Example to encrypt a file (even big) using Zend\Filter\Encrypt of ZF2 with a simple block schema (low memory consumption).

encrypt_file.php

<?php
// include the ZF2 library
use Zend\Filter\Encrypt;

if (!isset($argv[1]) or !isset($argv[2])) {
    die("Usage: " . basename(__FILE__) . " <file_to_encrypt> <encryption_key>\n");
}

if (!file_exists($argv[1])) {
    die("The file {$argv[1]} specified doesn't exist\n");
}

$fileIn  = $argv[1];
$fileOut = $fileIn . '.enc';
$buffer  = 1048576; // 1 MB (increase if needed)

$filter = new Zend\Filter\Encrypt(array('adapter' => 'BlockCipher'));
$filter->setKey($argv[2]);

$read  = @fopen($fileIn, "r");
$write = @fopen($fileOut, "w");

while (!feof($read)) {
    $data = fread($read, $buffer);
    fwrite($write, $filter->filter($data));
}

fclose($write);
fclose($read);