Storing Passwords Safely

A website must never store passwords as plain text: a database leak would expose every account, and people reuse passwords. Storing a plain fast hash is not enough either, because two users with the same password get the same digest and attackers hash billions of guesses per second.

The right way:

1. add a unique random salt to each password, so identical passwords give different digests;
2. use a deliberately slow password hash (PBKDF2, scrypt, bcrypt or Argon2) so each guess costs time;
3. store the salt and the digest, never the password.

To log in, hash the attempt with the stored salt and compare. Use a constant-time comparison, hmac.compare_digest, so timing does not leak information. The example uses the standard library's PBKDF2. Real sites use hundreds of thousands of iterations.