Policy Qualifiers in Resource Public Key Infrastructure (RPKI) Certificates

This document introduces policy qualifiers in the certificate policies extension of the RPKI resource certificates. This document updates . The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in .

profiles certificates, certificate revocation lists, and certificate signing requests specified in for use in routing public key infrastructure. defines an extension to certificates for the listing of policy information (see Section 4.2.1.4). states in Section 4.8.9: "This extension MUST be present and MUST be marked critical. It MUST include exactly one policy, as specified in the RPKI CP ". This references the CertPolicyId of the sequence allowed in PolicyInformation as defined by . also specifies that PolicyInformation may optionally have a sequence of PolicyQualifierInfo objects. does not specifically allow or disallow these PolicyQualifierInfo objects, although Section 4 also states: "Unless specifically noted as being OPTIONAL, all the fields listed here MUST be present, and any other fields MUST NOT appear in a conforming resource certificate." Because there is a need for some RPKI Certificate Authorities to include policy qualifiers in their certificates, this document updates Section 4.8.9 of as follows: OLD: This extension MUST be present and MUST be marked critical. It MUST include exactly one policy, as specified in the RPKI Certificate Policy (CP) . NEW: This extension MUST be present and MUST be marked critical. It MUST include exactly one policy, as specified in the RPKI CP . Exactly one policy qualifier MAY be included. If a policy qualifier is included, the policyQualifierId MUST be the Certification Practice Statement (CPS) pointer qualifier type (id-qt-cps). As noted in , Section 4.2.1.4: "Optional qualifiers, which MAY be present, are not expected to change the definition of the policy." In this case, any optional policy qualifier that MAY be present in a resource certificate MUST NOT change the definition of the RPKI CP .

The Security Considerations of apply to this document. This document updates the RPKI certificate profile to specify that the certificate policies extension can include a policy qualifier, which is a URI. While dereferencing the URI is not required for certificate validation, doing so could provide a denial-of-service (DoS) vector, where the target host may be subjected to bogus work dereferencing the URI. However, this specification, like , places no processing requirements on the URI included in the qualifier. As an update to , this document broadens the class of certificates that conform to the RPKI profile by explicitly including within the profile those certificates that contain a policy qualifier as described here. A relying party that performs a strict validation based on and fails to support the updates described in this document would incorrectly invalidate RPKI objects that include the changes in .

Frank Hill and Adam Guyot helped define the scope of the issue covered by this document and identified and worked with RPKI validator implementers to clarify the use of policy qualifiers in resource certificates. Sean Turner provided significant text to this document regarding the processing of the CPS URI and limiting the scope of the allowable content of the policy qualifier.