ACCESS – distributed management group Mads Dam KTH/CSC
Goal: To preserve some desired property as far as possible in face of attack Confidentiality:
. .
Everything must be fixed:
2 1 c a c b a 3 b a
Pro. Verif: Constraint-based tool developed by B. Blanchet Successfully used for verification of complex protocols in applied pi Examples: Just Fast Keying – complex authentication protocol Protocol for certified email Rationale for success: Very rudimentary control flow in protocols No branching on secrets Remaining challenges: Multiple sessions/agents, richer control flow, cryptographic soundness
Agent Property of agents state
State: Assignment of terms to variables x = enc(y, pk(z)) y = pair(0, 1) z=c All operations and public constants are one-way computable Different agents have access to different variables A knows F in state s: F holds at all global states s’ that A cannot distinguish from s
A can distinguish global states s, s’: Same equations hold for A in s and s’ Static equivalence in applied pi Computationally justified semantics for BAN logic Complete axiomatization of validity For some theories, cryptographic soundness through link to applied pi: A knows F at s if and only if F holds at all states that are computationally indistinguishable from s in sense of cryptography
Single-session, approximate analysis of industry-scale security protocols becoming feasible - ”Static” protocols - Limited control flow, no recursion, no concurrency - Cf. Avispa project site Cryptographic analysis remains complex and error-prone Cryptographic soundness active research area - May become feasible in limited applications Main challenge, cf. ACCESS: - Lifting analysis techniques to dynamic and concurrent systems
Example: Epidemic protocols At round 0: Local estimate = local value At round n+1: Neighbours exchange + average local estimates Local value leaked at step 1 Or when local value changes Is it possible to aggregate without leaking information?
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