Homework #2

Due: April 28, 2025
Points: 100

Questions

1. (20 points) Consider the construction of the three-parent joint creation operation from the two-parent joint creation operation shown in Section 3.5.2. One paper had cr_C(s, c) = c/R₃ and link₂(S, A₃) = A₃/t ∈ dom(S). Why is this not sufficient to derive the three-parent joint creation operation from the two-parent joint creation operation?

2. (18 points) Given the security levels L₄, L₃, L₂, L₁, and L₀ (ordered from highest to lowest), and the categories C₁, C₂, and C₃, specify what type of access (read, write, both, or neither) under the Bell-LaPadula model is allowed in each of the following situations. Assume that discretionary access controls allow anyone access unless otherwise specified.
   1. Tom, cleared for (L₄, {C₂, C₃}), wants to access a document classified (L₃, {C₂}}.
   2. Annie, cleared for (L₂, {C₁}), wants to access a document classified (L₂, {C₂}).
   3. Katie, cleared for (L₀, {C₃}), wants to access a document classified (L₄, {C₁, C₃}).
   4. Paul, cleared for (L₃, {C₁, C₂}, wants to access a document classified (L₃, {C₁, C₂}).
   5. Judy, cleared for (L₄, {C₁, C₂, C₃}), wants to access a document classified (L₃, {C₁, C₂}).
   6. Sylvester, cleared for (L₀, ∅) wants to access a document classified (L₄, {C₃}).

3. (18 points) Repeat the above question, but under the Biba Strict Integrity Policy model rathe than the Bell-LaPadula model.

4. (20 points) Prove Theorem 6.1 for the strict integrity policy of Biba’s model.

5. (14 points) In the Clark-Wilson model, must the TPs be executed serially, or can they be executed in parallel? If the former, why; if the latter, what constraints must be placed on their execution?

6. (10 points) In the Brewer-Nash (Chinese Wall) model, why must sanitized objects be in a single company dataset in their own conflict of interest class, and not in the company dataset corresponding to the institution producing the sanitized object?

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 15, 2025 at 10:40PM

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