[cabf_validation] Section 7.1.2.10.5 CA Certificate Certificate Policies for cross signing certificates

[Paul van Brouwershaven]

We would like to clarify the following requirement in section 7.1.2.10.5 CA Certificate Certificate Policies, specifically for cross signing certificates.

RFC 5280 states that you can have one CertPolicyId within the PolicyInformation, see below:

certificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation

PolicyInformation ::= SEQUENCE {
        policyIdentifier   CertPolicyId,
        policyQualifiers   SEQUENCE SIZE (1..MAX) OF
                                PolicyQualifierInfo OPTIONAL }

CertPolicyId ::= OBJECT IDENTIFIER

Section 7.1.2.10.5 of the TLS BR states for the policyIdentifier:

The CA MUST include at least one Reserved Certificate Policy Identifier (see Section 7.1.6.1) associated with the given Subscriber Certificate type (see Section 7.1.2.7.1) directly or transitively issued by this Certificate.

This 'at least one' seems to contradict RFC 5280 which indicates that we can only have one policyIdentifier in the PolicyInformation sequence.

Then at the bottom of this section the TLS BRs states that entire certificate policies extension MUST contain exactly one Reserved Certificate Policy Identifier:

Regardless of the order of PolicyInformation values, the Certificate Policies extension MUST contain exactly one Reserved Certificate Policy Identifier.

While we can repeat the PolicyInformation within the certificatePolicies extension does this mean that CAs are prohibited from issuing a cross signing certificate (from a multi-purpose root to another multi-purpose root) with policy contrains that include DV, OV and EV reserved certificate policy identifiers. If our reading of this section is correct, this would mean that CAs need to issue three seperate cross signing certificates in that case.

Paul



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