How to retrieve windows product key

To retrieve the windows product key you can use the following 
script in Powershell:

function get-windowsproductkey([string]$computer)

{

$Reg = [WMIClass] ("\\" + $computer + "\root\default:StdRegProv")

$values = [byte[]]($reg.getbinaryvalue(2147483650,"SOFTWARE\Microsoft\Windows NT\CurrentVersion","DigitalProductId").uvalue)

$lookup = [char[]]("B","C","D","F","G","H","J","K","M","P","Q","R","T","V","W","X","Y","2","3","4","6","7","8","9")

$keyStartIndex = [int]52;

$keyEndIndex = [int]($keyStartIndex + 15);

$decodeLength = [int]29

$decodeStringLength = [int]15

$decodedChars = new-object char[] $decodeLength

$hexPid = new-object System.Collections.ArrayList

for ($i = $keyStartIndex; $i -le $keyEndIndex; $i++){ [void]$hexPid.Add($values[$i]) }

for ( $i = $decodeLength - 1; $i -ge 0; $i--)

    {               

     if (($i + 1) % 6 -eq 0){$decodedChars[$i] = '-'}

     else

       {

        $digitMapIndex = [int]0

        for ($j = $decodeStringLength - 1; $j -ge 0; $j--)

        {

            $byteValue = [int](($digitMapIndex * [int]256) -bor [byte]$hexPid[$j]);

            $hexPid[$j] = [byte] ([math]::Floor($byteValue / 24));

            $digitMapIndex = $byteValue % 24;

            $decodedChars[$i] = $lookup[$digitMapIndex];

         }

        }

     }

$STR = ''   

$decodedChars | % { $str+=$_}

$STR

}

get-windowsproductkey .