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. Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

# 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

my $crypt = Chilkat2::Crypt2->new;

$crypt->CryptAlgorithm('aes');
$crypt->CipherMode('cbc');
$crypt->KeyLength(256);

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

my $fileToDecrypt = 'c:/temp/qa_output/hamlet.enc';
my $facIn = Chilkat2::FileAccess->new;
my $success = $facIn->OpenForRead($fileToDecrypt);
if (!$success) {
    print "Failed to open file to be decrytped.\n";
    exit;
}

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

$crypt->FirstChunk(1);
$crypt->LastChunk(0);

my $bd = Chilkat2::BinData->new;
my $bdDecrypted = Chilkat2::BinData->new;

my $i = 0;
while ($i < $numChunks) {
    $i = $i + 1;
    if ($i == $numChunks) {
        $crypt->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->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->FirstChunk(1);
$crypt->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');