Homework #2

Due: April 24, 2026
Points: 100

Questions

1. (25 points) Expand the proof of Theorem 4–2 to show the statement, and the proof, of the induction.

2. (30 points) In class I said that the two properties of the hierarchy function (see Section 5.2.3) allow only trees and single nodes as organizations of objects. Prove this formally.

3. (15 points) Suppose a system used the same labels for integrity levels and categories as for subject levels and categories. Under what conditions could one subject read an object? Write to an object? Remember to justify your answer.

4. (30 points) Prove or disprove: Theorem 6–1 holds for Biba’s ring policy (described in Section 6.2.2).

Extra Credit

Remember that extra credit scores are not added to your homework score. They are recorded separately and used to determine whether to boost your grade if the score is on a borderline.

1. (30 points) Generalize the give-read rule (in section 5.2.4.2) to give-write and give-append, and prove they preserve the simple security condition, the *-property, and the discretionary security property.

Matt Bishop Office: 2209 Watershed Sciences Phone: +1 (530) 752-8060 Email: mabishop@ucdavis.edu

ECS 235B, Foundations of Computer and Information Security Version of April 9, 2026 at 4:39PM

You can also obtain a PDF version of this.