Question

Computer Security

Bell-LaPadula Model

Given the access rights as follows:

Nada can read and write to file A, can append to file B, and can write to file C. Maha can read file A, can write to file B, and cannot access file C. Write the access control matrix M that specifies the described set of access rights for subjects Nada and Maha to objects file A, file B and file C.

Then the subject’s security levels are LNada= Confidential and LMaha = Secret, and the object’s security levels are Lfile A= Unclassified, Lfile B = Secret, Lfile C= Top Secret (Top Secret > Secret > Confidential > Unclassified).

1. a) Draw a Bell-LaPadula model which visualizes the access rights defined in access control matrix M.

2. b) Using the Bell-LaPadula model, which of the following actions are allowed?Explainand justify your answer.

   1. Nada reads file A

   2. Nada reads file B

   3. Maha appends to file A

   4. Maha appends to file C

Answer 1

The access matrix is shown in the below attached image.

a) Bell-LaPadula model is drawn and attached in the below image.

b) Nada reads file A is possible.According to Bell-LaPadula model subject can get read access to objects whose security level is below the subject clearance level.Here Naha having a level of confidential and object A having a level of unclassified. Since confidential>unclassified, Naha can read file A.

Nada Reads File B: Nada's security level is confidential.It is lesser than secret (level of object B)To read the object it must be below security level than subject.So this operation not possible.

Maha appends to file A: According to Bell-LaPadula model subject can get append access to objects whose security level is higher than the subject clearance level.Here subject Maha is having a greater security level secret than FilA(unclassified).So this operation is not possible.

Maha appends to file C: This is possibile since the security level of File C(Top secret) is greater than that of subject Maha(secret)