ITIS 3200: Introduction to Information Security and Privacy

1. ITIS 3200:Introduction to Information Security and Privacy Dr. Weichao Wang

2. Chapter 2: A concrete example: Access Control Matrix • First introduced in OS and databases • Describe allowed access using a matrix • Protection state of the system • Describe the protection state by characterizing rights of each subject over objects. • We are especially interested in state transitions that will affect the protection states.

3. Access control matrix model • Objects O: the set of protected entities • Subjects S: the set of active objects that can perform actions (process or user) • Rights R: the full right set. For every pair (s, o), a subset of rights is granted. • The set of protection states is represented by (S, O, A) • Some subjects can also be objects • An example

4. Access control matrix model (continued) • The meaning of rights depends on system and objects involved • The access control matrix can model a large system containing multiple machines, or a programming language at the micro level • The matrix can also contain functions to determine rights (mutual access)

5. Protection state transitions • Operations will lead to changes of states, and updates in access control matrix • State Xi will change to state X(i+1) under command c(i+1) • A command may have multiple parameters and lead to multiple state transitions (share a folder in a OS)

6. Primitive command • Create subject s • Create object o • Enter right r into a[s, o] • Delete right r from a[s, o] • Destroy subject s • Destroy object o

7. Primitive commands can be combined into commands • System usually does not directly call primitive commands, but through another level of wrapper • A command invoking only one primitive is called mono-operational command • Conditional commands do not support negation

8. Examples of commands Command create-file (p, f) // process p creates a file f create object f; enter own into a[p, f]; enter read into a[p, f]; enter write into a[p, f]; End Command grant-read-file (p, f, q) // process p grants read if r in a[p, f] and owner in a[p, f] // right on file f to q then enter r into a[q, f]; end

9. Some concepts that we need to understand: • Protection state and access control matrix • State transition caused by operations and command • Access control matrix is not used directly because of space requirements.