PHP AES Encryption PKCS5Padding

Question

I am not a PHP encoder, so I need a little help with PHP AES encryption.

I write code where I encrypt image files in PHP and then decrypt them in Java (Android). Everything works fine when I encrypt / decrypt PNG files, but when I try to do the same with JPG, Java decryption throws an exception:

WARN/System.err(345): java.io.IOException: data not block size aligned 

Based on an Internet search, it seems that this is due to the fact that I am filling out the content incorrectly.

How can I do it right?

Here is the PHP code for encryption:

 <?php $secret_key = "01234567890abcde"; $iv = "fedcba9876543210"; $infile = "5.png"; $outfile = "5_encrypted.png"; $crypttext = file_get_contents($infile); $plaintext = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $secret_key, $crypttext, MCRYPT_MODE_CBC, $iv); header('Content-Type: application/octet-stream'); header('Content-Length: ' . strlen($plaintext)); header('Content-Disposition: attachment; filename=' . ($outfile)); echo $plaintext; //file_put_contents($outfile,$plaintext); //save the file in the folder of server 

Answer 1

The following example for PKCS5Padding comes from comments in mcrypt docs .

 <?php function encrypt_something($input) { $size = mcrypt_get_block_size('des', 'ecb'); $input = pkcs5_pad($input, $size); $key = 'YOUR SECRET KEY HERE'; $td = mcrypt_module_open('des', '', 'ecb', ''); $iv = mcrypt_create_iv (mcrypt_enc_get_iv_size($td), MCRYPT_RAND); mcrypt_generic_init($td, $key, $iv); $data = mcrypt_generic($td, $input); mcrypt_generic_deinit($td); mcrypt_module_close($td); $data = base64_encode($data); return $data; } function pkcs5_pad ($text, $blocksize) { $pad = $blocksize - (strlen($text) % $blocksize); return $text . str_repeat(chr($pad), $pad); } function pkcs5_unpad($text) { $pad = ord($text{strlen($text)-1}); if ($pad > strlen($text)) return false; if (strspn($text, chr($pad), strlen($text) - $pad) != $pad) return false; return substr($text, 0, -1 * $pad); }