public
Last active

How to use bcrypt in PHP to safely store passwords (PHP 5.3+ only)

  • Download Gist
bcrypt.php
PHP
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
<?php
 
// secure hashing of passwords using bcrypt, needs PHP 5.3+
// see http://codahale.com/how-to-safely-store-a-password/
 
// salt for bcrypt needs to be 22 base64 characters (but just [./0-9A-Za-z]), see http://php.net/crypt
// just an example; please use something more secure/random than sha1(microtime) :)
$salt = substr(str_replace('+', '.', base64_encode(sha1(microtime(true), true))), 0, 22);
 
// 2a is the bcrypt algorithm selector, see http://php.net/crypt
// 12 is the workload factor (around 300ms on my Core i7 machine), see http://php.net/crypt
$hash = crypt('foo', '$2a$12$' . $salt);
 
// we can now use the generated hash as the argument to crypt(), since it too will contain $a2$12$... with a variation of the hash. No need to store the salt anymore, just the hash is enough!
var_dump($hash == crypt('foo', $hash)); // true
var_dump($hash == crypt('bar', $hash)); // false
 
?>

See http://www.openwall.com/phpass/ for examples of good random sources and base64 generation.

something more random than base64_encode(sha1(microtime(true), true))), 0, 22) would be:
Instead bin2hex(openssl_random_pseudo_bytes(22));
openssl_random_pseudo_bytes is the most secure prng available in most php distributions

So this is all you need? :) Great!

$blowfish_salt = bin2hex(openssl_random_pseudo_bytes(22));
$hash = crypt($_POST['password'], "$2a$12$".$blowfish_salt);
// Save the hash but no need to save the salt

if (crypt($_POST['password'], $hash) == $hash) {
    // Verified
}

Seems like you do need to save the salt. I can't get the two hashes to match otherwise. Would you recommend having a static salt instead of setting it dynamically and storing it in the database? That way, even if the database was compromised, the hacker would not be able to read the hashes without the salt which is inside your code.

@ nagarjun, the point of bcrypt and using blowfish ($2a$) is that you set a work factor high enough where it would take someone a very long time to crack a single password even though they have the salt and the final hash right there.

A single static salt that all users would share makes the whole storage mechanism less secure. A random salt per user, with a high enough work factor, is all you need.

Please sign in to comment on this gist.

Something went wrong with that request. Please try again.