Question

I’d like to use Portable PHP password hashing framework to hash passwords. But I find that its demos don’t use salt for hashing a password. But it use a dummy salt for checking password which I find it strange and I don’t understand this idea at all,

$dummy_salt = '$2a$08$1234567890123456789012';

if (isset($dummy_salt) && strlen($hash) < 20)
        $hash = $dummy_salt;

I wonder, if I want to use convention method which I can generate the unique salt and store it for each user in my database, how can I use Portable PHP password hashing framework to generate salts?

This is the function I use to hash passwords but I have been told that sha512 has the same issue as sha1, wise to trust the expert like Portable PHP password hashing framework,

function hash_sha512($phrase,&$salt = null)
{
    //$pepper = '!@#$%^&*()_+=-{}][;";/?<>.,';

    if ($salt == '')
    {
        $salt = substr(hash('sha512',uniqid(rand(), true).PEPPER_KEY.microtime()), 0, SALT_LENGTH);
    }
    else
    {
        $salt = substr($salt, 0, SALT_LENGTH);
    }

    return hash('sha512',$salt.PEPPER_KEY.$phrase);
}

Let me know if you have any idea. Thanks.

Answer 1

From the phpass article linked to from that page:

Besides the actual hashing, phpass
transparently generates random salts
when a new password or passphrase is
hashed, and it encodes the hash type,
the salt, and the password stretching
iteration count into the “hash
encoding string” that it returns. When
phpass authenticates a password or
passphrase against a stored hash, it
similarly transparently extracts and
uses the hash type identifier, the
salt, and the iteration count out of
the “hash encoding string”. Thus, you
do not need to bother with salting and
stretching on your own – phpass takes
care of these for you.

…so it’s not surprising that the examples don’t use salting! You may be over-seasoning your code.

The code sample with the dummy salt is an example of how to prevent a timing attack by making sure that whether a user exists or not, the validation of the user takes the same amount of time, effectively by doing a dummy authentication for non-existent users. It needs a dummy salt because if the user doesn’t exist, it won’t have a stored salt to use.