Homework 5 – Solution

CSCE 824, 2013

1. Access Control

While it is shown that lattice-based access control provides high assurance confidentiality in closed access control models (i.e., All permitted accesses are specified. If there is no positive permission can be derived for an access, it is denied). However, it is unclear how to use lattice-based access control in open systems (i.e., All denied accesses are specified. If there is no denial of an access can be derived, it is permitted.) Evaluate the applicability of the lattice-based access control model for open environment. Justify your answer.

2. Database Inference

Consider the following relation with element-level security granularity. (“U” stands for unclassified, “S” for secret security level, and “TC” represents the security level of the tuple, that is the lowest upper bound of the security levels of the cells in the tuple.) The primary key of the relation is the attribute Starship.

The view of this relation for a user with security clearance “unclassified” (U) is:

The non-authorized cell values are replaced with “Null.” Consider the case when a user with U clearance wants to update the record for Voyager. The user wants to update the objective of the Voyager to “Exploration” and the destination to “Talos.”

• Explain the problem(s) that would arise if such update is permitted.
• Explain the problem(s) that would arise if such update is denied.
• Suggest a secure solution how to handle the update that would not violate the key integrity constraint of the database.