<?php $codebook = array( 'A' => 'a', 'sun' => 'frog', 'rises' => 'jumps' ); $message = 'The sun rises.'; $encoded_message = str_ireplace(array_keys($codebook), array_values($codebook), $message); $decoded_message = str_ireplace(array_values($codebook), array_keys($codebook), $encoded_message); ?>