yeosteve wrote:
SHA1 is just as easy to crack now, apparently. Salted SHA256 is the
way to go, perhaps something like
$pwd = $_POST['pwd'];
$salt = sha1(md5($pwd);
$encrypted = hash('sha256', $pwd.$salt);
Noone's going to be able to use a reverse lookup to get the original
password, if they do get into your database, and if anyone can see
your code to see how you mixed things up, you've lost anyway, but I'd
be interested to see how others do this.
Steve
Hi Steve,
That is not exactly true, switching your hash to one with less chance of
collisions is not actually improving security. The main problem is the
possibility of your code and database being compromised, with the above
code you can get a common-password dictionary and generate hashes using
your code for each dictionary word, giving the ability to find insecure
passwords in the database. As the above hash generation logic is
indentical for each interation (each password that is generated) you are
as 'safe' as if you were using a fixed salt. If your database is
compromised, a hacker would be able to create a dictionary of hashes
using a common-passwords dictionary and look for insecure passwords. If
your database contains a large number of users then you are guaranteed
to have compromised accounts.
A better method is to generate a unique one-time salt for each
interaction (each password) and storing this along with the password.
Each password hash is created with a unique salt, so if the password is
re-hashed or if a dictionary word is re-hashed, you cannot match them up.
Here is some simple code for achieving very good security:
$salt = substr(sha1(uniqid(mt_rand(), true)), -10); //Generate a 10
character salt
$password_hash = $salt . sha1($salt . $password); //Concatenate salt and
plain text password
Stored password is now 50 characters, 10 character salt and 40 character
hash.
Then to compare:
$salt = substr($password_hash, 0, 10); //Extract salt
if(sha1($salt . $compare_password) == substr($password_hash, 10))
{
return true;
}
This has the benefit of having a unique salt for each record, and having
the salt storage in the same field. It is also security through
obfuscation due to the uncommon length of the password hash (50
characters) and the inability to immediately see where the salt is stored.
Hope this helps!
Cheers,
Stig Manning
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