The browser sends a prefix (first few bytes) of the hash [1], and gets back a list of full hashes to compare locally. This is called k-anonymity, and it's good

The browser sends a prefix (first few bytes) of the hash [1], and gets back a list of full hashes to compare locally. This is called k-anonymity, and it's good enough for even services like Have I Been Pwned to use it for password lookups [2] [1] https://www.chromium.org/developers/design-documents/safebrowsing https://www.chromium.org/developers/design-documents/safebro... [2] https://blog.cloudflare.com/validating-leaked-passwords-with-k-anonymity/ https://blog.cloudflare.com/validating-leaked-passwords-with...