Encrypting the session section in web.config file.

Question

1. After encrypting the session section, change it in plain text and also change the timeout, So I verified it is taking the plain text timeout, but this wrong it should take time of encrypted part as what will be benefit of encrypting session.
2. Anybody can change the session, and increase the timeout, so please give the solution for it.
3. How to secure session timeout in web.config file