PHP sending encrypted data via the URL

Question

I'm trying to send encrypted data over the url to another site (using file_get_contents("anotherUrl.php?hash=$encryptedString"). The problem is, sometimes, the encryption contains some special characters, like +, and this causes the decryption to fail.

Here are my encryption / decryption methods:

public function encrypt($string, $key)
{
    return base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, md5($key), $string, MCRYPT_MODE_CBC, md5(md5($key))));
}

public function decrypt($encrypted, $key)
{
    return rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, md5($key), base64_decode($encrypted), MCRYPT_MODE_CBC, md5(md5($key))), "\0");
}

Here's an example encrypted string which contains a +, and I'm guessing that this causes the decryption to fail.

oWCrVPaS+5GbxcQFc0fulUk/zRAkDD60av4zlPiWskE=

Any ideas how I should solve this? I've tried to do urlencode() and urldecode() on the hash, however that also seems to cause the encryption to break. Is there a way to change the encryption algorithm to get it to only return url safe characters?

Answer 1

In order to solve this problem I now use the following (after 3 hours of pain), and it works great.

Feel free to copy and paste

function encrypt($pure_string) {
    $dirty = array("+", "/", "=");
    $clean = array("_PLUS_", "_SLASH_", "_EQUALS_");
    $iv_size = mcrypt_get_iv_size(MCRYPT_BLOWFISH, MCRYPT_MODE_ECB);
    $_SESSION['iv'] = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $encrypted_string = mcrypt_encrypt(MCRYPT_BLOWFISH, $_SESSION['encryption-key'], utf8_encode($pure_string), MCRYPT_MODE_ECB, $_SESSION['iv']);
    $encrypted_string = base64_encode($encrypted_string);
    return str_replace($dirty, $clean, $encrypted_string);
}

function decrypt($encrypted_string) { 
    $dirty = array("+", "/", "=");
    $clean = array("_PLUS_", "_SLASH_", "_EQUALS_");

    $string = base64_decode(str_replace($clean, $dirty, $encrypted_string));

    $decrypted_string = mcrypt_decrypt(MCRYPT_BLOWFISH, $_SESSION['encryption-key'],$string, MCRYPT_MODE_ECB, $_SESSION['iv']);
    return $decrypted_string;
}