(PHP) SHA1 vs md5 vs SHA256: which to use for a PHP login?

Question

I'm making a php login, and I'm trying to decide whether to use SHA1 or Md5, or SHA256 which I read about in another stackoverflow article. Are any of them more secure than others? For SHA1/256, do I still use a salt?

Also, is this a secure way to store the password as a hash in mysql?

function createSalt()
{
    $string = md5(uniqid(rand(), true));
    return substr($string, 0, 3);
}

$salt = createSalt();

$hash = sha1($salt . $hash);

Answer 1

Neither. If at all possible, you should use bcrypt. The hashes you mention are all optimized for speed and as such they are easily cracked. If you must use them, be sure to use a long salt and re-hash multiple times.

Answer 2

Use SHA256. It is not perfect, as SHA512 would be ideal, but out of the options, its the definite choice. As per any hashing technology, be sure to salt the hash for added security.

As an added note, FRKT, please show me where someone can easily crack a salted SHA256 hash? I am truly very interested to see this. SHA1 has been cracked, MD5 the same. SHA256 to my knowledge has still not been broken.

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Edit on Salting:

Use a random number, or random byte stream etc. You can use the unique field of the record in your database as the salt too, this way the salt is different per user.

Answer 3

Sorry, but is it possible to crack md5 hash? A thought, that it is pretty strong.

Answer 4

As FRKT pointed out, the post by Thomas Ptacek at chargen.matasano.com explains why simple, general-purpose hashing functions such as MD5, SHA1, SHA256 and SHA512 are poor password hashing choices.

Why? They are too fast--you can calculate 1,000,000 MD5 hashes a second per core with a modern computer, so brute force is feasible against most passwords people use.

Salting without key stretching only means that you cannot precompute the rainbow table, you need to build it ad hoc for that specific salt.

So the choice for PHP is either Crypt/Blowfish (BCrypt), Crypt/SHA256 or Crypt/SHA512. Or at least Crypt/MD5 (PHK). See www.php.net/manual/en/function.crypt.php

Answer 5

Out of this three algorythms the sha256 is way more safer, than the other two. But the good salting is much more important then the good choice of hash method.

You should use a fix salt, wich is long enough to prevent its cracking by brute force.

You should also use a random salt, wich can be stored as plain text in the db beside the hashed password. It can be quite short, it's main aim to prevent the attacker to find the common passwords(without random salt their hashes would be the same) and (if the attacker gets the fix salt) to prevent building site specific rainbow tables.

Sample code:

define('FIX_SALT','DVlDR%UZFdsf%!gfjSEFsz5ghdf');
(..)
$hashed_pass = hash('sha256',FIX_SALT.$plain_pass.$random_salt);

$random_salt should be a short random string, and can be stored as a plain text, as I mentioned above.

You shouldn't worry about the good speed of SHA256. There is no way that any attacker can generate even 2^128 hashes, it will be impossible in the next 20 years...