Caesar Hack

CaesarHack.php

<?php
/**
 * Caesar Hack
 */
$message = 'GUVFVFZLFRPERGZRFFNTR';
$letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

for ($j = 0; $j < strlen($letters); $j++) {
    $trans = '';
    for ($i = 0; $i < strlen($message); $i++) {
        $num = strpos($letters, $message[$i]);
        $num -= $j;
        
        if ($num < 0) {
            $num += strlen($letters);
        }
        $trans .= $letters[$num];        
    }
    echo "{$j} {$trans}" . PHP_EOL;
}