Right, so the hashing and comparison of hashes also can happen in the back end, and the API response can just be true/false whether it’s a match or not. That way the hashes and the hashing algorithm could all stay private.

The comparison API would of course also need its own rate limits and backoff etc to ensure it cannot be used to bruteforce attempts until you get a ‘true’ back.

All in all it’s a terrible idea though and nobody should actually do this.