Group Policy Preferences Decoder

GPPDecrypt.ps1

 param (
    [string]$cpassword    
 )

function Get-DecryptedCpassword {
        [CmdletBinding()]
        Param (
            [string] $Cpassword 
        )

        try {
            #Append appropriate padding based on string length  
            $Mod = ($Cpassword.length % 4)
            
            switch ($Mod) {
            '1' {$Cpassword = $Cpassword.Substring(0,$Cpassword.Length -1)}
            '2' {$Cpassword += ('=' * (4 - $Mod))}
            '3' {$Cpassword += ('=' * (4 - $Mod))}
            }

            $Base64Decoded = [Convert]::FromBase64String($Cpassword)
                        
            $AesObject = New-Object System.Security.Cryptography.AesCryptoServiceProvider
            # Public available AES key on https://msdn.microsoft.com/en-us/library/2c15cbf0-f086-4c74-8b70-1f2fa45dd4be.aspx?f=255&MSPPError=-2147217396
            [Byte[]] $AesKey = @(0x4e,0x99,0x06,0xe8,0xfc,0xb6,0x6c,0xc9,0xfa,0xf4,0x93,0x10,0x62,0x0f,0xfe,0xe8,
                                 0xf4,0x96,0xe8,0x06,0xcc,0x05,0x79,0x90,0x20,0x9b,0x09,0xa4,0x33,0xb6,0x6c,0x1b)
            
            $AesIV = New-Object Byte[]($AesObject.IV.Length) 
            $AesObject.IV = $AesIV
            $AesObject.Key = $AesKey
            $DecryptorObject = $AesObject.CreateDecryptor() 
            [Byte[]] $OutBlock = $DecryptorObject.TransformFinalBlock($Base64Decoded, 0, $Base64Decoded.length)
            
            return [System.Text.UnicodeEncoding]::Unicode.GetString($OutBlock)
        } 
        
        catch {
            Write-Error $Error[0]
            }
    }  

$decriptedpassword =  Get-DecryptedCpassword $cpassword 
write-host $decriptedpassword