I have a PHP script that does basic encryption of a string through the method below:

<?php
$key = 'secretkey';
$string = $_GET['str'];

if ($_GET['method'] == "decrypt")
{
    $output = rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, md5($key), base64_decode($string), MCRYPT_MODE_CBC, md5(md5($key))), "\0");
}

if ($_GET['method'] == "encrypt")
{
    $output= base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, md5($key), $string, MCRYPT_MODE_CBC, md5(md5($key))));
}

echo $output;
?>

An example of a URL to encrypt a string would look like this:

Encrypt.php?method=encrypt&str=the quick fox

Which would return this as the encrypted string:

LCuT/ieVa6cl3/4VtzE+jd9QPT3kvHYYJFqG6tY3P0Q=

Now to decrypt the string all you have to do is change the "method" query to "decrypt", like so:

Encrypt.php?method=decrypt&str=LCuT/ieVa6cl3/4VtzE+jd9QPT3kvHYYJFqG6tY3P0Q=

The only problem is that when that encrypted string is decrypted it returns this:

¬ƒ§rYV}̳5Äš·nßì(ñïX8Þ;b

I have narrowed down the problem to the plus sign that is in the encrypted string. PHP's GET method seems to translate a plus sign into a blank space. I have searched this bug and found out that it has already been filed here. I have tried different methods listed on that page and others with no success. The closest I got is by using this:

$fixedstring = str_replace(" ", "+", $string);

and then using $fixedstring in the encryption methods, the problem is, upon decryption, all blank spaces are converted to plus signs. Any ideas?