How to create md5 hash as the crypt function generates with a md5 salt using the md5 function, not the crypt function?

Question

I prefer using crypt function in php for password encryption and other one way encryption requirements. Because I can use any supported encryption algorithm, by changing the salt and there are few other advantages. Normally, I don't use any salt and it takes a random MD5 salt. I save this encryption string as password hash on the database, and while authenticating the user, I use this as salt to the crypt function. It works fine in php. But when it's needed any other programing language to create a hash, while I am using crypt function in the php part of the function, we were into problem.

I would like to know whether is there any simple way to create a MD5 hash (using PHP md5() function or other), which need to be similar to what crypt function generates while using a MD5 salt. If I can understand how it works in php, without using crypt function, then there may be a good possibility to implement in other programing languages.

Answer 1

Here's code in Java that implements the same function. This may help you to do the same in other languages.

For PHP, you may want to look into this code:

    echo 'MD5:          ' . crypt('mypassword', '$1$somesalt$') . "\n";
    echo 'MD5:          ' . mycrypt('mypassword', 'somesalt') . "\n";

    function to64($s, $n)
    {
        $i64 = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
        $r = '';
        while (--$n >= 0) {
            $ss = $s & 0x3f;
            $r .= $i64[$s & 0x3f];
            $s >>= 6;
         }
        return $r;
    }

    function mycrypt($v, $s) {
            $m = hash_init("md5");
            hash_update($m, $v);
            hash_update($m, '$1$');
            hash_update($m, $s);

            $m1 = hash_init("md5");
            hash_update($m1, $v);
            hash_update($m1, $s);
            hash_update($m1, $v);
            $final = hash_final($m1, true);
            for ($pl = strlen($v); $pl>0; $pl-=16) {
                    hash_update($m, substr($final, 0, $pl > 16? 16:$pl));
            }
            $final = "\0";
            for($i=strlen($v);$i!=0;$i>>=1) {
                    if (($i & 1) != 0) {
                            hash_update($m, $final);
                    } else {
                            hash_update($m, $v[0]);
                   }
            }
            $final = hash_final($m, true);
            for($i=0;$i<1000;$i++) {
                $m1 = hash_init("md5");

                if(($i&1)) {
                    hash_update($m1, $v);
                } else {
                    hash_update($m1, $final);
                }
                if(($i%3)) {
                    hash_update($m1, $s);
                }
                if(($i%7)) {
                    hash_update($m1, $v);
                }
                if(($i&1)) {
                    hash_update($m1, $final);
                } else {
                    hash_update($m1, $v);
                }
                $final = hash_final($m1, true);
            }
            $l = '$1$'.$s.'$';
            $l .= to64(ord($final[ 0])<<16 | (ord($final[ 6])<<8) | ord($final[12]), 4);
            $l .= to64(ord($final[ 1])<<16 | (ord($final[ 7])<<8) | ord($final[13]), 4);
            $l .= to64(ord($final[ 2])<<16 | (ord($final[ 8])<<8) | ord($final[14]), 4);
            $l .= to64(ord($final[ 3])<<16 | (ord($final[ 9])<<8) | ord($final[15]), 4);
            $l .= to64(ord($final[ 4])<<16 | (ord($final[10])<<8) | ord($final[ 5]), 4);
            $l .= to64(ord($final[11]), 2);

            return $l;
    }