• Information security is an important issue in modern world.
• For this purpose many security models have been developed to enforce it. One of the most popular models is the Bell-LaPadula model.
• All Information is not of the same priority level as another. Information’s like military confidential are matters of grave national importance and needs to be highly secured.
• The different subjects (people or programs) have varying rights of access to objects (information)
• E.g. In military, the documents can be categorized as Unclassified, ,confidential, secret, etc. Now different subjects (officers) have different access rights to this information based on the classification.
• Such security enforcement is referred to as multilevel security. Bell-LaPadula is a form of multilevel security.
• The general statement of the requirement for multilevel security is that a subject (e.g military-field marshal –the highest rank) at a high level may not convey information to a subject at a lower(e.g. subedar) or incompatible level unless that flow accurately reflects the will of an authorized user
• This can be implemented using the Bell LaPadula Model, in which a multilevel secure system must enforce:
  • No read up (Simple Security Property):
    • a subject can only read/write an object if the current security level of the subject dominates (>=) the classification of the object
    • In simpler terms, a subject can only read an object of less or equal security level.
  • No write down: (*-property)
    • a subject can only append/write to an object if the current security level of the subject is dominated by (<=) the classification of the object
    • In simpler terms, a subject can only write into an object of greater or equal security level
  • Strong Star
  • The strong star property states that a subject that has read and write capabilities can only perform those at the same security level , nothing higher or nothing lower.
  • A subject to read and write to an object , clearance(security level of document) and classification(security level of officer) must be equal

Bell-LaPadula model has two major limitations:

• It provides confidentiality only. (no integrity, authentication ,etc.)
• It provides no method for management of classifications:
  • It assumes all data are assigned with a classification
  • It assumes that the data classification will never change.