Alternative architectures for distributed ledgers. Sarah Meiklejohn (University College London)

Transcription

1 Alternative architectures for distributed ledgers Sarah Meiklejohn (University College London)

2 company company data consumers data producers company company (icons by parkjisun from noun project) 2

3 data consumers data producers (icons by parkjisun from noun project) 3

4 top ten obstacles for blockchains 10 usability 9 governance 8 comparisons 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy 1 scalability 4

5 10 usability 9 governance 8 comparisons 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy 1 scalability 5

6 Bitcoin / blockchains / distributed ledgers mining 6

7 over 4 EH/s ( H/s) to achieve 7 tx/s! 7

8 10 usability 9 governance 8 comparisons 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy 1 scalability 8

9 full state replication 9

10 120 GB and (always) rising 10

11 10 usability 9 governance 8 comparisons 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy 1 scalability 11

12 full state replication computational power throughput 12

13 RSCoin [DM NDSS 16] RSCoin monetary supply decentralized centralized centralized ledger decentralized distributed centralized transparent? y y (or n) n pseudonyms? y y (or n) n computation high! low low 13

14 user bank 14

15 user bank 14

16 s store info only within a given shard user bank 14

17 s store info only within a given shard user bank s already reach consensus before sending info to bank 14

18 RSCoin consensus tx 4 service 2 2 tx user tx 2 3 tx: simple adaptation of Two-Phase Commit (2PC) 15

19 service user tx:

20 service user tx: 1 2 t r a n s a c t i o n s 16

21 service user tx: 1 2 t r a n s a c t i o n s 16

22 service user tx: 1 2 t r a n s a c t i o n s 16

23 service : user tx: 1 2 t r a n s a c t i o n s 16

24 service : 2 : user tx: 1 2 t r a n s a c t i o n s 16

25 1 service user 1 1 tx:

26 s check for double spending service user 1 1 tx: using lists of unspent transaction outputs (utxo) 17

27 signed yes vote service user tx:

28 service 2 2 tx user tx: bundle of evidence contains yes votes from majority of s in shard 19

29 s check validity of bundle by checking for signatures from authorized s service 2 2 tx user tx: bundle of evidence contains yes votes from majority of s in shard 19

30 and if satisfied they add transaction to be committed and send back receipt tx 4 service 2 2 tx user tx 2 3 tx:

31 security properties no double spending (if honest majority per shard) non-repudiation auditability (if s log their behavior) 21

32 consensus features conceptually simple no broadcast s communicate only with users no expensive hashing! scalable 22

33 consensus features conceptually simple no broadcast s communicate only with users no expensive hashing! scalable computational power throughput 22

34 consensus features T = set of txs generated per second Q = # s per shard M = # s comm. per per sec = tx T 2(mtx+1)Q M 23

35 consensus features T = set of txs generated per second Q = # s per shard M = # s comm. per per sec = tx T 2(mtx+1)Q M scales infinitely as more s are added! 23

36 compared to Bitcoin s 7 each new adds 75 tx/sec 24

37 user bank 25

38 user bank 25

39 Elastico [LNZBGS CCS 16] run PBFT directory committee committee member committee member committee member committee member consensus committee run PBFT 26

40 Elastico [LNZBGS CCS 16] 27

41 10 usability 9 governance 8 comparisons 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy 1 scalability 28

42 10 usability 9 governance 8 comparisons 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy 1 scalability 29

43 RSCoin [DM NDSS 16] user bank 30

44 user 31

45 user log server log log server log log server log log server log 32

46 user log server log log server log log server log log server log no unified log no need for consensus 32

47 user log server log log server log log server log log server log no unified log no need for consensus can (retroactively) detect inconsistencies between logs 32

48 transparency overlays [CM CCS 16] log server GenEventSet Log log system CheckEvidence Inspect CheckEntry monitor E BE snap auditor snap Gossip evidence 33

49 system log server log log server log log server log log server log 34

50 system log server log 34

51 GenEventSet system log server log 34

52 log server GenEventSet Log log system 34

53 log server GenEventSet Log log system CheckEntry auditor snap (meaning snap log ) auditors (efficiently) determine if events are in the log 35

54 log server GenEventSet Log log system Inspect CheckEntry monitor E BE snap auditor snap (meaning E log ) monitors (inefficiently) detect bad events in the log 36

55 log server GenEventSet Log log system CheckEvidence Inspect CheckEntry monitor E BE snap auditor snap Gossip evidence auditors and monitors ensure consistent view of log (can output evidence of inconsistencies) 37

56 security properties consistency: log server can t offer different views of log non-frameability: auditor and monitor can t frame the log accountability: log server is held to its promises 38

57 prover verifier log server log monitor E BE snap auditor snap 39

58 prover verifier log server log monitor E BE snap auditor snap 39

59 prover verifier log server log? monitor E BE snap auditor snap 39

60 prover verifier log server log?? monitor E BE snap auditor snap 39

61 prover verifier log server log?? monitor E BE snap auditor snap 39

62 prover verifier log server log?? monitor E BE snap auditor snap 39

63 prover verifier log server log monitor E BE snap auditor snap 40

64 prover verifier log server log monitor E BE snap auditor snap 40

65 prover verifier log server log?? monitor E BE snap auditor snap 40

66 prover verifier log server log?? monitor E BE snap auditor snap 40

67 prover verifier log server log?? monitor E BE snap auditor snap 40

68 prover verifier log server log?? monitor E BE snap auditor snap 40

69 Bitcoin sender miner blockchain receiver Log CheckEvidence log server log CheckEntry Inspect monitor E BE snap auditor snap Gossip evidence sender and receiver don t need to store blockchain 41

70 Bitcoin sender miner blockchain receiver Log CheckEvidence log server log CheckEntry Inspect monitor E BE snap auditor snap Gossip evidence sender and receiver don t need to store blockchain gives rise to hybrid system ( RSCoin) with no mining 41

71 Certificate Transparency [LL13] CA website client log server log Log CheckEvidence CheckEntry Inspect monitor E BE snap auditor snap Gossip evidence bad certificate issuance is exposed clients are less likely to accept bad certificates (icon by parkjisun from noun project) 42

72 CONIKS [MBBFF USENIX Sec 16] client client Inspect id provider log Log CheckEntry auditor snap (icon by parkjisun from noun project) 43

73 ARPKI [BCKPSS CCS 13] CA website client ILS log Log CheckEntry ILS log validator snap (icon by parkjisun from noun project) 44

74 ARPKI CONIKS RSCoin opaque centralized transparent decentralized what is this distance? 45

75 (transparency overlays) consistency non-frameability accountability security properties 46

76 security properties (transparency overlays) consistency non-frameability accountability (RSCoin) no double spending non-repudiation auditability 46

77 security properties (transparency overlays) consistency non-frameability accountability (RSCoin) no double spending non-repudiation auditability 46

78 security properties (transparency overlays) consistency non-frameability accountability privacy (of what)? (RSCoin) no double spending non-repudiation auditability privacy (of what)? 46

79 ARPKI CONIKS RSCoin opaque centralized transparent decentralized what is this distance? what security properties to look for? 47

80 10 usability 9 governance 8 comparisons 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy 1 scalability 48

81 10 usability 9 governance 8 comparisons 7 key management 6 agility Thanks! Any questions? 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy 1 scalability 49