Question

I am trying to come up with a way to have PHP encrypt a file. I used to just use a PHP system call to run a script that encoded the file:

#!/bin/sh
/usr/bin/openssl aes-256-cbc -a -salt -k $1 -in $2

Argument 1 was the password to use and argument 2 is the data. I then use a second script on a computer to de-crypt the file.

#!/bin/sh
/usr/bin/openssl aes-256-cbc -a -d -salt -k $1 -in $2

This method of encrypting will not work on a production host as the PHP system call is disabled. I also would prefer not the change the decode function if at all possible.

Is there a way to replicate the above encrypt function using only PHP?

Answer 1

As stated above in the comments padding is necessary to make this work. The function below will make a file that can be decrypted on the command line like this:

openssl enc -d -aes-256-cbc -a -salt -in test.txt

The test.txt file is created from the output of the ssl_encrypt function below.

function ssl_encrypt($pass, $data)
{
    // Set a random salt
    $salt = substr(md5(mt_rand(), true), 8);

    $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    $pad = $block - (strlen($data) % $block);

    $data = $data . str_repeat(chr($pad), $pad);

    // Setup encryption parameters
    $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, "", MCRYPT_MODE_CBC, "");


    $key_len =  mcrypt_enc_get_key_size($td);
    $iv_len =  mcrypt_enc_get_iv_size($td);

    $total_len = $key_len + $iv_len;
    $salted = '';
    $dx = '';
    // Salt the key and iv
    while (strlen($salted) < $total_len)
    {
        $dx = md5($dx.$pass.$salt, true);
        $salted .= $dx;
    }
    $key = substr($salted,0,$key_len);
    $iv = substr($salted,$key_len,$iv_len);


    mcrypt_generic_init($td, $key, $iv);
    $encrypted_data = mcrypt_generic($td, $data);
    mcrypt_generic_deinit($td);
    mcrypt_module_close($td);


    return chunk_split(base64_encode('Salted__' . $salt . $encrypted_data),32,"\r\n");
}

Example Usage:

$plainText = "Secret Message";
$password = "SecretPassword";
$test = ssl_encrypt($password, $plainText);
$file = fopen('test.txt', 'wb');
// Write the Base64 encrypted output to a file.
fwrite($file, $test);
fclose($file);
// Show the output on the screen
echo $test;

References: http://juan.boxfi.com/2010/03/16/write-openssl-files-in-php/