Storing passwords in salted hashes for user logins

Question

Possible Duplicate:
How do you use bcrypt for hashing passwords in PHP?

I am researching the best and safest methods of encrypting and storing user passwords in a database for logins. One article I came across, Salted Password Hashing - Doing it Right, provides a fairly complicated-looking set of functions for encrypting and checking passwords.

I understand how the code works, but the article also mentions storing not only the hashed password in the database, but the salt as well. How would I go about doing that, using the given code? For example:

// User registers with username and password; assume they're already validataed
$hash = create_hash($password_entered);
$password_hash = $hash[HASH_PBKDF2_INDEX];
$salt = $hash[HASH_SALT_INDEX];

$PDO = new PDO('mysql:host=localhost;dbname=myDatabase', $username, $password);
$statement = $PDO->prepare('INSERT INTO users (username, password, user_salt)
    VALUES (:username, :password; :user_salt)');
$statement->execute(array(
    ':username'  => $username_entered,
    ':password'  => $password_hash,
    ':user_salt' => $salt,
));

That seems right... however, when verifying a login, I'm not sure what to check against the entered password from the login form. The compiled hash returned by create_hash() gives a colon-delimited list of values. I'm just not sure where to go from here, or if this source code is even worth using.

If you are looking for the safest way. Don't do it yourself. Either wait till PHP 5.5 for the native password API or use [the compat lib](https://github.com/ircmaxell/password_compat) in the meantime. — PeeHaa, Dec 19 '12 at 21:29
Aren't you supposed to use the `validate_password` function from the article? And as you wrote, `create_hash` returns a string which already contains everything needed to recreate it (algorithm, iterations, hash and salt), so you only need to store that concatenated string. — vgru, Dec 19 '12 at 21:30
Looks like the `create_hash` function embeds the salt right with the hash (a common practice) so no need to store the salt separately on the user record. — Eric Petroelje, Dec 19 '12 at 21:31
How is this an exact duplicate of a question regarding `bcrypt`, which I've never HEARD of? What the hell kind of moderation is this, seriously? My question is regarding a completely different library of code than that other question. Whatever. — TerranRich, Dec 20 '12 at 02:21

score 1 · Accepted Answer · answered Dec 19 '12 at 21:33

I haven't used this code but I'm pretty sure you should not save user_salt separately in a column of your user table. User salt will be included in the hash (location 3 in a colon delimited hash). In your login script, get the password user has entered, and call the following function:

// here run a query and get the hashed password from the users table and put the
// hashed value in $hashed_password_from_database
// $user_enetered_password usually comes from $_POST

if (validate_password($user_entered_password, $hashed_password_from_database)) {
  // login successful
} else {
  // login failed
}

Ohh, I get it! When it mentions storing the salt in the database, it means the whole comma-delimited value that `create_hash()` generates. I get it now. Thanks! — TerranRich, Dec 19 '12 at 21:59

score 1 · Answer 2 · answered Dec 19 '12 at 21:34

To verify the login, use the following function, found on the link you posted, with $password being the password entered by the user attempting to log in, and $good_hash being PBKDF2_HASH_ALGORITHM . ":" . PBKDF2_ITERATIONS . ":" . $salt_from_db . ":" . $hash_from_db

function validate_password($password, $good_hash)
{
    $params = explode(":", $good_hash);
    if(count($params) < HASH_SECTIONS)
       return false;
    $pbkdf2 = base64_decode($params[HASH_PBKDF2_INDEX]);
    return slow_equals(
        $pbkdf2,
        pbkdf2(
            $params[HASH_ALGORITHM_INDEX],
            $password,
            $params[HASH_SALT_INDEX],
            (int)$params[HASH_ITERATION_INDEX],
            strlen($pbkdf2),
            true
        )
    );
}

Storing passwords in salted hashes for user logins

2 Answers2