Hashing, the one-way fingerprint

New idea

How can a site check a password it doesn't know?

When you log in, the site checks that your password is right. But a well-built site never stores your password. So what is it comparing against?

The trick is a hash: a function that turns any input into a short fingerprint. The word hello always becomes 2cf24dba… (64 characters long with a popular hash called SHA-256).

Like a fingerprint, the hash is tiny compared with the thing it came from, and the same input always gives the same hash.