How do you set up Certificate Transparency monitoring that catches a rogue cert within hours?

How do you set up Certificate Transparency monitoring that catches a rogue cert within hours?

Because every publicly-trusted cert is logged (RFC 9162), CT turns the logs into a detection system for unauthorized issuance against your domains. A monitor you configure once is cheaper than discovering a mis-issued cert from an outage. Setup checklist.

— Enumerate the full set of names to watch: apex, every subdomain pattern, internationalized variants, and look-alike domains you own.
— Subscribe to a CT monitor (crt.sh RSS, Cert Spotter, or your own poller against the log Get-Entries endpoint) keyed on those names.
— Baseline the current legitimate certs so the monitor alerts on net-new issuance, not on your own renewals.
— Cross-reference each alert against your issuance records: a cert from a CA you never use, or for a hostname you never requested, is the signal.
— Account for the Maximum Merge Delay (typically 24h): a cert may exist before it appears in logs, so CT is near-real-time, not instant.

Evidence vs. speculation: CT proves a cert was issued, not that it is being used; pair alerts with DNS and traffic checks.

Further reading: RFC 9162 section 5 (log client messages); Cert Spotter and crt.sh documentation.

Bottom line: a name inventory plus a baseline turns CT logs from public record into an active alarm.