| RFC 9323 | RPKI Signed Checklists (RSCs) | November 2022 |
| Snijders, et al. | Standards Track | [Page] |
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.¶
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 athttps://www.rfc-editor.org/info/rfc9323.¶
Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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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.¶
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.¶
RSC follows the Signed Object Template for the RPKI[RFC6488] with one exception: because RSCsMUST NOT be distributed through the global RPKI repository system, the Subject Information Access (SIA) extensionMUST 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.¶
The Certification Authority (CA)MUST only sign one RSC with each EE certificate andMUST generate a new key pair for each new RSC. This type of EE certificate is termed a "one-time-use" EE certificate (seeSection 3 of [RFC6487]).¶
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 OIDMUST appear within both the eContentType in the encapContentInfo object and the ContentType signed attribute in the signerInfo object (see[RFC6488]).¶
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 ::=BEGINIMPORTS 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 ConstrainedIPAddressFamilyConstrainedIPAddressFamily ::= SEQUENCE { addressFamily OCTET STRING (SIZE(2)), addressesOrRanges SEQUENCE (SIZE(1..MAX)) OF IPAddressOrRange }ConstrainedASIdentifiers ::= SEQUENCE { asnum [0] SEQUENCE (SIZE(1..MAX)) OF ASIdOrRange }END¶The version number of the RpkiSignedChecklistMUST be 0.¶
The resources contained here are the resources used to mark the attestation andMUST 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, itMUST contain an instance of ConstrainedASIdentifiers.¶
If the ipAddrBlocks field is present, itMUST contain an instance of ConstrainedIPAddrBlocks.¶
At least one of asID or ipAddrBlocksMUST 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, implementationsMUST NOT ignore errors resulting from the more restrictive definitions contained herein; in particular, such errorsMUST cause the validation procedure described inSection 5 to fail.¶
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].¶
ConstrainedIPAddrBlocks is a SEQUENCE OF one or more instances of ConstrainedIPAddressFamily.¶
ThereMUST be only one instance of ConstrainedIPAddressFamily per unique Address Family Identifier (AFI).¶
The elements of ConstrainedIPAddressFamilyMUST be ordered by ascending addressFamily values (treating the octets as unsigned numbers). Thus, when both IPv4 and IPv6 addresses are specified, the IPv4 addressesMUST 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].¶
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.¶
The addressesOrRanges element is a SEQUENCE OF one or more IPAddressOrRange values, as defined in[RFC3779]. The rules for canonicalization and encoding defined inSection 2.2.3.6 of [RFC3779] apply to the value of addressesOrRanges.¶
The digest algorithm is used to create the message digest of the attested digital object(s). This algorithmMUST be a hashing algorithm defined in[RFC7935].¶
This field is a SEQUENCE OF one or more FileNameAndHash values. There is one FileNameAndHash entry for each digital object referenced on the RSC.¶
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 isOPTIONAL. 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:¶
Conversely, if the fileName field is omitted, then the value of the hash fieldMUST be unique with respect to the other FileNameAndHash elements of checkList for which the fileName field is also omitted.¶
Before a Relying Party (RP) can use an RSC to validate a set of digital objects, the RPMUST first validate the RSC. To validate an RSC, the RPMUST perform all the validation checks specified in[RFC6488], except for checking for the presence of an SIA extension, whichMUST NOT be present in the EE certificate (seeSection 2). In addition, the RPMUST perform the following RSC-specific validation steps:¶
To verify a set of digital objects with an RSC:¶
For every digital object to be verified:¶
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 verificationSHOULD proceed in "filename-aware" mode. Otherwise, verificationSHOULD proceed in "filename-unaware" mode.¶
ImplementationsMAY provide an option to override the verification mode, for example, to ignore the fact that the object is to be read from a file.¶
The message digestMUST be computed from the file contents or data using the digest algorithm specified in the digestAlgorithm field of the RSC.¶
The digest computed in Step2MUST 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 elementsMUST be found with a matching hash value; otherwise, verificationMUST fail, and the errorSHOULD be reported to the user.¶
If the mode selected in Step1 is "filename-aware", then exactly one of the FileNameAndHash elements matched in Step3MUST contain a fileName field value exactly matching the filename of the object being verified.¶
Alternatively, if the mode selected in Step1 is "filename-unaware", then exactly one of the FileNameAndHash elements matched in Step3MUST have the fileName field omitted.¶
Otherwise, verificationMUST fail, and the errorSHOULD 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, implementationsSHOULD issue a warning to the user, allowing for corrective action to be taken if necessary.¶
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 isRECOMMENDED. 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 implementationSHOULD 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.¶
RPs are hereby warned that the data in an RSC is self-asserted. When determining the meaning of any data contained in an RSC, RPsMUST 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.¶
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 |
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 |
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 |
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 |
IANA has registered the media type "application/rpki-checklist" in the "Media Types" registry as follows:¶
The authors wish to thankGeorge Michaelson,Geoff Huston,Randy Bush,Stephen Kent,Matt Lepinski,Rob Austein,Ted Unangst, andMarc Espie for prior art. The authors thankRuss Housley for reviewing the ASN.1 notation and providing suggestions. The authors would like to thankNimrod Levy,Tim Bruijnzeels,Alberto Leiva,Ties de Kock,Peter Peele,Claudio Jeker,Theo Buehler,Donald Eastlake 3rd,Erik Kline,Robert Wilton,Roman Danyliw,Éric Vyncke,Lars Eggert,Paul Wouters, andMurray S. Kucherawy for document review and suggestions.¶