openssl_encrypt_decrypt.php

function encrypt_decrypt($action, $string) {
   $output = false;
   $encrypt_method = "AES-256-CBC";
   $secret_key = 'This is my secret key';
   $secret_iv = 'This is my secret iv';
   // hash
   $key = hash('sha256', $secret_key);

   // iv - encrypt method AES-256-CBC expects 16 bytes - else you will get a warning
   $iv = substr(hash('sha256', $secret_iv), 0, 16);
   if ( $action == 'encrypt' ) {
       $output = openssl_encrypt($string, $encrypt_method, $key, 0, $iv);
       $output = base64_encode($output);
   } else if( $action == 'decrypt' ) {
       $output = openssl_decrypt(base64_decode($string), $encrypt_method, $key, 0, $iv);
   }
   return $output;
}