Song Decrypt

<?php
$re = '/^[A-Z][a-z]*\s?[a-z]*:[A-Z\s]*$/m';
$input = readline();
$match = "";
while (true) {
    if ($input=="end"){
        break;
    }
    if (preg_match($re, $input, $match)) {
        $tokens = explode(":", $input);
        $artist = $tokens[0];
        $song = $tokens[1];
        $decrypt = "";
        $key = strlen($artist);
        for ($i = 0; $i < strlen($input); $i++) {
            $current = $input[$i];
            if ($current == " ") {
                $decrypt .= " ";
                continue;

            }else if($current==":"){
                $decrypt .= "@";
                continue;
            }
            else if (ord($current) + $key > 90 && ctype_upper($current)) {
                $decrypt .= chr(65 + $key);
            } else if (ord($current) + $key > 122 && ctype_lower($current)) {
                $decrypt .= chr(97 + $key);
            } else {
                $decrypt .= chr(ord($current) + $key);
            }

        }
        echo "Successful encryption: $decrypt". PHP_EOL;


    } else {
        echo "Invalid input!";
    }
    $input = readline();

}