Fingerprint Scheduling @ Crypto Working Group, Utrecht, May 2015

This talk explains Fingerprint scheduling, a scheduling algorithm for Dining Cryptographers networks, and outlines its characteristics compared to other scheduling algorithms.

I gave this talk at the Cryptography Working Group meeting in May 2015. See http://www.win.tue.nl/eipsi/cwg/aank%20mei%202015.pdf for the full program.

Transcript

1. Fingerprint Scheduling for dining-cryptographer networks peter@cryptojedi.org Moritz Neikes Peter Schwabe Anna Krasnova anna@mechanical-mind.org m.neikes@student.ru.nl Radboud Universiteit Nijmegen 1/70
2. Vimbodia Great Kingdom of Emacston 2/70
3. Vimbodia Great Kingdom of Emacston 3/70
4. https://xkcd.com/378/ 4/70
5. Vimbodia Great Kingdom of Emacston 5/70
6. Vimbodia Great Kingdom of Emacston $#@&*! 6/70
7. Problem Many users Unstable connections even against very strong adversaries Anonymous communication 7/70
8. DC networks (Chaum, 1988) 8/70
9. Charlie Alice Bob 9/70
10. Charlie Alice Bob 0 1 1 10/70
11. Charlie Alice Bob 0 1 1 key 11/70
12. Charlie Alice Bob 0 1 1 0 1=1 0 1=1 1 1=0 0 1 1 12/70
13. Charlie Alice Bob 0 1 1 0 1=1 0 1=1 1 1=0 0 1 1 0 1=0 1 result 13/70
14. Charlie Alice Bob 0 1 1 0 1=1 0 1=1 1 1=0 0 0 1 sending 14/70
15. Charlie Alice Bob 0 1 1 0 1=1 0 1=1 1 1=0 0 0 1 0 0=1 1 sending 15/70
16. More Bits 16/70
17. Charlie Alice Bob 100110 100110 111110 100110 001010 100110 110100 110100 001010 111110 101100 010010 000000 111110 101100 010010 100110 001010 101100 110100 100110 010010 17/70
18. Charlie Alice Bob 100110 100110 111110 100110 001010 100110 110100 110100 001010 111110 101100 111000 101010 111110 101100 111000 100110 001010 101100 110100 100110 010010 18/70
19. Charlie Alice Bob 100110 100110 100110 001010 100110 110100 110100 001010 111110 101100 111000 001011 011111 011111 101100 111000 100110 001010 101100 110100 100110 010010 collision 19/70
20. Multiple senders Collision Corruption Retransmission Wasted traffic Inefficient Collisions 20/70
21. BAD Multiple senders Collision Corruption Retransmission Wasted traffic Inefficient Collisions 21/70
22. WORSE More users More collisions More corruption More traffic waste Collisions 22/70
23. Unconditional anonymity Collisions Recap Arbitrary messages Many participants High traffic load DC networks: 23/70
24. Scheduling 24/70
25. 101100 011010 011110 schedule 101000 000000 000000 000000 000000 000000 000000 1 6 5 4 3 2 slot reserve 25/70
26. Collisions during reservation? 101100 011010 110110 000000 Detectable Undetectable 100100 011010 110110 001000 More slots! Herbivore 26/70
27. Herbivore http://www.cs.cornell.edu/People/egs/papers/herbivore-tr.pdf small sub-nets More Slots! doesn't scale Goel, Robson, Polte, Sirer 2003 Divide-and-conquer not relevant Disconnected users: more slots than needed Inactive users: ~1000 #users small anonymity set :( 27/70
28. Herbivore doesn't scale Goel, Robson, Polte, Sirer 2003 28/70
29. Tree-like collision resolution with superposed receiving http://dud.inf.tu-dresden.de/sirene/publ/Pfit_88_0.pdf Andreas Pfitzmann, 1990 _6.pdf ... 29/70
30. Pfitzmann's algorithm http://dud.inf.tu-dresden.de/sirene/publ/Pfit_88_0.pdf Finite field addition Andreas Pfitzmann, 1990 _6.pdf ... Pick slot Slot index through DC-net 30/70
31. Alice: Bob: Charlie: 3 7 2 1...12 slots 1 1 1 12 3 31/70
32. Alice: Bob: Charlie: 3 7 2 1...12 slots 1 1 1 12 3 12/3 =4 32/70
33. Alice: Bob: Charlie: 3 7 2 1...12 slots 1 1 1 12 3 12/3 =4 3 0 2 1 0 1 5 2 33/70
34. Alice: Bob: Charlie: 3 7 2 1...12 slots 1 1 1 12 3 12/3 =4 3 0 2 1 0 1 5 2 5/2 =2 0 0 2 0 0 1 2 1 34/70
35. Alice: Bob: Charlie: 3 7 2 1...12 slots 1 1 1 12 3 12/3 =4 3 0 2 1 0 1 5 2 5/2 =2 0 0 2 0 0 1 2 1 2 public 35/70
36. Alice: Bob: Charlie: 3 7 2 1...12 slots 1 1 1 12 3 12/3 =4 3 0 2 1 0 1 5 2 5/2 =2 0 0 2 0 0 1 2 1 7 3 2 public 36/70
37. Alice: Bob: Charlie: 3 3 11 1...12 slots 1 1 1 17 3 17/3 =5 3 3 0 1 1 0 6 2 6/2 =3 3 3 0 1 1 0 6 2 3 collision 11 37/70
38. Pfitzmann's algorithm http://dud.inf.tu-dresden.de/sirene/publ/Pfit_88_0.pdf Inactive users: Andreas Pfitzmann, 1990 _6.pdf ... Utilizes message collisions no additional costs No undetectable conflicts 38/70
39. unstable connections 39/70
40. Pfitzmann's algorithm http://dud.inf.tu-dresden.de/sirene/publ/Pfit_88_0.pdf Inactive users: Andreas Pfitzmann, 1990 Disconnected users: _6.pdf ... Utilizes message collisions no additional costs breaks protocol No undetectable conflicts 40/70
41. Alice: Bob: Charlie: 3 7 2 1...12 slots 1 1 1 12 3 12/3 =4 3 0 2 1 0 1 5 2 5/2 =2 0 0 2 0 0 1 2 1 41/70
42. up to n messages for n users reserve Joining delay linear in # users 42/70
43. Herbivore doesn't scale Goel, Robson, Polte, Sirer 2003 Pfitzmann's algorithm Andreas Pfitzmann, 1990 breaks on disconnect 43/70
44. Dissent http://dedis.cs.yale.edu/dissent/files/dissent.pdf Corrigan-Gibbs, Ford 2010 Accountable Two modes: shuffle bulk Anonymity by shuffle 44/70
45. Dissent http://dedis.cs.yale.edu/dissent/files/dissent.pdf Corrigan-Gibbs, Ford 2010 Alice: Bob: Charlie: (simplified!) m A m B m C m A m B m C m A m B m C m A m B m C 45/70
46. Dissent http://dedis.cs.yale.edu/dissent/files/dissent.pdf Corrigan-Gibbs, Ford 2010 Shuffle Guaranteed sending Bulk variable message length big computational overhead fixed message length side-channel 46/70
47. Herbivore doesn't scale Goel, Robson, Polte, Sirer 2003 Pfitzmann's algorithm Andreas Pfitzmann, 1990 breaks on disconnect Dissent Corrigan-Gibbs, Ford 2010 hard to implement breaks on disconnect 47/70
48. Vimbodia Great Kingdom of Emacston :( 48/70
49. Collisions during reservation? 101100 011010 110110 000000 Detectable Undetectable 100100 011010 110110 001000 More slots! More bits! Fingerprint scheduling 49/70
50. Fingerprint scheduling More bits per slot 2 bits for now More choices Flip left / right / both bit(s) detect more collisions 50/70
51. 10.00.00 00.00.10 11.01.10 01.01.00 Alice: Bob: Charlie: 10 11 01 fingerprint 3 slots 51/70
52. 10.00.00 00.00.10 11.01.10 01.01.00 Alice: Bob: Charlie: 10 11 01 taken free 52/70
53. 01.11.11 01.01.01 11.10.00 11.00.10 01.01.00 Alice: Bob: Charlie: 01 11 11 previously II. 53/70
54. 10.10.10 10.11.01 01.11.01 11.00.10 01.01.00 01.10.10 Alice: Bob: Charlie: 10 10 01 previously III. 54/70
55. 10.10.10 10.11.01 01.11.01 11.00.10 01.01.00 01.10.10 Alice: Bob: Charlie: 10 10 01 previously III. converged! 55/70
56. 10.10.10 10.11.01 01.11.01 11.00.10 01.01.00 01.10.10 Alice: Bob: Charlie: 10 10 01 previously III. converged! 01.10.10 000000 000000 000000 1 3 2 56/70
57. Fingerprint scheduling Iterate Discussion bits b slots, choose one s 57/70
58. 100110 START PICK FREE SLOT COLLISION? TOSS COIN FREE SLOT? 100110 BACK OFF NO YES MOVE YES STAY NO PICK FINGERPRINT 58/70
59. 100110 START PICK FREE SLOT COLLISION? TOSS COIN FREE SLOT? 100110 BACK OFF NO YES MOVE YES STAY NO PICK FINGERPRINT 10.00.00 00.00.10 11.01.10 01.01.00 59/70
60. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 inactive 1,000 users 16 slots 60/70
61. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 inactive 1,000 users 16 slots 61/70
62. reserve Joining delay constant 62/70
63. Fingerprint scheduling Iterate Discussion bits b slots, choose one s Inactive users: no additional costs Disconnected users: compensated immediately 63/70
64. Vimbodia Great Kingdom of Emacston : ) 64/70
65. THE VERY INCOMPLETE MATRIX OF DC-NETWORK SOLUTIONS AND THEIR PROPERTIES 65/70
66. Guaranteed Sending Adapt to load balance Equal throughput Catch disruptors False accusation Computational overhead Disconnected users PFITZMANN INHERENT EXTERNAL PROTOCOL LITTLE RESTART HERBIVORE ESTIMATED NONE IRRELEVANT FINGERPRINT INHERENT LITTLE COMPENSATED DISSENT SHUFFLE BULK MANUAL INHERENT NEVER LARGE MASSIVE RESTART EXTERNAL PROTOCOL EXTERNAL PROTOCOL 66/70
67. Fingerprint scheduling Scales with # active users Fast, even in large networks Stable under disconnections Simple to implement No computational overhead m.neikes@student.ru.nl No more war about editors 67/70
68. Traditional alg. Bit-map protocols Tokens (slotted) ALOHA CSMA Carrier Sense Multiple Access Collision resolution Collision-free doesn't scale inefficient no anonymity 68/70
69. Alice Bob Charlie 100110 100110 100110 001010 100110 110100 Fred George 100110 110111 100110 011001 100110 101110 69/70
70. Alice Bob Charlie 100110 100110 100110 001010 100110 110100 Fred George 100110 011001 100110 101110 70/70