What are some other levels of protection that users

In Chapter 4:
Q9. What are some other levels of protection that users might want to apply to code or data, in addition
to the common read, write, and execute permission?

Q23.Design a protocol by which two mutually suspicious parties can authenticate each other. Your protocol should be usable the first time these parties try to authenticate each other.

Q.Explain how relocation protects the Memory.