Internet Engineering Task Force (IETF)                       J. Snijders
Request for Comments: 9323                                        Fastly
Category: Standards Track                                    T. Harrison
ISSN: 2070-1721                                                    APNIC
                                                             B. Maddison
                                                              Workonline
                                                           November 2022


              A Profile for RPKI Signed Checklists (RSCs)

Abstract

   This document defines a Cryptographic Message Syntax (CMS) protected
   content type for use with the Resource Public Key Infrastructure
   (RPKI) to carry a general-purpose listing of checksums (a
   'checklist').  The objective is to allow for the creation of an
   attestation, termed an "RPKI Signed Checklist (RSC)", which contains
   one or more checksums of arbitrary digital objects (files) that are
   signed with a specific set of Internet Number Resources.  When
   validated, an RSC confirms that the respective Internet resource
   holder produced the RSC.

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/rfc9323.

Copyright Notice

   Copyright (c) 2022 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
     1.1.  Requirements Language
   2.  RSC Profile and Distribution
     2.1.  RSC EE Certificates
   3.  The RSC eContentType
   4.  The RSC eContent
     4.1.  Version
     4.2.  Resources
       4.2.1.  ConstrainedASIdentifiers Type
       4.2.2.  ConstrainedIPAddrBlocks Type
     4.3.  digestAlgorithm
     4.4.  checkList
       4.4.1.  FileNameAndHash
   5.  RSC Validation
   6.  Verifying Files or Data Using RSC
   7.  Operational Considerations
   8.  Security Considerations
   9.  IANA Considerations
     9.1.  SMI Security for S/MIME CMS Content Type
           (1.2.840.113549.1.9.16.1)
     9.2.  RPKI Signed Objects
     9.3.  RPKI Repository Name Schemes
     9.4.  SMI Security for S/MIME Module Identifier
           (1.2.840.113549.1.9.16.0)
     9.5.  Media Types
   10. References
     10.1.  Normative References
     10.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   This document defines a Cryptographic Message Syntax (CMS) [RFC5652]
   [RFC6268] protected content type for a general-purpose listing of
   checksums (a 'checklist'), for use with the Resource Public Key
   Infrastructure (RPKI) [RFC6480].  The CMS protected content type is
   intended to provide for the creation and validation of an RPKI Signed
   Checklist (RSC), a checksum listing signed with a specific set of
   Internet Number Resources.  The objective is to allow for the
   creation of an attestation that, when validated, provides a means to
   confirm a given Internet resource holder produced the RSC.

   RPKI Signed Checklists are expected to facilitate inter-domain
   business use cases that depend on an ability to verify resource
   holdership.  RPKI-based validation processes are expected to become
   the industry norm for automated Bring Your Own IP (BYOIP) on-boarding
   or establishment of physical interconnections between Autonomous
   Systems (ASes).

   The RSC concept borrows heavily from Resource Tagged Attestation
   (RTA) [RPKI-RTA], Manifests [RFC9286], and OpenBSD's signify utility
   [signify].  The main difference between an RSC and RTA is that the
   RTA profile allows multiple signers to attest a single digital object
   through a checksum of its content, while the RSC profile allows a
   single signer to attest the content of multiple digital objects.  A
   single signer profile is considered a simplification for both
   implementers and operators.

1.1.  Requirements Language

   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.  RSC Profile and Distribution

   RSC follows the Signed Object Template for the RPKI [RFC6488] with
   one exception: because RSCs MUST NOT be distributed through the
   global RPKI repository system, the Subject Information Access (SIA)
   extension MUST be omitted from the RSC's X.509 End-Entity (EE)
   certificate.

   What constitutes suitable transport for RSC files is deliberately
   unspecified.  For example, it might be a USB stick, a web interface
   secured with HTTPS, an email signed with Pretty Good Privacy (PGP), a
   T-shirt printed with a QR code, or a carrier pigeon.

2.1.  RSC EE Certificates

   The Certification Authority (CA) MUST only sign one RSC with each EE
   certificate and MUST generate a new key pair for each new RSC.  This
   type of EE certificate is termed a "one-time-use" EE certificate (see
   Section 3 of [RFC6487]).

3.  The RSC eContentType

   The eContentType for an RSC is defined as id-ct-signedChecklist, with
   Object Identifier (OID) 1.2.840.113549.1.9.16.1.48.

   This OID MUST appear within both the eContentType in the
   encapContentInfo object and the ContentType signed attribute in the
   signerInfo object (see [RFC6488]).

4.  The RSC eContent

   The content of an RSC indicates that a checklist for arbitrary
   digital objects has been signed with a specific set of Internet
   Number Resources.  An RSC is formally defined as follows:

   RpkiSignedChecklist-2022
     { iso(1) member-body(2) us(840) rsadsi(113549)
       pkcs(1) pkcs9(9) smime(16) mod(0)
       id-mod-rpkiSignedChecklist-2022(73) }

   DEFINITIONS EXPLICIT TAGS ::=
   BEGIN

   IMPORTS
     CONTENT-TYPE, Digest, DigestAlgorithmIdentifier
     FROM CryptographicMessageSyntax-2010 -- in [RFC6268]
       { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
         pkcs-9(9) smime(16) modules(0) id-mod-cms-2009(58) }

     IPAddressOrRange, ASIdOrRange
     FROM IPAddrAndASCertExtn -- in [RFC3779]
       { iso(1) identified-organization(3) dod(6) internet(1)
         security(5) mechanisms(5) pkix(7) mod(0)
         id-mod-ip-addr-and-as-ident(30) } ;

   ct-rpkiSignedChecklist CONTENT-TYPE ::=
     { TYPE RpkiSignedChecklist
       IDENTIFIED BY id-ct-signedChecklist }

   id-ct-signedChecklist OBJECT IDENTIFIER ::=
     { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
       pkcs-9(9) id-smime(16) id-ct(1) 48 }

   RpkiSignedChecklist ::= SEQUENCE {
     version [0]           INTEGER DEFAULT 0,
     resources             ResourceBlock,
     digestAlgorithm       DigestAlgorithmIdentifier,
     checkList             SEQUENCE (SIZE(1..MAX)) OF FileNameAndHash }

   FileNameAndHash ::= SEQUENCE {
     fileName              PortableFilename OPTIONAL,
     hash                  Digest }

   PortableFilename ::=
     IA5String (FROM("a".."z" | "A".."Z" | "0".."9" | "." | "_" | "-"))

   ResourceBlock ::= SEQUENCE {
     asID         [0]      ConstrainedASIdentifiers OPTIONAL,
     ipAddrBlocks [1]      ConstrainedIPAddrBlocks OPTIONAL }
     -- at least one of asID or ipAddrBlocks MUST be present
     ( WITH COMPONENTS { ..., asID PRESENT} |
       WITH COMPONENTS { ..., ipAddrBlocks PRESENT } )

   ConstrainedIPAddrBlocks ::=
     SEQUENCE (SIZE(1..MAX)) OF ConstrainedIPAddressFamily

   ConstrainedIPAddressFamily ::= SEQUENCE {
     addressFamily         OCTET STRING (SIZE(2)),
     addressesOrRanges     SEQUENCE (SIZE(1..MAX)) OF IPAddressOrRange }

   ConstrainedASIdentifiers ::= SEQUENCE {
     asnum [0]             SEQUENCE (SIZE(1..MAX)) OF ASIdOrRange }

   END

4.1.  Version

   The version number of the RpkiSignedChecklist MUST be 0.

4.2.  Resources

   The resources contained here are the resources used to mark the
   attestation and MUST be a subset of the set of resources listed by
   the EE certificate carried in the CMS certificates field.

   If the asID field is present, it MUST contain an instance of
   ConstrainedASIdentifiers.

   If the ipAddrBlocks field is present, it MUST contain an instance of
   ConstrainedIPAddrBlocks.

   At least one of asID or ipAddrBlocks MUST be present.

   ConstrainedASIdentifiers and ConstrainedIPAddrBlocks are specified
   such that the resulting DER-encoded data instances are binary
   compatible with ASIdentifiers and IPAddrBlocks (defined in
   [RFC3779]), respectively.

   Implementations encountering decoding errors whilst attempting to
   read DER-encoded data using this specification should be aware of the
   possibility that the data may have been encoded using an
   implementation intended for use with [RFC3779].  Such data may
   contain elements prohibited by the current specification.

   Attempting to decode the errored data using the more permissive
   specification contained in [RFC3779] may enable implementors to
   gather additional context for use when reporting errors to the user.

   However, implementations MUST NOT ignore errors resulting from the
   more restrictive definitions contained herein; in particular, such
   errors MUST cause the validation procedure described in Section 5 to
   fail.

4.2.1.  ConstrainedASIdentifiers Type

   ConstrainedASIdentifiers is a SEQUENCE consisting of a single field,
   asnum, which in turn contains a SEQUENCE OF one or more ASIdOrRange
   instances as defined in [RFC3779].

   ConstrainedASIdentifiers is defined such that the resulting DER-
   encoded data are binary compatible with ASIdentifiers defined in
   [RFC3779].

4.2.2.  ConstrainedIPAddrBlocks Type

   ConstrainedIPAddrBlocks is a SEQUENCE OF one or more instances of
   ConstrainedIPAddressFamily.

   There MUST be only one instance of ConstrainedIPAddressFamily per
   unique Address Family Identifier (AFI).

   The elements of ConstrainedIPAddressFamily MUST be ordered by
   ascending addressFamily values (treating the octets as unsigned
   numbers).  Thus, when both IPv4 and IPv6 addresses are specified, the
   IPv4 addresses MUST precede the IPv6 addresses (since the IPv4 AFI of
   0001 is less than the IPv6 AFI of 0002).

   ConstrainedIPAddrBlocks is defined such that the resulting DER-
   encoded data are binary compatible with IPAddrBlocks defined in
   [RFC3779].

4.2.2.1.  ConstrainedIPAddressFamily Type

4.2.2.1.1.  addressFamily Field

   The addressFamily field is an OCTET STRING containing a 2-octet AFI,
   in network byte order.  Unlike IPAddrBlocks [RFC3779], a third octet
   containing a Subsequent Address Family Identifier (SAFI) MUST NOT be
   present.  AFIs are specified in the "Address Family Numbers" registry
   [IANA.ADDRESS-FAMILY-NUMBERS] maintained by IANA.

4.2.2.1.2.  addressesOrRanges Field

   The addressesOrRanges element is a SEQUENCE OF one or more
   IPAddressOrRange values, as defined in [RFC3779].  The rules for
   canonicalization and encoding defined in Section 2.2.3.6 of [RFC3779]
   apply to the value of addressesOrRanges.

4.3.  digestAlgorithm

   The digest algorithm is used to create the message digest of the
   attested digital object(s).  This algorithm MUST be a hashing
   algorithm defined in [RFC7935].

4.4.  checkList

   This field is a SEQUENCE OF one or more FileNameAndHash values.
   There is one FileNameAndHash entry for each digital object referenced
   on the RSC.

4.4.1.  FileNameAndHash

   Each FileNameAndHash is an ordered pair of the name of the directory
   entry containing the digital object and the message digest of the
   digital object.

   The hash field is mandatory.  The value of the hash field is the
   calculated message digest of the digital object.  The hashing
   algorithm is specified in the digestAlgorithm field.

   The fileName field is OPTIONAL.  This is to allow RSCs to be used in
   a "stand-alone" fashion in which nameless digital objects are
   addressed directly through their respective message digest rather
   than through a file system abstraction.

   If the fileName field is present, then its value:

   *  MUST contain only characters specified in the Portable Filename
      Character Set as defined in [POSIX].

   *  MUST be unique with respect to the other FileNameAndHash elements
      of checkList for which the fileName field is also present.

   Conversely, if the fileName field is omitted, then the value of the
   hash field MUST be unique with respect to the other FileNameAndHash
   elements of checkList for which the fileName field is also omitted.

5.  RSC Validation

   Before a Relying Party (RP) can use an RSC to validate a set of
   digital objects, the RP MUST first validate the RSC.  To validate an
   RSC, the RP MUST perform all the validation checks specified in
   [RFC6488], except for checking for the presence of an SIA extension,
   which MUST NOT be present in the EE certificate (see Section 2).  In
   addition, the RP MUST perform the following RSC-specific validation
   steps:

   1.  The contents of the CMS eContent field MUST conform to all of the
       constraints described in Section 4, including the constraints
       described in Section 4.4.1.

   2.  If the asID field is present within the contents of the resources
       field, then the AS identifier delegation extension [RFC3779] MUST
       be present in the EE certificate contained in the CMS
       certificates field.  The AS identifiers present in the eContent
       resources field MUST be a subset of those present in the
       certificate extension.  The EE certificate's AS identifier
       delegation extension MUST NOT contain "inherit" elements.

   3.  If the ipAddrBlocks field is present within the contents of the
       resources field, then the IP address delegation extension
       [RFC3779] MUST be present in the EE certificate contained in the
       CMS certificates field.  The IP addresses present in the eContent
       resources field MUST be a subset of those present in the
       certificate extension.  The EE certificate's IP address
       delegation extension MUST NOT contain "inherit" elements.

6.  Verifying Files or Data Using RSC

   To verify a set of digital objects with an RSC:

   *  The RSC MUST be validated according to the procedure described in
      Section 5.  If the RSC cannot be validated, verification MUST
      fail.  This error SHOULD be reported to the user.

   *  For every digital object to be verified:

      1.  If the verification procedure is provided with a filename for
          the object being verified (e.g., because the user has provided
          a file system path from which to read the object), then
          verification SHOULD proceed in "filename-aware" mode.
          Otherwise, verification SHOULD proceed in "filename-unaware"
          mode.

          Implementations MAY provide an option to override the
          verification mode, for example, to ignore the fact that the
          object is to be read from a file.

      2.  The message digest MUST be computed from the file contents or
          data using the digest algorithm specified in the
          digestAlgorithm field of the RSC.

      3.  The digest computed in Step 2 MUST be compared to the value
          appearing in the hash field of all FileNameAndHash elements of
          the checkList field of the RSC.

          One or more FileNameAndHash elements MUST be found with a
          matching hash value; otherwise, verification MUST fail, and
          the error SHOULD be reported to the user.

      4.  If the mode selected in Step 1 is "filename-aware", then
          exactly one of the FileNameAndHash elements matched in Step 3
          MUST contain a fileName field value exactly matching the
          filename of the object being verified.

          Alternatively, if the mode selected in Step 1 is "filename-
          unaware", then exactly one of the FileNameAndHash elements
          matched in Step 3 MUST have the fileName field omitted.

          Otherwise, verification MUST fail, and the error SHOULD be
          reported to the user.

   Note that in the above procedure, not all elements of checkList
   necessarily need be used.  That is, it is not an error if the length
   of checkList is greater than the size of the set of digital objects
   to be verified.  However, in this situation, implementations SHOULD
   issue a warning to the user, allowing for corrective action to be
   taken if necessary.

7.  Operational Considerations

   When creating digital objects of a plain-text nature (such as ASCII,
   UTF-8, HTML, Javascript, and XML), converting such objects into a
   lossless compressed form is RECOMMENDED.  Distributing plain-text
   objects within a compression envelope (such as GZIP [RFC1952]) might
   help avoid unexpected canonicalization at intermediate systems (which
   in turn would lead to checksum verification errors).  Validator
   implementations are expected to treat a checksummed digital object as
   a string of arbitrary single octets.

   If a fileName field is present, but no digital object within the set
   of to-be-verified digital objects has a filename that matches the
   content of that field, a validator implementation SHOULD compare the
   message digest of each digital object to the value from the hash
   field of the associated FileNameAndHash and report matches to the
   user for further consideration.

8.  Security Considerations

   RPs are hereby warned that the data in an RSC is self-asserted.  When
   determining the meaning of any data contained in an RSC, RPs MUST NOT
   make any assumptions about the signer beyond the fact that it had
   sufficient control of the issuing CA to create the object.  These
   data have not been verified by the Certificate Authority (CA) that
   issued the CA certificate to the entity that issued the EE
   certificate used to validate the RSC.

   RPKI certificates are not bound to real-world identities; see
   [RFC9255] for an elaboration.  RPs can only associate real-world
   entities to Internet Number Resources by additionally consulting an
   exogenous authority.  RSCs are a tool to communicate assertions
   signed with Internet Number Resources and do not communicate any
   other aspect of the resource holder's business operations, such as
   the identity of the resource holder itself.

   RSC objects are not distributed through the RPKI repository system.
   From this, it follows that third parties who do not have a copy of a
   given RSC may not be aware of the existence of that RSC.  Since RSC
   objects use EE certificates but all other currently defined types of
   RPKI object profiles are published in public CA repositories, an
   observer may infer from discrepancies in the repository that RSC
   object(s) may exist.  For example, if a CA does not use random serial
   numbers for certificates, an observer could detect gaps between the
   serial numbers of the published EE certificates.  Similarly, if the
   CA includes a serial number on a Certificate Revocation List (CRL)
   that does not match any published object, an observer could postulate
   that an RSC EE certificate was revoked.

   Conversely, a gap in serial numbers does not imply that an RSC
   exists.  Nor does the presence in a CRL of a serial number unknown to
   the RP imply an RSC object exists: the implicitly referenced object
   might not be an RSC, it might have never been published, or it may
   have been revoked before it was visible to RPs.  In general, it is
   not possible to confidently infer the existence or non-existence of
   RSCs from the repository state without access to a given RSC.

   While a one-time-use EE certificate must only be used to generate and
   sign a single RSC object, CAs technically are not restricted from
   generating and signing multiple different RSC objects with a single
   key pair.  Any RSC objects sharing the same EE certificate cannot be
   revoked individually.

9.  IANA Considerations

9.1.  SMI Security for S/MIME CMS Content Type (1.2.840.113549.1.9.16.1)

   IANA has allocated the following in the "SMI Security for S/MIME CMS
   Content Type (1.2.840.113549.1.9.16.1)" registry:

             +=========+=======================+============+
             | Decimal | Description           | References |
             +=========+=======================+============+
             | 48      | id-ct-signedChecklist | RFC 9323   |
             +---------+-----------------------+------------+

                                 Table 1

9.2.  RPKI Signed Objects

   IANA has registered the OID for the RSC in the "RPKI Signed Objects"
   registry [RFC6488] as follows:

       +==================+============================+===========+
       | Name             | OID                        | Reference |
       +==================+============================+===========+
       | Signed Checklist | 1.2.840.113549.1.9.16.1.48 | RFC 9323  |
       +------------------+----------------------------+-----------+

                                  Table 2

9.3.  RPKI Repository Name Schemes

   IANA has added the Signed Checklist file extension to the "RPKI
   Repository Name Schemes" registry [RFC6481] as follows:

           +====================+==================+===========+
           | Filename Extension | RPKI Object      | Reference |
           +====================+==================+===========+
           | .sig               | Signed Checklist | RFC 9323  |
           +--------------------+------------------+-----------+

                                  Table 3

9.4.  SMI Security for S/MIME Module Identifier
      (1.2.840.113549.1.9.16.0)

   IANA has allocated the following in the "SMI Security for S/MIME
   Module Identifier (1.2.840.113549.1.9.16.0)" registry:

        +=========+=================================+============+
        | Decimal | Description                     | References |
        +=========+=================================+============+
        | 73      | id-mod-rpkiSignedChecklist-2022 | RFC 9323   |
        +---------+---------------------------------+------------+

                                 Table 4

9.5.  Media Types

   IANA has registered the media type "application/rpki-checklist" in
   the "Media Types" registry as follows:

   Type name:  application

   Subtype name:  rpki-checklist

   Required parameters:  N/A

   Optional parameters:  N/A

   Encoding considerations:  binary

   Security considerations:  Carries an RPKI Signed Checklist.  This
      media type contains no active content.  See Section 5 of RFC 9323
      for further information.

   Interoperability considerations:  N/A

   Published specification:  RFC 9323

   Applications that use this media type:  RPKI operators

   Fragment identifier considerations:  N/A

   Additional information:

      Content:  This media type is a signed object, as defined in
         [RFC6488], which contains a payload of a list of checksums as
         defined in RFC 9323.
      Magic number(s):  N/A
      File extension(s):  .sig
      Macintosh file type code(s):  N/A

   Person & email address to contact for further information:  Job
      Snijders (job@fastly.com)

   Intended usage:  COMMON

   Restrictions on usage:  N/A

   Author:  Job Snijders (job@fastly.com)

   Change controller:  IETF

10.  References

10.1.  Normative References

   [POSIX]    IEEE and The Open Group, "Base Specifications", Issue 7,
              DOI 10.1109/IEEESTD.2016.7582338, 2016,
              <https://publications.opengroup.org/standards/unix/c165>.

   [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>.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <https://www.rfc-editor.org/info/rfc5652>.

   [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>.

   [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>.

   [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,
              <https://www.rfc-editor.org/info/rfc6488>.

   [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>.

   [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>.

   [RFC9286]  Austein, R., Huston, G., Kent, S., and M. Lepinski,
              "Manifests for the Resource Public Key Infrastructure
              (RPKI)", RFC 9286, DOI 10.17487/RFC9286, June 2022,
              <https://www.rfc-editor.org/info/rfc9286>.

10.2.  Informative References

   [IANA.ADDRESS-FAMILY-NUMBERS]
              IANA, "Address Family Numbers",
              <https://www.iana.org/assignments/address-family-numbers>.

   [RFC1952]  Deutsch, P., "GZIP file format specification version 4.3",
              RFC 1952, DOI 10.17487/RFC1952, May 1996,
              <https://www.rfc-editor.org/info/rfc1952>.

   [RFC6268]  Schaad, J. and S. Turner, "Additional New ASN.1 Modules
              for the Cryptographic Message Syntax (CMS) and the Public
              Key Infrastructure Using X.509 (PKIX)", RFC 6268,
              DOI 10.17487/RFC6268, July 2011,
              <https://www.rfc-editor.org/info/rfc6268>.

   [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>.

   [RFC9255]  Bush, R. and R. Housley, "The 'I' in RPKI Does Not Stand
              for Identity", RFC 9255, DOI 10.17487/RFC9255, June 2022,
              <https://www.rfc-editor.org/info/rfc9255>.

   [RPKI-RTA] Michaelson, G., Huston, G., Harrison, T., Bruijnzeels, T.,
              and M. Hoffman, "A profile for Resource Tagged
              Attestations (RTAs)", Work in Progress, Internet-Draft,
              draft-ietf-sidrops-rpki-rta-00, 17 January 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-sidrops-
              rpki-rta-00>.

   [signify]  Unangst, T. and M. Espie, "signify - cryptographically
              sign and verify files", <https://man.openbsd.org/signify>.

Acknowledgements

   The authors wish to thank George Michaelson, Geoff Huston, Randy
   Bush, Stephen Kent, Matt Lepinski, Rob Austein, Ted Unangst, and Marc
   Espie for prior art.  The authors thank Russ Housley for reviewing
   the ASN.1 notation and providing suggestions.  The authors would like
   to thank Nimrod Levy, Tim Bruijnzeels, Alberto Leiva, Ties de Kock,
   Peter Peele, Claudio Jeker, Theo Buehler, Donald Eastlake 3rd, Erik
   Kline, Robert Wilton, Roman Danyliw, √Čric Vyncke, Lars Eggert, Paul
   Wouters, and Murray S. Kucherawy for document review and suggestions.

Authors' Addresses

   Job Snijders
   Fastly
   Amsterdam
   Netherlands
   Email: job@fastly.com


   Tom Harrison
   Asia Pacific Network Information Centre
   6 Cordelia St
   South Brisbane QLD 4101
   Australia
   Email: tomh@apnic.net


   Ben Maddison
   Workonline Communications
   Cape Town
   South Africa
   Email: benm@workonline.africa