הצפנה דו-כיוונית ב-PHP

function encrypt($text, $key, $iv)
{
    return mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_CBC, $iv);
}

function decrypt($encrypted_text, $key, $iv)
{
    return mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $encrypted_text, MCRYPT_MODE_CBC, $iv);
}

$iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CBC));
$key = 'aoeuaoeuaoeuaoeuaoeaaaaaaaaeeesu'; // max 32 bytes

$enc = encrypt('Hello from phpguide.co.il', $key, $iv);
$dec = decrypt($enc, $key, $iv);

echo 'encrypted: ', $enc , '<br/>decrypted: ',$dec;

$value = '123456';
$salt = 'aoeuscxf0&*)(*)&(*^O)htjhsk';

setcookie('value', $value);
setcookie('validation', md5($value.$salt));
// ----------------------------------------
if( md5($_COOKIE['value'].$salt) != $_COOKIE['validation'] ) echo 'bad hacker!';