Convert PHP code that create encryption key to c# MD5

Question

I'm trying to convert the following code that create encryption key to c# the result I need the $key ** and ** $iv

$passphrase = 'asdfghjkl';
$salt =  '123456789' // for test purposes I fixed the value but it should be openssl_random_pseudo_bytes(8);
        $salted = '';
        $dx = '';
        while (strlen($salted) < 48) {
            $dx = md5($dx . $passphrase . $salt, true);
            $salted .= $dx;
        }
        $key = substr($salted, 0, 32);
        $iv = substr($salted, 32, 16);

what I could do until now

string passphrase = "asdfghjkl";
string salt = "123456789";
string key, iv;

byte[] salted = new byte[0];
byte[] dx = new byte[0];

while (salted.Length < 48)
      {
        string a = passphrase + salt;
        byte[] b = Encoding.UTF8.GetBytes(a);

        byte[] rv = new byte[dx.Length + b.Length];
        System.Buffer.BlockCopy(dx, 0, rv, 0, dx.Length);
        System.Buffer.BlockCopy(b, 0, rv, dx.Length, b.Length);

        //dx = MD5CryptoServiceProvider.Create().ComputeHash(rv);
        using (MD5 md5 = MD5.Create())
              {
                dx = md5.ComputeHash(rv);
              }

        byte[] rx = new byte[salted.Length + dx.Length];
        System.Buffer.BlockCopy(salted, 0, rx, 0, salted.Length);
        System.Buffer.BlockCopy(dx, 0, rx, salted.Length, dx.Length);

        salted = rx;
      }
string utfString1 = Encoding.UTF8.GetString(salted);
key = utfString1.Substring( 0, 32);
iv = utfString1.Substring(32, 16);

but I'm not getting the same result

thanks

That's a very inefficient way to create a salt and key. Do you have to do it this way? — John Conde
– John Conde, Commented Jul 16, 2020 at 12:14
unfortunately I have to do it this way, I have to talk to another system using this hashing — Iyad Bacdounes
– Iyad Bacdounes, Commented Jul 16, 2020 at 12:17
that's usually an encoding issue. check what your php is using. plus: md5 is not secure! it's been cracked for decades. plus: in php, you should not hash passwords yourself, but use passwod_hash() and password_verify(). — Franz Gleichmann
– Franz Gleichmann, Commented Jul 16, 2020 at 12:21
@JohnConde: Since this is key derivation from a password it should be slow. This is actually much too fast. Something standard like PBKDF2 is a much better choice. — President James K. Polk
– President James K. Polk, Commented Jul 16, 2020 at 13:52
@FranzGleichmann & JohnConde you both are correct, but I don't have the power to change the php code I just need to convert it into c# so I can connect to the system — Iyad Bacdounes
– Iyad Bacdounes, Commented Jul 16, 2020 at 14:15

Denys Vega · Accepted Answer · 2020-07-16 13:11:58Z

1

The called PHP md5 function will return the md5 hash in raw binary format (16 bytes). Read more about PHP md5.

Here is the equivalent in .NET.

...
var passphrase = Encoding.UTF8.GetBytes("asdfghjkl");
var salt = Encoding.UTF8.GetBytes("123456789");
var salted = new List<byte>();
var dx = new byte[0];
using (var md5 = MD5.Create())
{
    do
    {
        var bytesToHash = dx.Concat(passphrase).Concat(salt);
        dx = md5.ComputeHash(bytesToHash.ToArray());
        salted.AddRange(dx);
    } while (salted.Count < 48);
}

var key = salted.Take(32).ToArray();
var iv = salted.Skip(32).Take(16).ToArray();
...

If you want to check the outputs, use the PHP base64_encode function and the .NET Convert.ToBase64String, then compare the base64 strings.

answered Jul 16, 2020 at 13:11

Denys Vega

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