Given security levels (Top Secret, Secret, Classified, Unclassified) and that To

Question

Given security levels (Top Secret, Secret, Classified, Unclassified) and that Top

Secret > Secret > Classified > Unclassified that can be assigned to subjects who need

to be controlled access to objects that may contain data of categories {A, B, C}. User

can be given READ, WRITE, READ+WRITE, NONE type of access to the objects.

Assuming that the system implements the Discretionary or Manditory-Policy, as defined

by the Bell-La Padula model, what type access will granted for the cases listed below:

a) Alice is cleared for (Top Secret, {A, C} ) and wants to access a document

classified as (Secret, {B, C})

b) Bob is cleared for (Secret, {A}) wants to access (Secret, {B})

c) Claire is cleared for (Top Secret, {A, C}} and wants to access a document

classified as ( Confidential, {A, C})

d) Dave is cleared for (Secret, {A, B}) and wants to access a document classified as

(Top Secret, {A} )

e) Elsa has UNCLASSIFIED designation and wants access a document classified as

(Confidential, {A} )

Explanation / Answer

Solution :

a. LAlice = TOPSECRET SECRET = Ldoc, so Alice cannot write the document. Alice cannot read the document either, because Cdoc = { B, C } { A, C } = CAlice.

b. LBob = SECRET SECRET = Ldoc, but Cdoc = { B } { A } = CBob so Bob cannot read the document, and CBob = { A } { B } = Cdoc, so Bob cannot write the document.  

c. As LClaire = TOPSECRET CONFIDENTIAL = Ldoc and Cdoc = { A, C } { A, C } = CClaire, Claire can read the document. But the first inequality means Claire cannot write the document.

d. LDave = SECRET TOPSECRET = Ldoc, and Cdoc = { A } { A, B } = CDave, so Dave can read the document. As LDave > Ldoc, however, Dave cannot write the document.

e. As CElsa = { A } = Cdoc and Ldoc = CONFIDENTIAL UNCLASSIFIED = LElsa, Elsa can write the document. However, because Ldoc LElsa, she cannot read the document.

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