Question

I m trying to convert this piece of code from PHP to C#. It s part of a Captive Portal. Could somebody explain what it does?

  $hexchal = pack ("H32", $challenge);
  if ($uamsecret) {
    $newchal = pack ("H*", md5($hexchal . $uamsecret));
  } else {
    $newchal = $hexchal;
  }
  $response = md5("" . $password . $newchal);
  $newpwd = pack("a32", $password);
  $pappassword = implode ("", unpack("H32", ($newpwd ^ $newchal)));

Answer 1

Eduardo,

if you take a look at the pack manual, pack is used to convert a string in (hex, octal, binary )to his number representation.

so

$hexcal = pack( H32 , $challenge);

would convert a string like cca86bc64ec5889345c4c3d8dfc7ade9 to the actual 0xcca... de9

if $uamsecret exist do the same things with the MD5 of hexchal concacteate with the uamsecret. if ($uamsecret) { $newchal = pack ("H*", md5($hexchal . $uamsecret)); } else { $newchal = $hexchal; }

$response = md5("" . $password . $newchal);

MD% + $password + $newchal

$newpwd = pack("a32", $password);

pad password to 32 byte

  $pappassword = implode ("", unpack("H32", ($newpwd ^ $newchal)));

do a xor newpwd and newchal and convert it to a hexadecimal string, I don t get the implode() maybe it s to convert to string to an array of character.

Answer 2

I also encountered the need of php s pack-unpack functions in c# but did not get any good resource.

So i thought to do it myself. I have verified the function s input with pack/unpack/md5 methods found at onlinephpfunctions.com. Since i have done code only as per my requirements. This can be extended for other formats

Pack

    private static string pack(string input)
    {
        //only for H32 & H*
        return Encoding.Default.GetString(FromHex(input));
    }
    public static byte[] FromHex(string hex)
    {
        hex = hex.Replace("-", "");
        byte[] raw = new byte[hex.Length / 2];
        for (int i = 0; i < raw.Length; i++)
        {
            raw[i] = Convert.ToByte(hex.Substring(i * 2, 2), 16);
        }
        return raw;
    }

MD5

    private static string md5(string input)
    {
        byte[] asciiBytes = Encoding.Default.GetBytes(input);
        byte[] hashedBytes = MD5CryptoServiceProvider.Create().ComputeHash(asciiBytes);
        string hashedString = BitConverter.ToString(hashedBytes).Replace("-", "").ToLower();
        return hashedString;
    }

Unpack

    private static string unpack(string p1, string input)
    {
        StringBuilder output = new StringBuilder();

        for (int i = 0; i < input.Length; i++)
        {
            string a = Convert.ToInt32(input[i]).ToString("X");
            output.Append(a);
        }

        return output.ToString();
    }

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