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Pretty sure CAA is supposed to be enforced by CAs, not by browsers. So, for instance, Let's Encrypt should refuse to issue a cert for your domain if you have CA
by mmalone 6y ago
Pretty sure CAA is supposed to be enforced by CAs, not by browsers. So, for instance, Let's Encrypt should refuse to issue a cert for your domain if you have CAA setup for digicert.
- JonathonW 6y agoCAA records (which specify which CAs are allowed to issue certificates for a given domain) are intended to be enforced by CAs, not by browsers. This prevents unintentional misissuance of a certificate, but not deliberate MITM attempts if the CA is actively involved. Their counterpart for browsers are TLSA records, which associate specific keys or certificates with a domain name. This is the part that actually prevents MITM attacks on the client side (assuming the client's getting a complete and accurate DNS response, which is a whole other issue), since it'll cause a compliant client to reject any other keys or certificates. (No idea how widespread the implementation of this is on the client side, though.)
- mmalone 6y agoNeat. I had never heard of TLSA. I’ll also add that certificate transparency (CT) is another mechanism designed to mitigate malicious cert issuance by a CA. A CT log is an public, append-only data structure. It doesn’t actively prevent anything, but it does ensure that a malicious issuance is easily detectable. In practice it seems to be a pretty effective deterrent against nation-state attacks: they won’t go undetected for long.