The Bell-La Padula Model is a state machine model used for enforcing access control in government and military applications. The model is a formal state transition model of computer security policy that describes a set of access control rules which use security labels on objects and clearances for subjects. Security labels range from the most sensitive (e.g.,"Top Secret"), down to the least sensitive (e.g., "Unclassified" or "Public").

The Bell-La Padula model focuses on data confidentiality and controlled access to classified information, in contrast to the Biba Integrity Model which describes rules for the protection of data integrity. Answer: B is incorrect. The Biba model is a formal state transition system of computer security policy that describes a set of access control rules designed to ensure data integrity. Data and subjects are grouped into ordered levels of integrity. The model is designed so that subjects may not corrupt data in a level ranked higher than the subject, or be corrupted by data from a lower level than the subject. Answer: A is incorrect. The Clark-Wilson model provides a foundation for specifying and analyzing an integrity policy for a computing system. The model is primarily concerned with formalizing the notion of information integrity. Information integrity is maintained by preventing corruption of data items in a system due to either error or malicious intent. The model's enforcement and certification rules define data items and processes that provide the basis for an integrity policy. The core of the model is based on the notion of a transaction. Answer: C is incorrect. The take-grant protection model is a formal model used in the field of computer security to establish or disprove the safety of a given computer system that follows specific rules. It shows that for specific systems the question of safety is decidable in linear time, which is in general undecidable. The model represents a system as directed graph, where vertices are either subjects or objects. The edges between them are labeled and the label indicates the rights that the source of the edge has over the destination. Two rights occur in every instance of the model: take and grant. They play a special role in the graph rewriting rules describing admissible changes of the graph.

The tools used in DRM to define the level of robustness are as follows: 1.Widely available tools: These tools are easy to use and are available to everyone. For example, screw-drivers and file editors. 2.Specialized tools: These tools require skill and are available at reasonable prices. For example, debuggers, decompilers, and memory scanners. 3.Professional tools: These tools are expensive, require skill, and are not easily available. For example, logic analyzers, circuit emulators, and chip disassembly systems.

Top Secret information is the highest level of classification of material on a national level. Such material would cause "exceptionally grave damage" to national security if publicly available. Answer: A is incorrect. Secret information is that, if disclosed to unauthorized parties, could be expected to cause serious damage to the national security, but it is not the best answer for the above question. Answer: C is incorrect. Such material would cause "damage" or be "prejudicial" to national security if publicly available. Answer: B is incorrect. Unclassified information, technically, is not a classification level, but is used for government documents that do not have a classification listed above. Such documents can sometimes be viewed by those without security clearance.