Question

I’m trying to create a kind of file generator in Php. Basically, it get a default file, read data, decrypt the data (Encrypted in AES), encrypt the data with the user password and paste all these bytes into a new file with the client name.

This sould be easy but I got some problems. Here is my current code:

// Load the original raw file
$data = file_get_contents('default.bin');
if (!$data) exit();

// Decrypt the raw data with the default key
$data = AESDecrypt($data, 'default_16_b_key');

// Encrypt the raw data with the user key
$data = AESEncrypt(pad($data, 16), $user_key);

$fileName = sprintf('client_%s.bin', $client_name);
file_put_contents($fileName, $data);

Here are the functions I’m using:

function AESEncrypt($data, $key)
{
    return mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $data, MCRYPT_MODE_ECB);
}

function AESDecrypt($data, $key)
{
    return mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $data, MCRYPT_MODE_ECB);
}

function pad($data, $blocksize)
{ 
    $pad = $blocksize - (strlen($data) % $blocksize); 
    return $data . str_repeat(chr($pad), $pad); 
}

The AES functions work well as I can decrypt and encrypt a simple string. The pad function seems to do its job to.

The problem is when I try to execute the generated file (which is a jar file after being renamed), I got this message “Unexpected file end” and nothing into my jar file except a blank file (0 byte).

Could you help me to solve this?

Answer 1

Finally, I solved it without using the first decryption.
It’s possible to encrypt the raw data using the following code:

$data = AESEncrypt(pad($data, 16), $user_key);

You can put that line in an infinite loop (no really infinite btw) and this will still work. Then you can decrypt it in the language of your choice.

Thanks.