PHP

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 PHP

<?php

use Chilkat2\BinData;
use Chilkat2\Crypt2;
use Chilkat2\FileAccess;

// 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 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 FileAccess();
try {
    $facIn->OpenForRead($fileToDecrypt);
} catch (\Chilkat2\Exception $e) {
    echo "Failed to open file to be decrytped.\n";
    exit;
}

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

$crypt->FirstChunk = true;
$crypt->LastChunk = false;

$bd = new BinData();
$bdDecrypted = new BinData();

$i = 0;
while ($i < $numChunks) {
    $i = $i + 1;
    if ($i == $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');