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Password Breach Checker
Check whether a password appears in a known data breach, without ever sending it anywhere. Your browser hashes it and sends only the first five characters of that hash.
How this stays private: your browser computes the SHA-1 hash and sends only the first five characters. The service returns every breached hash sharing that prefix - hundreds of them - and the match happens back in your browser. This is called k-anonymity, and it means nobody on the wire or at either end learns your password.