Private/DecryptFile.ps1
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<#
.SYNOPSIS Decrypts a file using AES. .DESCRIPTION Decrypts a file using an AES key. .PARAMETER FileToDecrypt File(s) to be decrypted .PARAMETER Key AES key to be used for decryption. .EXAMPLE DecryptFile 'C:\file.ext.encrypted' $key This example decrypts C:\file.ext.encrypted with the key stored in the variable $key. .NOTES Author: Tyler Siegrist Date: 8/23/2016 https://gallery.technet.microsoft.com/scriptcenter/EncryptDecrypt-files-use-65e7ae5d #> Function DecryptFile { Param( [Parameter(Mandatory=$true, Position=1)] [System.IO.FileInfo[]]$FileToDecrypt, [Parameter(Mandatory=$true, Position=2)] [String]$Key, [Parameter(Mandatory=$false, Position=3)] [String]$Suffix ) #Load dependencies try { if ($PSVersionTable.PSEdition -eq "Core") { $SystemCoreAssemblyPath = $($(Get-Command pwsh).Source | Split-Path -Parent) + '\System.Core.dll' if (!$(Test-Path $SystemCoreAssemblyPath)) { Write-Error "The path '$SystemCoreAssemblyPath' was not found! Halting!" $global:FunctionResult = "1" return } $null = Add-Type -Path $SystemCoreAssemblyPath } else { [System.Reflection.Assembly]::LoadWithPartialName('System.Security.Cryptography') } } catch { Write-Error 'Could not load required assembly.' Return } #Configure AES try { $EncryptionKey = [System.Convert]::FromBase64String($Key) $KeySize = $EncryptionKey.Length*8 $AESProvider = New-Object 'System.Security.Cryptography.AesManaged' $AESProvider.Mode = [System.Security.Cryptography.CipherMode]::CBC $AESProvider.BlockSize = 128 $AESProvider.KeySize = $KeySize $AESProvider.Key = $EncryptionKey } catch { Write-Error 'Unable to configure AES, verify you are using a valid key.' Return } #Used to store successfully decrypted file names. $DecryptedFiles = @() $FailedToDecryptFiles = @() foreach ($File in $FileToDecrypt) { # Try to decrypt as long as the .decrypted file doesn't already exist $DestinationFile = "$($File.FullName).decrypted" if (!$(Test-Path $DestinationFile)) { #Open file to decrypt try { $FileStreamReader = New-Object System.IO.FileStream($File.FullName, [System.IO.FileMode]::Open) } catch { Write-Error "Unable to open $($File.FullName) for reading." Continue } #Create destination file try { $FileStreamWriter = New-Object System.IO.FileStream($DestinationFile, [System.IO.FileMode]::Create) } catch { $FileStreamReader.Close() $FileStreamWriter.Close() Remove-Item $DestinationFile -Force Write-Error "Unable to open $DestinationFile for writing." Continue } #Get IV try { [Byte[]]$LenIV = New-Object Byte[] 4 $FileStreamReader.Seek(0, [System.IO.SeekOrigin]::Begin) | Out-Null $FileStreamReader.Read($LenIV, 0, 3) | Out-Null [Int]$LIV = [System.BitConverter]::ToInt32($LenIV, 0) [Byte[]]$IV = New-Object Byte[] $LIV $FileStreamReader.Seek(4, [System.IO.SeekOrigin]::Begin) | Out-Null $FileStreamReader.Read($IV, 0, $LIV) | Out-Null $AESProvider.IV = $IV } catch { $FileStreamReader.Close() $FileStreamWriter.Close() Remove-Item $DestinationFile -Force $FailedToDecryptFiles += $File Write-Error "Unable to read IV from $($File.FullName), verify this file was made using the included EncryptFile function." Continue } Write-Verbose "Decrypting $($File.FullName) with an IV of $([System.Convert]::ToBase64String($AESProvider.IV))" #Decrypt try { $Transform = $AESProvider.CreateDecryptor() [Int]$Count = 0 [Int]$BlockSizeBytes = $AESProvider.BlockSize / 8 [Byte[]]$Data = New-Object Byte[] $BlockSizeBytes $CryptoStream = New-Object System.Security.Cryptography.CryptoStream($FileStreamWriter, $Transform, [System.Security.Cryptography.CryptoStreamMode]::Write) Do { $Count = $FileStreamReader.Read($Data, 0, $BlockSizeBytes) $CryptoStream.Write($Data, 0, $Count) } While ($Count -gt 0) $CryptoStream.FlushFinalBlock() $CryptoStream.Close() $FileStreamWriter.Close() $FileStreamReader.Close() #Delete encrypted file Remove-Item $File.FullName Write-Verbose "Successfully decrypted $($File.FullName)" $DecryptedFiles += $DestinationFile } catch { Write-Error "Failed to decrypt $($File.FullName)." $CryptoStream.Close() $FileStreamWriter.Close() $FileStreamReader.Close() Remove-Item $DestinationFile $FailedToDecryptFiles += $File } } } $Result = New-Object -TypeName PSObject $Result | Add-Member -MemberType NoteProperty -Name Computer -Value $env:COMPUTERNAME $Result | Add-Member -MemberType NoteProperty -Name AESKey -Value $Key $Result | Add-Member -MemberType NoteProperty -Name FilesDecryptedwAESKey -Value $DecryptedFiles $Result | Add-Member -MemberType NoteProperty -Name FilesFailedToDecrypt -Value $FailedToDecryptFiles return $Result } |