Out of memory decrypting large files in PHP with phpseclib - php

Question

I'm trying to write a program that decrypts AES files on the fly with phpseclib.
Files are large, so I get an out of memory error if I use file_get_contents($f) or fread(filesize($f)) to read the input file.
For some reason, a loop like this is creating corrupted output files. WHY!? =(
For example, an input file of size 296,155,408 bytes comes out with 18,805,826 bytes. NOTE: It works if the entire file can be read in one iteration of the loop.
define('MY_BUFFER_SIZE', 128 * 1024);
$sessionKey = '....';
$filenameIn = $argv[1];
$fileIn = fopen($filenameIn, 'rb');
$filenameOut = dirname($argv[1]) . DIRECTORY_SEPARATOR . basename($argv[1], '.tar.gz') . '-decrypted.tar.gz';
$fileOut = fopen($filenameOut, 'wb');
// Setup cipher for continuous buffering and copy between files.
$aesCipher = new Crypt_AES(CRYPT_AES_MODE_CBC);
$aesCipher->setKey($sessionKey);
$aesCipher->setIV("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00");
$aesCipher->enableContinuousBuffer();
while (!feof($fileIn)) {
$packet = fread($fileIn, MY_BUFFER_SIZE); // #TODO: Streaming not working.
fwrite($fileOut, $aesCipher->decrypt($packet));
}
fclose($fileIn);
fclose($fileOut);

Answer 1

Thanks to #neubert!
What was required was adding:
$aesCipher->disablePadding()
This works:
// Setup cipher for continuous buffering and copy between files.
$aesCipher = new Crypt_AES(CRYPT_AES_MODE_CBC);
$aesCipher->setKey($sessionKey);
$aesCipher->setIV("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00");
$aesCipher->enableContinuousBuffer();
$aesCipher->disablePadding();
while (!feof($fileIn)) {
fwrite($fileOut, $aesCipher->decrypt(fread($fileIn, MY_BUFFER_SIZE)));
}