How Does bcrypt.compare() Verify Passwords with Random Salts?

The essential part is that bcrypt doesn't have to rehash without the original salt — it incorporates the salt into the hash string itself. During the comparison process, it simply extracts the stored salt from the hash, hashes the entered password with that salt, and checks if the hashes match.

In a bcrypt hash, the salt is included in the final hash format. When you want to compare the plaintext password to what’s in the database, bcrypt retrieves the salt from the stored hash (often found towards the end) and hashes the inputted password using that same salt, then it compares the two hashes.

Yes, you’ve got it! The compare function utilizes a hash string that already contains the salt combined with the hash and other information. So when you call `bcrypt.compare(password, storedHash)`, bcrypt extracts the salt from the hash and uses it to validate your password.

What you actually store in the database is a string combining the salt and the password hash, typically formatted as "hash:salt" or using a fixed length, where part of it is always the salt. This allows the bcrypt library to reclaim the salt when needed.

Yes, the salt is part of the hash result. Its purpose is to foil attempts to use pre-calculated hash tables. An attacker would need to pre-compute hashes for every possible salt combination, which is impractical. The salt can often be seen directly in the hash string and is usually between slashes (/?).