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Security Engineering


1)      According to Bell-Lapadula model, if there is reading down restrictions, user who is accessing the restricted area, can only read places where access level is lower than the access granted to him. Therefore user wouldn’t be able to reach high access level parts of the restricted area.  (‘Manocha H’, ‘1999’)

For Bell-Lapadula writing up makes the user access objects where access level higher than his current access. That would prevent them passing information to lower level accesses than its current level.

For Biba model, there is no read down, a subject that given an access to a level must not read an object at a lower integrity. In same manner, there is no write up, a subject must not write at any object that is higher level than current integrity. (Commondork, 2010)


2)      Checking if Windows 7 is comply Clark Wilson method was quite easy as Microsoft already announced that, Windows 7’s integrity mechanism is not designed to protect high data support for commercial or military requirements as Clark Wilson method talking about. There is no Constrained or Unconstrained data items in Windows implementation of integrity nor transformation procedures are certified. Meanwhile Microsoft recommends that these methods are useful for application designers and they say that application designers should consider about using these.

As a long time Microsoft user, I can say that their security mechanism has changed in the time. Especially trying to implement Trust Computing to their operating systems, made them more paranoid about security. There are some default settings (which user can disable) asking administrator account’s permission even when user try to install a software or change settings on the computer. These settings are more or less Biba style, rather than Clark Wilson.


‘Bell-La Padula, Biba and Clark-Wilson Security Models’ (2010), ‘Common Dork’, [Online] available from viewed 4 July 2012

‘Manocha H’ (1999), ‘Protection: Bell-Lapadula Model’, ‘Virginia Tech’, [Online] available from viewed 4 July 2012

‘Windows Integrity Mechanism Design’ (nd), ‘MSDN’, [Online], Available from viewed 4 July 2012


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