Hash value always different on same input

Question

I'm trying to use this hashing function but each time I reload the page it gives me a different string, except for the first 7 characters.

<?php  
require("lib/password.php")  
$pass = $_POST['input_password'];
echo 'Received: '.$pass.'<br />';
$passwordHash = 'default';   
$passwordHash = password_hash(trim($pass), PASSWORD_DEFAULT, ["cost" => 11]);   
echo 'Password hash is '.$passwordHash;  

For example I pass over aaa and get the hashes

$2y$11$1Ll4twbmFNWhVxBOCeDWhOtZ4WchW.GYXK3LSH9BnW6AhXf45soWq
$2y$11$H0dmOkkq3rSgggDbGueRPusODmkZrrFqG7I/R1B0tFTQEYGHB0iZi
$2y$11$z0pFOoFsD5Bk0sx2TiT3kOd2awAwDBQAsQaxlDq11kNH.ldaS1qw2

I'm using WAMP Server 2.2 on Windows 7 64 bit and Firefox 17.

Answer 1

That hash algorithm uses a random salt each time. It's designed to be different each time, even with the same input.

To check passwords, use the password_verify function included in that library.

Note: The $2y$11$ at the beginning specifies the algorithm and cost used to generate the hash.