January 25, 2021 Outline

Reading: text, §5.2
Due: Homework #2, due February 5; Project progress report, due February 12

1. Bell-LaPadula: formal model
   1. Elements of system: s_i ∈ S subjects, o_i ∈ O objects
   2. State space V = B × M × F × H where:
      B set of current accesses (i.e., access modes each subject has currently to each object);
      M access permission matrix;
      F consists of 3 functions: f_s is security level associated with each subject, f_o security level associated with each object, and f_c current security level for each subject;
      H hierarchy of system objects, functions h: O→P(O) with two properties:
      1. If o_i ≠ o_j, then h(o_i) ∩ h(o_i) = ∅
      2. There is no set { o₁, …, o_k } ⊆ O such that for each i, o_i+1 ∈ h(o_i) and o_k+1 = o₁
   3. Set of requests is R
   4. Set of decisions is D
   5. W = R × D × V × V is motion from one state to another
   6. System Σ(R, D, W, z₀) ⊆ X × Y × Z such that (x, y, z) ∈ Σ(R, D, W, z₀) iff (x_t, y_t, z_t, z_t−1) ∈ W for each t ∈ T; latter is an action of system
   7. Theorem: Σ(R, D, W, z₀) satisfies the simple security condition for any initial state z₀ that satisfies the simple security condition iff W satisfies the following conditions for each action (r, d, (b′, m′, f′, h′), (b, m, f, h)):
      1. each (s, o, x) ∈ b′ − b satisfies the simple security condition relative to f′ (i.e., x is not read, or x is read and f_s(s) dom f_o(o)); and
      2. if (s, o, x) ∈ b does not satisfy the simple security condition relative to f′, then (s, o, x) ∉ b′
   8. Theorem: Σ(R, D, W, z₀) satisfies the *-property relative to S′ ⊆ S for any initial state z₀ that satisfies the *-property relative to S′ iff W satisfies the following conditions for each (r, d, (b′, m′, f′, h′), (b, m, f, h)):
      1. for each s ∈ S′, any (s, o, x) ∈ b′ − b satisfies the *-property with respect to f′; and
      2. for each s ∈ S′, if (s, o, x) ∈ b does not satisfy the *-property with respect to f′, then (s, o, x) ∉ b′
   9. Theorem: Σ(R, D, W, z₀) satisfies the ds-property iff the initial state z₀ satisfies the ds-property and W satisfies the following conditions for each (r, d, (b′, m′, f′, h′), (b, m, f, h)):
      1. if (s, o, x) ∈ b′ − b, then x ∈ m′[s, o]; and
      2. if (s, o, x) ∈ b and x ∈ m′[s, o], then (s, o, x) ∉ b′
   10. Basic Security Theorem: A system Σ(R, D, W, z₀) is secure iff z₀ is a secure state and W satisfies the conditions of the above three theorems for each action.
   11. Using the model
       1. Define ssc-preserving, *-property-preserving, ds-property-preserving
       2. Define relation W(ω)
       3. Show conditions under which rules are ssc-preserving, *-property-preserving, ds-property-preserving
       4. Show when adding a state preserves those properties
       5. Example instantiation: get-read for Multics

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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 January 21, 2021 at 10:07AM

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