14.3.1 Problem
You want to prevent data being viewable as plaintext. For
example, you don't want hidden form data to be revealed simply by someone
viewing the source code of a web page.
14.3.2 Solution
$personal_data = array('code' => 5123, 'blood_type' => 'O');
$info = base64_encode(serialize($personal_data));
print '<input type="hidden" name="info" value="'.$info.'">';
<input type="hidden" name="info"
value="YToyOntzOjQ6ImNvZGUiO2k6NTEyMztzOjEwOiJibG9vZF90eXBlIjtzOjE6Ik8iO30=">
$personal_data = unserialize(base64_decode($_REQUEST['info'])); get_transfusion($personal_data['blood_type']);