXTERNAL-PUBKEY-2023 - id-mod-external-pubkey

   *  References: This Document

3.1.1.  Object Identifier Registrations - SMI Security for PKIX
        Algorithms

   *  Attest Statement

      -  Decimal: IANA Assigned - Replace *TBDOID*

      -  Description: id-external-value

      -  References: This Document

4.  Security Considerations

   There are no security implications to externalizing a public key from
   a certificate as described in this draft.  It is of course possible
   for a malicious actor to replace or tamper with the public key data
   at the referenced location, but since the hash of the public key data
   is included in the signed certificate, any such tampering will be
   detected and the certificate verification will fail.  For this
   reason, external public key data MAY be served over an insecure
   channel such as HTTP.

4.1.  CSRs and CT logs

   In practice, situations will arise where the
   ExternalPublicKey.location refers to a location which is not publicly
   available either because it is in a local keystore, on a private
   network, or no longer being hosted.

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   Not having the public key in a certificate signing request (CSR)
   could make it substantially harder for CAs to perform vetting of the
   key, for example for cryptographic strength or checking for prior
   revocation due to key compromise.  A certificate requester MUST make
   the full public key available to the CA at the time of certificate
   request either by ensuring that the link in the
   ExternalPublicKey.location is visible to the CA, or by supplying the
   full public key to the CA out of band.

   Not having the public key in Certificate Transparency (CT) logs could
   make it substantially harder for researchers to perform auditing
   tasks on CT logs.  This may require additional CT mechanisms.

5.  Appendices

5.1.  ASN.1 Module

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EXTERNAL-PUBKEY-2023
           {iso(1) identified-organization(3) dod(6) internet(1) security(5)
       mechanisms(5) pkix(7) id-mod(0) id-mod-external-pubkey(TBDMOD)}

DEFINITIONS IMPLICIT TAGS ::= BEGIN

EXPORTS ALL;

IMPORTS

  GeneralNames
  FROM PKIX1Implicit-2009
      {iso(1) identified-organization(3) dod(6) internet(1) security(5)
      mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59)}

  AlgorithmIdentifier{}
  FROM AlgorithmInformation-2009
      {iso(1) identified-organization(3) dod(6) internet(1) security(5)
      mechanisms(5) pkix(7) id-mod(0)
      id-mod-algorithmInformation-02(58)}

;

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

ExternalValue ::= SEQUENCE {
  location     GeneralNames,
  hashAlg      AlgorithmIdentifier,
  hashVal      OCTET STRING
}

END

5.2.  Samples

   Here is a sample of a Kyber1024 end entity certificate with an
   external public key.  A trust anchor certificate using the algorithm
   ecdsaWithSHA256 is provided so that the Kyber1024 End Entity
   certificate can be verified.

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   This is a modest example demonstrating a 550 byte Kyber1024
   certificate and a 2.2 kb external Kyber1024 public key.  This
   "compression" effect will be even more pronounced with algorithms
   such as Classic McEliece which have public keys in the hundreds of
   kilobytes; with the external public key mechanism, the size of the
   certificate remains constant regardless of how large the externalized
   subject public key is.

   End entity Kyber1024 Certificate with ExternalValue public key:

   -----BEGIN CERTIFICATE-----
   MIIBbDCCARGgAwIBAgIGAYro4QFGMAoGCCqGSM49BAMCMDoxDjAMBgNVBAMMBVFT
   IENBMRswGQYDVQQKDBJRdWFudGl0eSBTdXJ2ZXlvcnMxCzAJBgNVBAYTAlhYMB4X
   DTIzMTAwMTAxMzYxNFoXDTI0MDEwOTAxMzYxNFowHTEbMBkGA1UEAwwSRXRoZWwg
   dGhlIEFhcmR2YXJrMGkwDAYKKwYBBAGBsBoEAgNZADBWMCWGI2ZpbGU6Ly9sb2Nh
   bF9rZXlzZXJ2ZXIvc3VydmV5b3JzLmRiMAsGCWCGSAFlAwQCAQQg0K1P456WkMCO
   RxsGOm271ynblXxFCgkTDI78by/RRJCjEDAOMAwGA1UdEwEB/wQCMAAwCgYIKoZI
   zj0EAwIDSQAwRgIhANqC6ZVDVrgaFFPxJcnhJO6kRGU9dHv5vRDcf2paXxSfAiEA
   2s/xoctsB1oCisbjK9HCUw/rzXoVKhkt1ZEXuapJYCk=
   -----END CERTIFICATE-----

   For illustrative purposes, the SubjectPublicKeyInfo within the end
   entity certificate decodes as:

 subjectPublicKeyInfo SubjectPublicKeyInfo SEQUENCE (2 elem)
       algorithm AlgorithmIdentifier SEQUENCE (1 elem)
         algorithm OBJECT IDENTIFIER 1.3.6.1.4.1.22554.4.2 ExternalValue
       subjectPublicKey BIT STRING (704 bit)
         SEQUENCE (3 elem)
           SEQUENCE (1 elem)
             [6] (35 byte) file://local_keyserver/surveyors.db
           SEQUENCE (1 elem)
             OBJECT IDENTIFIER 2.16.840.1.101.3.4.2.1 sha-256
           OCTET STRING (32 byte) D0AD4FE39E9690C08E4...

   The external public key object referenced by the end entity
   certificate is:

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   -----BEGIN PUBLIC KEY-----
   MIIGNDANBgsrBgEEAYGwGgUGAwOCBiEAPEFAYjZ9CljJTDJiJcKBIVCH6Clk3DDA
   ybVRPdsXT6An/mAzlVPHjRtginkcrKIlgRq7lhyoyjVmqkqso1wQGON2vZYM8rwU
   UZFyGUcwykY2bLWJypBvopmUDGumCnARrNqcqRS4zHokOFWZXqcxnVx8DvZsoDc4
   LNIEALKh6vFVx1hZ6txEKtxqxrbC1PGsZ4Z1Z9VY3tB/YJkVKmDLqxcrmwFyAHki
   CEtoaqSxkdB9cBPIlegidjQJS6EqO8aztxu4yWax/jbFu6FOC1cJS2KsBNOjAZvE
   cMhQIGK0R2a6/tGk6TZBHZtHdlYX6udW5OEnW3Aj49On6cMT2ZMx/vlpsTu0DSoX
   lvlJjyiWKxalCNQOGcdMLKNaCOk8NmxLsVdck6WtexiRC6WhccaVR0SZoeO4DBBv
   O7C8mbOrXyyngGmiplNr6oJaY5JbLTMaCsJhiNxvdmLAtxy8EcpRV1FmMkOtqdKX
   FvCwOwxfRGtxDPlOmAE6AqiZfpdmGAGax5XBbQkK5TDErHIidLbGf3IcQzSBOyFw
   HPLG+lXGiZRFBFsmioikpjO0K+jKkWJPFNcb0SOYcktgMxGxZeMpQHHDpSeyn7GM
   uCwVr1BFW8x3S3y+AgMLgEZT3HIPyyljDNwBC1U15sES0zgpV1vB5neQMeBU98AP
   VpFYJDVDhBJgS4qmJfh1aFuQn3HPT8BQYkzBnve36sKKDhmIAYACyEsMKWJZyhix
   dkUH4ls4v+o6MrEoLFZZKuNzowNujlq882NeG/a5GCYTN6gp+PVAh5KbHad9Miic
   +GJKlMPOsJUxzZGEw8iAoBQCZ9dSHdhSDiSPxTsoOso1qyx8dWdJh5AfmQAK7AWi
   sZh054M67rtaTcpLVbqK8DJiFLsItNhu0JsuUpNNy+RxhUC6TiecgkYWPCtnWMuT
   /iFghcTLckzO+RrGAedklNEJ7BM8lkq/qLMXqfmu4/aV1OVVpxuyt/YSc1kOPSpS
   cYTC5gGx85NWpEqmmuUIi/OslEcCeLNl0GgyvFSxncR4eVQ0LDxj1TbOk9t5GVE8
   3IDMZxioK5spypm4jKRFqeRKBWKtzCZCm2MciKtEAZUXOSk7qOl8Sig9TeVUg5LP
   YqmZKCoHeBiKjjlnHxQ5aEM7Dfk8HaWl2IghOXdizPi15XFmrhfLqJijyDQq8xts
   ibR0yBNXc7BGkjGzTLgAe4UZZncvYFsKjehM1umfpNu1vztnpEt35lWc6UIYezvJ
   CDBGWdqAJEFJBflwzpgvF2lTIumTTVazePsCAAg38mg1qprFCNcikcmn0PuwUHmS
   Iza1c9UX/HK4QENt9CyLnKl0vmPEtPWOuvge9Belc9KUibHHBCI24Mg6AbYv2dLO
   7ZEBj6krLpUkkEtGTke5zVwRdFMK6+kP4FG9CpVfqNpC7sO0mACkeAMZSiAderS3
   MgaiH1RpkGkM11kG/IM6U3vAPMAgO4xHM4fB3Wgf5reBC8ZRR5liYGSDZ9KOHrkw
   ISZXNaEYLJFBVXd5g/KrsxQ5AWKxqPsMFMW6+Ih3onQ8R5kIkbxM6/U72nmKOAC+
   9bQuCLBqIJo3GFM087B+LmIW5ZJ6FVV9vSIvaDhrBJiHwQSGsssT+2CntGE+aDxh
   MaVAuLlijgSerBcHkOKhQFAXIKehOENcMfxIW0w4CBCVQrxbUpIiAvpjL0nNUoej
   GngA+euFD4ZESMzP1UICokOyZRS6VpSQn9ozfDxMxlBPt/M6zwOGt0W9jhacjrIs
   IyxB3Dm93ysDnaRRmtOWgAAB80ZKNRBp28uWtUbJYzermLmUNQsWK6I5P2y8JogB
   3htoryUSduEXYOeAVTCYnmgf3yJswznFPNhGZpNoJ2NnJuKHS7o0OCVRpbuRXMOh
   TcMNFyc8+8y//Lpu38kDC1fPK6pW9UVhbKRGFAQWpKonWzDGaeihoDQcP1RD8VUv
   Y2w4MoOpNkdsDgEmoGkv+1EiwLSbThpes1wGa/kx7ihwbAYvuOjFGZIU4Dp+rjJ1
   Unk1erFIlayhGOAr5fWaeNOV3QUK9aSPyVV5YRDXZRKJbaJXDla8JLDOCKeO4aV6
   JHIT3nFqKNQ=
   -----END PUBLIC KEY-----

   For illustrative purposes, the key data, which is itself a
   SubjectPublicKeyInfo, decodes as:

   SEQUENCE (2 elem)
     SEQUENCE (1 elem)
       OBJECT IDENTIFIER 1.3.6.1.4.1.22554.5.6.3 Kyber1024
     BIT STRING (12544 bit) 001111000100000101000

   The following trust anchor certificate can be used to validate the
   above end entity certificate.

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   -----BEGIN CERTIFICATE-----
   MIIBfTCCASSgAwIBAgIGAYro4QBFMAoGCCqGSM49BAMCMDoxDjAMBgNVBAMMBVFT
   IENBMRswGQYDVQQKDBJRdWFudGl0eSBTdXJ2ZXlvcnMxCzAJBgNVBAYTAlhYMB4X
   DTIzMTAwMTAxMzYxNFoXDTI0MDEwOTAxMzYxNFowOjEOMAwGA1UEAwwFUVMgQ0Ex
   GzAZBgNVBAoMElF1YW50aXR5IFN1cnZleW9yczELMAkGA1UEBhMCWFgwWTATBgcq
   hkjOPQIBBggqhkjOPQMBBwNCAASZNnsQba2aDhAfhCTE670YBBvGfo7cU69VR2I+
   NQt321Feh+Au0/S+RobWtyx6JnFnAb/Y00YhQdA1liz0i4lFoxYwFDASBgNVHRMB
   Af8ECDAGAQH/AgEAMAoGCCqGSM49BAMCA0cAMEQCIHV0TdjJm9vCn3k93xhTXMQ0
   D8tQuzXJtFXNGtKk8OQQAiBn8yKLzreor7QrdGUHCH7g0kaDcyI4xXn95aPjgi/V
   NA==
   -----END CERTIFICATE-----

5.3.  Intellectual Property Considerations

   None.

6.  Contributors and Acknowledgements

   This document incorporates contributions and comments from a large
   group of experts.  The Editors would especially like to acknowledge
   the expertise and tireless dedication of the following people, who
   attended many long meetings and generated millions of bytes of
   electronic mail and VOIP traffic over the past year in pursuit of
   this document:

   Serge Mister (Entrust).

   We are grateful to all, including any contributors who may have been
   inadvertently omitted from this list.

   This document borrows text from similar documents, including those
   referenced below.  Thanks go to the authors of those documents.
   "Copying always makes things easier and less error prone" -
   [RFC8411].

6.1.  Making contributions

   Additional contributions to this draft are welcome.  Please see the
   working copy of this draft at, as well as open issues at:

   https://github.com/EntrustCorporation/draft-ounsworth-pq-external-
   keys

7.  Normative References

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/rfc/rfc4648>.

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   [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/rfc/rfc5280>.

   [RFC8411]  Schaad, J. and R. Andrews, "IANA Registration for the
              Cryptographic Algorithm Object Identifier Range",
              RFC 8411, DOI 10.17487/RFC8411, August 2018,
              <https://www.rfc-editor.org/rfc/rfc8411>.

Authors' Addresses

   Mike Ounsworth
   Entrust Limited
   1000 Innovation Drive
   Ottawa, Ontario  K2K 1E3
   Canada
   Email: mike.ounsworth@entrust.com

   J. Gray
   Entrust
   Email: john.gray@entrust.com

   D. Hook
   KeyFactor
   Email: david.hook@keyfactor.com

   Markku-Juhani O. Saarinen
   Tampere University
   Finland
   Email: markku-juhani.saarinen@tuni.fi

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