public class reg
{
    public void write(string key, string valueName, string value)
    {
        Byte[] byteValue = System.Text.Encoding.UTF8.GetBytes(value);

        Registry.SetValue(key, valueName, value, RegistryValueKind.Binary);
    }
}

string key = @"HKEY_CLASSES_ROOT.sgdk2";
string valueName = string.Empty; // "(Default)" value
string value = "sgdk2file";

Microsoft.Win32.Registry.SetValue(key,valueName, value,
   Microsoft.Win32.RegistryValueKind.String);

static byte[] HexToBin(string hex)
{
   var result = new byte[hex.Length/2];
   for (int i = 0; i < hex.Length; i += 2)
   {
      result[i / 2] = byte.Parse(hex.Substring(i, 2), System.Globalization.NumberStyles.HexNumber);
   }
   return result;
}

static string BytesToHex(byte[] bytes)
{
   System.Text.StringBuilder sb = new StringBuilder();
   for (int i = 0; i < bytes.Length; i++)
   {
      sb.Append(bytes[i].ToString("x2"));
   }
   return sb.ToString();
}

static void Main(string[] args)
{
   byte[] bytes = HexToBin("0eff10");
   Console.WriteLine(BytesToBinaryString(bytes));
}

static byte[] HexToBin(string hex)
{
   var result = new byte[hex.Length / 2];
   for (int i = 0; i < hex.Length; i += 2)
   {
      result[i / 2] = byte.Parse(hex.Substring(i, 2), System.Globalization.NumberStyles.HexNumber);
   }
   return result;
}

static string BytesToBinaryString(byte[] bytes)
{
   var ba = new System.Collections.BitArray(bytes);
   System.Text.StringBuilder sb = new StringBuilder();
   for (int i = 0; i < ba.Length; i++)
   {
      int byteStart = (i / 8) * 8;
      int bit = 7 - i % 8;
      sb.Append(ba[byteStart + bit] ? '1' : '0');
      if (i % 8 == 7)
         sb.Append(' ');
   }
   return sb.ToString();
}

string valueString = "this is my test string";
byte[] value = System.Text.Encoding.ASCII.GetBytes(valueString);
Microsoft.Win32.Registry.SetValue(keyName, valueName, valueString, Microsoft.Win32.RegistryValueKind.Binary);