| Bell-lapadula Model |
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to formalize the U.S. Department Of Defense (DoD) Multilevel Security (MLS) policy. 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-LaPadula model is an example of a model where there's no clear Distinction Of Protection And Security . Landwehr 81, pp. 8, 11 FEATURES The Bell-LaPadula model focuses on data Confidentiality and access to Classified Information , in contrast to the Biba Integrity Model which describes rules for the protection of Data Integrity . In this formal model, the entities in an Information System are divided into subjects and objects. The notion of a " Secure State " is defined, and it is proven that each state transition preserves security by moving from secure state to secure state, thereby Inductively proving that the system satisfies the security objectives of the model. The Bell-LaPadula model is built on the concept of a State Machine with a set of allowable states in a system. The transition from one state to another state is defined by Transition Functions . A system state is defined to be "secure" if the only permitted access modes of subjects to objects are in accordance with a Security Policy . To determine whether a specific access mode is allowed, the clearance of a subject is compared to the classification of the object (more precisely, to the combination of classification and set of compartments, making up the ''security level'') to determine if the subject is authorized for the specific access mode. The clearance/classification scheme is expressed in terms of a Lattice . The model defines two Mandatory Access Control (MAC) rules and one Discretionary Access Control (DAC) rule with three security properties: # ''The Simple Security Property'' states that a subject at a given security level may not read an object at a higher security level (no read-up).
# ''The Discretionary Security Property'' uses an Access Matrix to specify the discretionary access control.
This security model is directed toward access control and is characterized by the phrase: no read up, no write down. Compare the Biba Model , the Clark-Wilson Model and the Chinese Wall . With Bell-LaPadula, users can create content only at or above their own security level (''Secret'' researchers can create ''Secret'' or ''Top-Secret'' files but may not create ''Public'' files): '''no write-down.''' Conversely, users can '''view content only at or below''' their own security level (''Secret'' researchers can view ''Public'' or ''Secret'' files, but may not view ''Top-Secret'' files): '''no read-up.''' The Bell-LaPadula model explicitly defined its scope. It did not treat the following extensively:
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