Encrypt url paramters in ruby, decrypt in PHP. Logic issue

Question

Encrypted: http://example.com/3ISGSfzIiaAU+h2TwF0pNoKDKRenjKfRhehMMN3+OJw=

Decrypted: http://example.com/opens.php?subid=66

This url is a pixel which is fired when someone opens an Email.

Everything is working fine, when I load the pixel decrypted. I don't get the logic how to decrypt the link in the email so it can load.

My question: Where should I use the decryption function in order to load the url?

Ruby encryption:

 require 'openssl'
 require 'base64'

 class String
  def self.encrypt(plain_text)
    cipher = OpenSSL::Cipher.new('aes-256-cbc')
    cipher.encrypt
    iv = 'akjgkdladjgkadsw'
    iv64 = [iv].pack("m").strip
    key = 'o1diqwkadkfjg018jgkdja9194025123'
    key64 = [key].pack("m").strip

    cipher = OpenSSL::Cipher.new('aes-256-cbc')
    cipher.encrypt
    cipher.key = Base64.decode64(key64)
    cipher.iv = Base64.decode64(iv64)
    encrypted_data = cipher.update(plain_text)
    encrypted_data << cipher.final
    crypt64 = [encrypted_data].pack("m").strip
  end
end

Basic decryption.php:

<?php
class String {
    function decrypt($string) {
        $ruby_crypt = $string;
        $encrypted_data = base64_decode($ruby_crypt);
        $key = base64_decode("bzFkaXF3a2Fka2ZqZzAxOGpna2RqYTkxOTQwMjUxMjM=");
        $iv = base64_decode("YWtqZ2tkbGFkamdrYWRzdw==");
        $result = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $encrypted_data, MCRYPT_MODE_CBC, $iv);
        $unencrypt = rtrim($result, "\x00..\x1F");
        //print "\nUnencrypted token:\n'$unencrypt'\n";
    }
}
?>

Grab the parameter and make the DB entries (opens.php):

<?php
require_once("./db_connection.php");
include("./decryption.php");

// Create connection
$conn = new mysqli($servername, $username, $password, $db);

// Check connection
if($conn->connect_error) {
 exit('Error connecting to database');
}
$conn->set_charset("utf8");     
// echo "Connected successfully";

$id = intval($_REQUEST['subid']);

$stmt = $conn->prepare("UPDATE rcpt SET has_opens = has_opens + 1 WHERE id = ? ");
$stmt->bind_param('i', $id);
$stmt->execute();
$stmt->close();

header('Content-Type: image/gif');
$img = imagecreatefromgif("px.gif");
imagegif($img);
imagedestroy($img);

mysqli_close($conn);
?>