基于cesar密码的php替换编码算法

<?php
function caesarCipher($text, $shift, $encrypt = true) {
    $result = '';
    $alphabet = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $length = strlen($alphabet);

    for ($i = 0; $i < strlen($text); $i++) {
        $char = $text[$i];
        $position = strpos($alphabet, $char);

        if ($position === false) {
            $result .= $char;
        } else {
            if ($encrypt) {
                $newPosition = ($position + $shift) % $length;
            } else {
                $newPosition = ($position - $shift + $length) % $length;
            }
            $result .= $alphabet[$newPosition];
        }
    }

    return $result;
}

// 示例使用
$plaintext = "Hello, World!";
$shift = 3;

$encrypted = caesarCipher($plaintext, $shift, true);
echo "Encrypted: " . $encrypted . "\n";

$decrypted = caesarCipher($encrypted, $shift, false);
echo "Decrypted: " . $decrypted . "\n";
?>