  Integrity and trust on the web build on X.509 certificates. Misuse or
misissuance of these certificates threaten the Web PKI security model, which
led to the development of several guarding techniques. In this paper, we study
the DNS/DNSSEC records CAA and TLSA as well as CT logs from the perspective of
the certificates in use. Our measurements comprise 4 million popular domains,
for which we explore the existence and consistency of the different extensions.
Our findings indicate that CAA is almost exclusively deployed in the absence of
DNSSEC, while DNSSEC protected service names tend to not use the DNS for
guarding certificates. Even though mainly deployed in a formally correct way,
CAA CA-strings tend to not selectively separate CAs, and numerous domains hold
certificates beyond the CAA semantic. TLSA records are repeatedly poorly
maintained and occasionally occur without DNSSEC.
