hash() vs. crypt() function comparison

Question

I'm currently implementing a login system. I want to store the password and the salt in a database. Now I found out that there is a hash() and a crypt() function which seems to do the same (valid for SHA512).

hash() is newer and seems to support more hashing alogrithms than crypt(). Or there any other differences I should know/care about?

Edit:

function generatePasswordHash($password){
    $salt = base64_encode(mcrypt_create_iv(8));
    $calculatedPasswordHash = crypt($password, '$1$' . $salt . '$');

    return $calculatedPasswordHash;
}

The result looks like $1$Qh6ByGJ9$zLn3yq62egvmc9D7SzA2u.

Here my password checking function:

function checkLoginData($username, $password){
    global $db;

    $sql = "SELECT * FROM users WHERE username = :username";
    $result = $db->ExecuteQuery($sql, array("username"=>$username));

    if(!empty($result)){
        $result = $result[0];
        $savedPasswordHash = $result['password'];
        $splitted = explode("$", $savedPasswordHash);
        $salt = $splitted[2];
        $calculatedPasswordHash = crypt($password, '$1$' . $salt . '$');

        if($savedPasswordHash === $calculatedPasswordHash){
            return true;
        }
    }

    return false;
}

Shelter

@CodeInChaos: Storing and accessing password hashes from the database. Both can take a salt (add salt to $data parameter of hash() through concatenation). – Shelter

Just concatenating the salt to the data is insecure in many cases. Don't do that, unless you really know what you're doing. It's also fast and you want it to be slow. – Giga

The new code encrypts the password, instead of hashing it. i.e. its trivially reversible. – Giga

@CodeInChaos: So using mcrypt() is the wrong way? Here are the available encryption functions. Don't see MD5, SHA1, SHA2 here ... Seems crypt with MD5 is my only option. – Shelter

The md5 crypt scheme is decent. bcrypt is better, but I don't see any glaring issues in with md5 crypt. (Using a plain md5 hash on the other hand is a really bad idea) – Giga

@CodeInChaos: Did I get this right? With "MD5 crypt" MD5 with salt is meant? – Shelter

No, I mean the crypt function in CRYPT_MD5 mode. Not simply md5(data+salt). Single iteration md5 sucks, even with salt. – Giga

@CodeInChaos: Yes, I meant CRYPT_MD5. Thanks for clarifying that point again. See my edited question, which should do that. – Shelter

No idea what format mcrypt_create_iv returns. You might need to encode it before passing it to crypt. It's also recommended to use at least 64 bit salts. – Giga

Probably OK now. But as I said, I'm no php programmer. I also believe crypt returns the salt as part of its result, i.e. it's unnecessary to return/store the salt again. – Giga

@CodeInChaos: You are right. A part of the salt is returned, but not the whole one. I need to store the salt to check later the user input with the hash/salt stored in the database. – Shelter

If it returns only part of the salt, it's very likely that the rest of the salt gets ignored. – Giga

Answer 1

Use hash for hashing, for example in integrity checks. It directly uses the specified hashing algorithm.

crypt is a special purpose function. It's used for password hashing and key derivation. You'll need to pass in a salt, which indirectly determines the hashing scheme used. Even if you choose CRYPT_SHA512 this isn't plain SHA512. It's a key derivation function that uses SHA512 as building block. In particular such a scheme is deliberately slow(hider brute-force attacks) and combines salt and password in a secure way.

For password hashing in a log system, crypt is clearly the right choice.

Giga

Which function do you prefer to use for storing/retrieving password hashes? – Shelter

crypt with CRYPT_BLOWFISH and a high quality salt, from a crypto PRNG, such as mcrypt_create_iv should be fine. This requires php 5.3. But as I am no php programmer, I haven't looked into the details. – Giga

I found out that the webspace only provides Standard DES and MD5. I'll have a look into the mcrypt library ... – Shelter

Hey can someone please explain to me or edit this answer to provide information on the differences between hashing and using a cryptographic function, thank you! – Kela