Perl

Decrypt File in Chunks using 256-bit AES

See more Encryption Examples

Shows how to decrypt a file chunk-by-chunk using FirstChunk/LastChunk properties and accumulate the results in memory with a Chilkat BinData object. Perl

use chilkat();

$success = 0;

# 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 = chilkat::CkCrypt2->new();

$crypt->put_CryptAlgorithm("aes");
$crypt->put_CipherMode("cbc");
$crypt->put_KeyLength(256);

$crypt->SetEncodedKey("000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F","hex");
$crypt->SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex");

$fileToDecrypt = "c:/temp/qa_output/hamlet.enc";
$facIn = chilkat::CkFileAccess->new();
$success = $facIn->OpenForRead($fileToDecrypt);
if ($success != 1) {
    print "Failed to open file to be decrytped." . "\r\n";
    exit;
}

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

$crypt->put_FirstChunk(1);
$crypt->put_LastChunk(0);

$bd = chilkat::CkBinData->new();
$bdDecrypted = chilkat::CkBinData->new();

$i = 0;
while ($i < $numChunks) {
    $i = $i + 1;
    if ($i == $numChunks) {
        $crypt->put_LastChunk(1);
    }

    # 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->put_FirstChunk(0);
}

# Make sure both FirstChunk and LastChunk are restored to 1 after
# encrypting or decrypting in chunks.  Otherwise subsequent encryptions/decryptions
# will produce unexpected results.
$crypt->put_FirstChunk(1);
$crypt->put_LastChunk(1);

$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");