(PowerShell) Decrypt File in Chunks using 256-bit AES

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Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$success = $false

# This example assumes the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

# This example decrypts the file previously encrypted in this example:
# Encrypt File in Chunks using AES CBC

$crypt = New-Object Chilkat.Crypt2

$crypt.CryptAlgorithm = "aes"
$crypt.CipherMode = "cbc"
$crypt.KeyLength = 256

$crypt.SetEncodedKey("000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F","hex")
$crypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex")

$fileToDecrypt = "c:/temp/qa_output/hamlet.enc"
$facIn = New-Object Chilkat.FileAccess
$success = $facIn.OpenForRead($fileToDecrypt)
if ($success -ne $true) {
    $("Failed to open file to be decrytped.")
    exit
}

# Let's decrypt in 32000 byte chunks.
$chunkSize = 32000
$numChunks = $facIn.GetNumBlocks($chunkSize)

$crypt.FirstChunk = $true
$crypt.LastChunk = $false

$bd = New-Object Chilkat.BinData
$bdDecrypted = New-Object Chilkat.BinData

$i = 0
while ($i -lt $numChunks) {
    $i = $i + 1
    if ($i -eq $numChunks) {
        $crypt.LastChunk = $true
    }

    # Read the next chunk from the file.
    # The last chunk will be whatever amount remains in the file..
    $bd.Clear()
    $facIn.FileReadBd($chunkSize,$bd)

    # Decrypt this chunk.
    $crypt.DecryptBd($bd)
    # Accumulate the decrypted chunks.
    $bdDecrypted.AppendBd($bd)

    $crypt.FirstChunk = $false
}

# Make sure both FirstChunk and LastChunk are restored to $true after
# encrypting or decrypting in chunks.  Otherwise subsequent encryptions/decryptions
# will produce unexpected results.
$crypt.FirstChunk = $true
$crypt.LastChunk = $true

$facIn.FileClose()

# The fully decrypted file is contained in bdDecrypted.
# You can save to a file if desired, or use the decrypted data in your application directly from bdDecrypted.
$bdDecrypted.WriteFile("c:/temp/qa_output/hamlet_decrypted.xml")