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FSE 2018 Modes of operations for computing on encrypted data Dragos Rotaru, N.P. Smart, and Martijn Stam KU Leuven, University of Bristol 1 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering Multiparty computation


  1. FSE 2018 Modes of operations for computing on encrypted data Dragos Rotaru, N.P. Smart, and Martijn Stam KU Leuven, University of Bristol 1 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  2. Multiparty computation hijacks FSE’18 a c b Goal : Compute F(a, b, c) Dragos Rotaru 2 2 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  3. What is the problem? 3 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  4. What is the problem? 42 42 42 42 4 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  5. What is the problem? 42 42 42 42 Enc Enc Enc 5 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  6. What is the problem? 42 42 42 Enc(42) 6 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  7. What is the problem? 42 42 42 Enc(42) 7 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  8. What is the problem? 42 42 42 Tag(E(42)) Enc(42) 8 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  9. What is the problem? For free: detect malicious encryption keys. Tag(E(42)) Enc(42) 9 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  10. Prior work – PRFs in MPC (CCS’16) Tag(Enc(42)) Enc(42) - MiMC - Legendre PRF 10 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  11. Prior work – PRFs in MPC (CCS’16) Tag(Enc(42)) Enc(42) M[1] Enc 11 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  12. Prior work – PRFs in MPC (CCS’16) Tag(Enc(42)) Enc(42) M[1] M[2] + Enc Enc 12 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  13. Prior work – PRFs in MPC (CCS’16) Tag(Enc(42)) Enc(42) M[1] M[2] M[3] + + Enc Enc Enc 13 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  14. Prior work – PRFs in MPC (CCS’16) Tag(Enc(42)) Enc(42) M[1] M[2] M[3] M[4] + + + Tag Enc Enc Enc Enc 14 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  15. What we have done [42] Enc(42) Tag(42) • Analyze AE in Multiparty Computation (MPC). • Useful MPC happens in Fp => Need AE and PRFs modp. • Look for parallel AE: CTR+PMAC, OTR. 15 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  16. The story This Photo by Unknown Author is licensed under CC BY-NC-ND 16 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  17. The story ‘You take the blue pill— the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill — you stay in Wonderland, and I show you how deep the rabbit hole goes.’ 17 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  18. The story ‘You take the blue pill— the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill — you stay in Wonderland, and I show you how deep the rabbit hole goes.’ 18 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  19. Down the rabbit hole - MPC with Secret Sharing 𝑦 ← 𝑦 2 𝑦 = 𝑦 1 + ⋯ + 𝑦 𝑜 𝑦 ← 𝑦 1 Each 𝑄 𝑗 has 𝑦 ← 𝑦 𝑗 𝑦 ← 𝑦 3 19 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  20. MPC Preprocessing Phase Generate triples [c] = [a][b] 20 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  21. MPC Preprocessing Phase Generate triples [c] = [a][b] 21 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  22. MPC Preprocessing Phase 22 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  23. MPC Preprocessing Phase 23 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  24. MPC Online Phase Use Triples. 24 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  25. MPC Online Phase Use Triples. 25 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  26. MPC Circuit Evaluation X Z Y Z X Y 26 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  27. MPC Circuit Evaluation Z X Y 27 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  28. MPC Circuit Evaluation Z X Y 28 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  29. MPC Circuit Evaluation Z X Y 29 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  30. MPC Circuit Evaluation 3 triples. 2 comm. rounds Z X Y 30 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  31. Tweak your encryption to MPC Reveal 31 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  32. Tweak your encryption to MPC 32 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  33. Tweak your encryption to MPC 33 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  34. How-to compute PMAC 34 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  35. Let’s do AE with CTR+pPMAC 35 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  36. Let’s do AE with CTR+pPMAC 36 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  37. When ideal meets real 37 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  38. When ideal meets real – surprise! 38 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  39. When ideal meets real – surprise! Legendre MiMC 39 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  40. Other competitive modes 40 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  41. Other competitive modes 41 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  42. Some open problems • Preprocessing scales linearly in terms of number of message blocks - roughly n PRFs for n messages. • Number of rounds of a cipher vs. multiplicative depth in MPC. 42 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  43. Thank you! 43 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

  44. Thank you! • Questions? 44 Dragos Rotaru , N.P. Smart, M. Stam imec-Cosic, Dept. Electrical Engineering

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