Encrypt using dynamic key

Using Dynamic Key
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If specify the $key as ENCRYPT_DYNAMIC_KEY then it will use dynamic key based
on below variables.

// Developer needs to assign any userid to this session variable
$_SESSION['ENCRYPT']['uid']

// Developer needs to assign guid of that user used above to this session
// variable.
$_SESSION['ENCRYPT']['guid']

// If either of the above session variables are not available then fetch info
// from the current user.
global $user
$user->uid
$user->uid