1. Memory-based DoS and Deanonymization Attacks on Tor DCAPS Seminar October 11 th, 2013 Rob Jansen U.S. Naval Research Laboratory rob.g.jansen@nrl.navy.mil *Joint with Aaron Johnson, Florian Tschorsch, Björn Scheuermann

2. The Tor Anonymity Network torproject.org

3. How Tor Works

7. Tor protocol aware

8. Tor Flow Control exit entry

9. Tor Flow Control One TCP Connection Between Each Relay, Multiple Circuits exit entry

10. Tor Flow Control One TCP Connection Between Each Relay, Multiple Circuits Multiple Application Streams exit entry

11. Tor Flow Control No end-to-end TCP! exit entry

12. Tor Flow Control Tor protocol aware exit entry

13. Tor Flow Control Packaging End Delivery End exit entry

14. Tor Flow Control Packaging End Delivery End exit entry

15. Tor Flow Control 1000 Cell Limit SENDME Signal Every 100 Cells exit entry

16. Outline ● The Sniper Attack – Low-cost memory consumption attack that disables arbitrary Tor relays ● Deanonymizing Hidden Services – Using DoS attacks for deanonymization ● Countermeasures

17. The Sniper Attack Start Download Request exit entry

18. The Sniper Attack Reply DATA exit entry

19. The Sniper Attack Package and Relay DATA DATA exit entry

20. The Sniper Attack DATA Stop Reading from Connection DATA R exitentry

21. The Sniper Attack DATA R exit entry Flow Window Closed

22. The Sniper Attack DATA Periodically Send SENDME SENDME R DATA exit entry

23. The Sniper Attack DATA Periodically Send SENDME SENDME R DATA exit entry Flow Window Opened

24. The Sniper Attack DATA R exit entry DATA Out of Memory, Killed by OS

25. The Sniper Attack DATA R exit entry DATA Use Tor to Hide

26. Memory Consumed over Time

27. Mean RAM Consumed, 50 Relays

28. Mean BW Consumed, 50 Relays

29. Speed of Sniper Attack DirectAnonymous Relay GroupsSelect %1 GiB8 GiB1 GiB8 GiB Top Guard1.7 Top 5 Guards6.5 Top 20 Guards19 Top Exit3.2 Top 5 Exits13 Top 20 Exits35 Path Selection Probability ≈ Network Capacity

30. Speed of Sniper Attack DirectAnonymous Relay GroupsSelect %1 GiB8 GiB1 GiB8 GiB Top Guard1.70:010:180:020:14 Top 5 Guards6.50:081:030:121:37 Top 20 Guards190:455:581:078:56 Top Exit3.20:010:080:010:12 Top 5 Exits130:050:370:070:57 Top 20 Exits350:293:500:445:52 Time (hours:minutes) to Consume RAM

31. Speed of Sniper Attack DirectAnonymous Relay GroupsSelect %1 GiB8 GiB1 GiB8 GiB Top Guard1.70:010:180:020:14 Top 5 Guards6.50:081:030:121:37 Top 20 Guards190:455:581:078:56 Top Exit3.20:010:080:010:12 Top 5 Exits130:050:370:070:57 Top 20 Exits350:293:500:445:52 Time (hours:minutes) to Consume RAM

32. Speed of Sniper Attack DirectAnonymous Relay GroupsSelect %1 GiB8 GiB1 GiB8 GiB Top Guard1.70:010:180:020:14 Top 5 Guards6.50:081:030:121:37 Top 20 Guards190:455:581:078:56 Top Exit3.20:010:080:010:12 Top 5 Exits130:050:370:070:57 Top 20 Exits350:293:500:445:52 Time (hours:minutes) to Consume RAM

33. Outline ● The Sniper Attack – Low-cost memory consumption attack that disables arbitrary Tor relays ● Deanonymizing Hidden Services – Using DoS attacks for deanonymization ● Countermeasures

34. Hidden Services HS User wants to hide service

35. Hidden Services entry IP HS chooses and publishes introduction point IP HS

36. Hidden Services entry IP HS Learns about HS on web

37. entry Hidden Services entry IP HS Builds Circuit to Chosen Rendezvous Point RP RP

38. entry Hidden Services entry IP HS Notifies HS of RP through IP RP entry RP

39. entry Hidden Services entry IP HS RP

40. entry Hidden Services entry IP HS Build New Circuit to RP RP entry RP

41. entry Hidden Services entry IP HS Communicate! RP entry RP

42. entry Deanonymizing Hidden Services HS RP

43. entry Deanonymizing Hidden Services HS RP Also runs a guard relay

44. entry Deanonymizing Hidden Services entry HS RP Build New Circuit to RP

45. entry Deanonymizing Hidden Services entry HS RP S&P 2006, S&P 2013

46. entry Deanonymizing Hidden Services entry HS RP S&P 2013 PADDIN G Send 50 Padding Cells

47. entry Deanonymizing Hidden Services entry HS RP Identify HS entry if cell count = 52 S&P 2013

48. entry Deanonymizing Hidden Services entry HS RP Sniper Attack, or any other DoS

49. entry Deanonymizing Hidden Services HS RP Choose new Entry Guard

50. entry Deanonymizing Hidden Services HS RP

51. entry Deanonymizing Hidden Services HS RP S&P 2006, S&P 2013

52. entry Deanonymizing Hidden Services HS RP Send 50 Padding Cells S&P 2013 PADDIN G

53. entry Deanonymizing Hidden Services HS RP Identify HS if cell count = 53 S&P 2013

54. Outline ● The Sniper Attack – Low-cost memory consumption attack that disables arbitrary Tor relays ● Deanonymizing Hidden Services – Using DoS attacks for deanonymization ● Countermeasures

55. Countermeasures ● Sniper Attack Defenses – Authenticated SENDMEs – Queue Length Limit – Adaptive Circuit Killer ● Deanonymization Defenses – Entry-guard Rate-limiting – Middle Guards

56. Questions? cs.umn.edu/~jansen rob.g.jansen@nrl.navy.mil think like an adversary

57. Speed of Deanonymization Guard BW (MiB/s) Guard Probability (%) Average # Rounds Average # Sniped Average Time (h) 1 GiB Average Time (h) 8 GiB 8.410.486613346279 16.650.97397923149 31.651.924481384 66.043.81326644 96.615.4919531 1 GiB/s Relay Can Deanonymize HS in about a day

58. Circuit Killer Defense

59. The Sniper Attack exit entry exitentry Single Adversary

60. The Sniper Attack exit entry exitentry Anonymous Tunnel

61. The Sniper Attack exit entry exitentry

62. The Sniper Attack exit entry exitentry DATA

63. The Sniper Attack exit entry exitentry DATA R

64. The Sniper Attack exit entry exitentry DATA R Flow Window Closed

65. The Sniper Attack exit entry exitentry DATA R R

66. The Sniper Attack exit entry exitentry DATA R R

67. The Sniper Attack exit entry exitentry DATA R R Killed by OS DATA