Computer security

4 approaches to security in computing, sometimes a combination of approaches is valid:

   1. Trust all the software to abide by a security policy but the software is not trustworthy (this is computer insecurity).
   2. Trust all the software to abide by a security policy and the software is validated as trustworthy (by tedious branch and path analysis for example).
   3. Trust no software but enforce a security policy with mechanisms that are not trustworthy (again this is computer insecurity).
   4. Trust no software but enforce a security policy with trustworthy hardware mechanisms.