The Bell-LaPadula model is used to enforce access control within the government and military. It was developed by David Elliott Bell and Leonard J. LaPadula, hence the funny name. The Bell-LaPadula model focuses on confidentiality. While the formal model may not be applicable for most uses, the terminology and concepts are still important to passing the CISSP exam. As you review the model, think of the military uses of clearance levels, it will make understanding easier.

Unclassified < Confidential < Secret < Top Secret

In a nutshell, the Bell-LaPadula model prevents a user with a Secret clearance from viewing a Top Secret document (no read up). It also prevents a user from putting Top Secret information within a Secret document (no write down). In this model, the entities are divided into subjects and objects. Think of subjects as users and objects as computers or documents. To determine whether access is allowed, the clearance of a subject is compared to the classification of the object and a determination is made as to whether the subject is authorized for the specific access mode.

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