<?php
function encryptData($data, $key) {
    $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc'));
    $encrypted = openssl_encrypt($data, 'aes-256-cbc', $key, 0, $iv);
    return base64_encode($encrypted . '::' . $iv);
}

function decryptData($data, $key) {
    list($encryptedData, $iv) = explode('::', base64_decode($data), 2);
    return openssl_decrypt($encryptedData, 'aes-256-cbc', $key, 0, $iv);
}

$key = 'bu_gizli_bir_anahtar';
$encryptedData = encryptData($_POST['data'], $key);

echo '<a href="site.com?data=' . urlencode($encryptedData) . '">Gizli Veri</a>';
$decryptedData = decryptData($_GET['data'], $key);
echo 'Çözülmüş Veri: ' . $decryptedData;
?>