1. GARBLED CIRCUITS CHECKING GARBLED CIRCUITS MORE EFFICIENT AND SECURE TWO-PARTY COMPUTATION Payman Mohassel Ben Riva University of Calgary Tel Aviv University

2. Secure Two-Party Computation Privacy: Only learn the output Correctness: Learn the intended function

3. Contributions 2PC with low overhead Input–consistency check Two-output functions New Definition Strengthen covert adversaries Better efficiency/security trade-off for practice Protocols meeting the definition

4. Garbled Circuit seed Eval() 4

5. Useful Properties 5

6. Malicious 2PC Cut-and-Choose Open Evaluate Majority Are all inputs the same? Is the output correct? Question

7. 1) Is the output correct? Open Evaluate Majority Send GOs as proof

8. 2) Is the output correct? Open Evaluate Majority Use same output labels in all circuits

9. 3) Is the output correct? Open Evaluate Majority

10. Extensions

11. Covert 2PC What about cost/pay for honest party? Question cost/pay for malicious party

12. All-or-Nothing Security

13. A Stronger Definition Increase the pay-off (of learning correct output) Orthogonal to MPC Reduce the cost of being cheated on! By strengthening the security definition

14. CovIDA Security

15. Dual-Ex 2PC Yes/no o Correctness prob. = 1-neg(k) o Leakage prob. = 1 o Bad circuit o Different inputs

16. Dual-Ex + Covert 2PC Yes/no o Correctness prob. = 1-neg(k) o Leakage prob. = 1 o Bad circuit o Different inputs

17. Dual-Ex + Covert 2PC

18. Are inputs the Same? Malicious 2PC Use same OT for x Linear in s symmetric-key Ops for input-consistency (using OT extension)

19. QUESTIONS?