[cabfpub] CAA Proposal

Phillip philliph at comodo.com
Fri Jun 7 16:10:17 UTC 2013

Following up on the CAA threads, I would like to propose the following (subject to discussion):

1) CABForum endorse the publication of CAA records by domain name owners to mitigate the risk of issue of certificates in response to an unauthorized or fraudulent request.

2) The Basic requirements be updated to add a requirement that CAs state their policy for use of CAA records in their CPS.

"A CA MUST state its policy for processing CAA records as defined in RFC 6844"



To be compliant with the RFC, a CA MUST comply with the requirements of section 4:

Before issuing a certificate, a compliant CA MUST check for
   publication of a relevant CAA Resource Record set.  If such a record
   set exists, a CA MUST NOT issue a certificate unless the CA
   determines that either (1) the certificate request is consistent with
   the applicable CAA Resource Record set or (2) an exception specified
   in the relevant Certificate Policy or Certification Practices
   Statement applies.

A CA can be minimally compliant with the specification by simply publishing a statement that says that they retrieve and process CAA records for each request and then grant an automatic exception in every case.

This is deliberate because there is a peculiar edge case in which the Domain Name owner does not control their DNS publication infrastructure and the party that does inserts a spurious CAA record to limit competition. It also avoided the need for theological debates on what is and is not a public delegation point.

The point of CAA is to benefit CAs by reducing the cost of detecting potential fraudulent applications and mitigating the risk of issuing a certificate. But as with any other validation check, the response to a request that is non-consistent is not going to be to kick the request back to manual processing. There is going to be a person in the loop making enquiries. Either the CAA record is spurious and the CA wants to get it changed so that they can take the business or they have just detected an unauthorized request which they are going to want to look at an analyze and study.

A CA could write a CPS statement that says they look at CAA records and then ignore them completely but that would not look good. I think it rather more likely that it would say something like they have some sort of process for determining that CAA records do not represent the intention of the Domain Owner and publish a list of domains they will ignore CAA records from. This might include top-level domains like .com etc. But the fact that CAs have the option of ignoring the CAA records is probably sufficient to deter an attack.
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