Lecture7 –More on Attacks

1. Lecture7 –More on Attacks Rice ELEC 528/ COMP 538 Farinaz Koushanfar Spring 2009

2. Outline • More on side-channel attacks • Fault injection attacks • Generic attacks on cryptosystems Slides are mostly courtesy of Michael Tunstall michael.tunstall@gemplus.com

3. Simple power analysis (SPA) - example

4. SPA example (cont’d)

5. SPA example (cont’d) • Unprotected modular exponentiation – square and multiply algorithm

6. Possible counter measure – randomizing RSA exponentiation

7. Statistical power analysis • Two categories • Differential power analysis (DPA) • Correlation power analysis (CPA) • Based on the relationship b/w power consumption & hamming weight of the data

8. Modeling the power consumption • Hamming weight model • Typically measured on a bus, Y=aH(X)+b • Y: power consumption; X: data value; H: Hamming weight • The Hamming distance model • Y=aH(PX)+b • Accounting for the previous value on the bus (P)

9. Differential power analysis (DPA) • DPA can be performed in any algo that has operation =S(K), •  is known and K is the segment key The waveforms are caotured by a scope and Sent to a computer for analysis

10. What is available after acquisition?

11. DPA (cont’d) The bit will classify the wave wi • Hypothesis 1: bit is zero • Hypothesis 2: bit is one • A differential trace will be calculated for each bit!

12. DPA (cont’d)

13. DPA (cont’d)

14. DPA -- testing

15. DPA -- testing

16. DPA – the wrong guess

17. DPA (cont’d) • The DPA waveform with the highest peak will validate the hypothesis

18. DPA curve example

19. DPA (cont’d)

20. Attacking a secret key algorithm

21. Typical DPA Target

22. Example -- DPA

23. Example – hypothesis testing

24. DPA (Cont’d)

25. DPA on DES algorithm

26. DPA on other algorithms

27. Correlation power analysis (CPA) • The equation for generating differential waveforms replaced with correlations • Rather than attacking one bit, the attacker tries prediction of the Hamming weight of a word (H) • The correlation is computed by:

28. Statistical PA -- countermeasures

29. Anti-DPA countermeasures

30. Anti-DPA • Internal clock phase shift

31. DPA summary

32. Electromagnetic power analysis

33. EMA – probe design

34. EMA signal

35. Spatial positioning

36. Spatial positioning

37. Example: SEMA on RSA

38. EMA (cont’d)

39. Counter measures

40. Fault injection attacks

41. Fault attacks

42. Fault injection techniques • Transient (provisional) and permanent (destructive) faults • Variations to supply voltage • Variations in the external clock • Temperature • White light • Laser light • X-rays and ion beams • Electromagnetic flux

43. Need some (maybe expensive equipment) – eg, laser

44. Fault injection steps

45. Provisional faults • Single event upsets • Temporary flips in a cell’s logical state to a complementary state • Multiple event faults • Several simultaneous SEUs • Dose rate faults • The individual effects are negligible, but cumulative effect causes fault • Provisional faults are used more in fault injection

46. Permanent faults • Single-event burnout faults • Caused by a parasitic thyristor being formed in the MOS power transistors • Single-event snap back faults • Caused by self-sustained current by parasitic bipolar transistors in MOS • Single-event latch-up faults • Creates a self sustained current in parasitics • Total dose rate faults • Progressive degradation of the electronic circuit

47. Fault impacts (model) • Resetting data • Data randomization – could be misleading, no control over! • Modifying op-code – implementation dependent

48. Fault attacks – counter measures

49. Fault attacks – counter measures

50. Attacks on systems using smart cards