1 ISA 562 Internet Security Theory and Practice Midterm Exam Review

2 Review for the Mid-term First five chapters + Cryptography The nature of the exam: 4-5 questions Similar to the homework May have some modeling, some policy, some descriptions

3 Review Chapter 1 + Transparency CIA of Information Security What they are Given a set of requirements, can we categorize them? Access control matrix Safe state Safe state written as a (pre-condition, post condition) pair of read, write and access operations Add/delete rights Add/delete subjects, objects and operations

4 Review Chapter 1 Continued … Mono Operational Commands Single operations like add “ make P the owner of file Q ” Written formally as make.owner(p,q) Conditional commands “ If p owns f, then let p give r rights to q ” How to write them formally Multiple conditions …

5 Review of Chapter 2: Foundations ACM, ACL and capabilities Turing machines Un-decidability HRU Result: Is there an algorithm, that given an initially safe state halts and say yes/no to the safety after granting a generic right r ? Method: Encode safety, granting rights etc as Turing machine instructions Special cases are decidable: Take-grant model

6 Review of Chapter 2: Foundations Capability based systems Lock and key model Lock=object, key=subject Object carries permissions = subject presents key to unlock object

7 Review of Chapter 3: Policies Formalization of security policy using precise policy languages DAC, MAC and RBAC Specification of DAC using subjects objects and access rights

8 Review: MAC Review and background Lattices Military systems and Denning ’ s Axioms Bell-LaPadula (BLP) Policy Step 1 – clearance/classification Step 2 – categories Example System – DG/UX Tranquility Controversy at a glance

9 Supremas and Infimas of POsets Definition: (A,<) is a POset and B  A Say that b 0  A is a Least upper bound (aka Supemum) of B iff (1) b 0 is an upper bound and (2) b 0 <b for all other upper bounds b of B B1, B2, B3 B4 B5 B6 b1,b2, b3 b0 Upper bounds Lower bounds c0 c2, c3, c4 The set B Say that c 0  A is a greatest lower bound (Infimum) iff (1) c 0 is an upper bound (2)c 0 <b for all other lower bounds c of B

10 Example Lattices – Power Set Lattice S = {a,b,c} 2 S = { ,{a},{b},{c},{a,b},{b,c},{a,c},{a,b,c} } Arrows mean  (informally, included by) Special case: Total order Partial order Special case: Lattice

11 Example Product Lattice Lattice 1 (arrow means  ) Lattice 2  Lattice 1 x,y  x ’,y ’ means y ’  y and x  x ’ Lattice 2 (arrow means  )

12 BLP Rules Simple Security Policy No Read up * Security Property No write down

13 Cryptography Major uses: Confidentiality Nonrepudiation Authentication Access Control The major types: Substitution Symmetric Asymmetric RSA Diffie Hellman