Data Protection and Security

V

Access Control

V.IV

Multilevel Security

The Lattice of Security Levels

Security levels, attributes used to label subjects and objects, are the basis for expressing security policies. Note that, we can only express a limited set of security policies if we insist on a linear ordering (seen above) of security levels.

Partial ordering meets better our security requirements because we do not require every two levels to be comparable (either below or above to the other one). The mathematical structure used to express multilevel security policies is called a lattice. Informally speaking, a lattice is a set of levels with partial ordering where there are one absolute minimum and one absolute maximum elements.

Some multilevel security products find a new lease on life as platforms for firewalls and web servers. Below is a lattice example for a firewall. This lattice could be used to achieve a strict separation between the inside and outside of a network.