1. CSC 386 – Computer Security Scott Heggen

2. Agenda Bell-LaPadula Model of Computer Security

3. Bell-LaPadula (BLP) Goals: State machine model developed in the 1970s for the analysis of MLS operating systems. Subjects and objects labeled with security levels that form a partial ordering. The policy: No information flow from ‘high’ security levels down to ‘low’ security level (confidentiality). Only considers information flows that occur when a subject observes or alters an object. Access permissions defined through an access control matrix and security levels.

4. State Machine OffOn

5. BLP PublicSecret Top Secret Her Majesty’s Eyes Only Read? No Read-up!

6. BLP PublicSecret Top Secret Her Majesty’s Eyes Only Read? Read-down okay!

7. BLP PublicSecret Top Secret Her Majesty’s Eyes Only Write? No write-down!

8. BLP PublicSecret Top Secret Her Majesty’s Eyes Only Write? Write-up okay!

9. BLP Reading: Okay from high-to-low level Forbidden from low-to-high level Writing: Okay from low-to-high level Forbidden from high-to-low level No Read-up ss-property No Write-down ★ -property

10. BLP Other cases Should all “Top Secret” subjects be able to see all “Top Secret” objects? The discretionary security property (ds-property) handles individual cases

11. Implementing BLP Scenario: Create four people: Larry, Curly, Moe, and Shemp Give each person a security level: Moe - Her Majesty’s Eyes Only Larry – Top Secret Curly – Secret Shemp – Public Modify the blpmain.py program so that it: Allows any person to create a file. The file should include the creator’s security level (so you can check it later). Allow each person to READ files at or below their security level Allow each person to WRITE (append) to a file at or above their security level