How to retrieve a REG_BINARY value from registry and convert to string

How to retrieve a REG_BINARY value from registry and convert to string

The code below is not working for me and I don't know why. (I have read
the 2 match in "Questions that may already have your answer" but didn't
help.)
I need to retrieve the unique number that Windows create for the C: drive
in the registry. The value is REG_BINARY and I need it in string. When I
said that the code doesn't work I meant it always return only 2 strange
characters when the key value is: 19 49 84 25 00 00 50 06 00 00 00 00 I
would prefer to have the original key value as a string
byte[] machineID =
(byte[])Microsoft.Win32.Registry.GetValue("HKEY_LOCAL_MACHINE\\SYSTEM\\MountedDevices",
"\\DosDevices\\C:", null);
if (machineID != null)
{
var str = System.Text.Encoding.Default.GetString(machineID);
MessageBox.Show(str);
}