Bitcoin: Synchronization and Sharing of Transactions

Transcription

1 Bitcoin: Synchronization and Sharing of Transactions Roger Wattenhofer ETH Zurich Distributed Computing Group

2

3 1200 Exchange Rate USD/BTC 1000 Price [USD/BTC]

4

5 What is Bitcoin? + + =

6 Bitcoin Basics

7 The Bank of Bitcoin

8 The Bank of Bitcoin User Balance A 2 B 5 C 8

9 The Bank of Bitcoin TX B A User Balance A 2 B 5 C 8

10 The Bank of Bitcoin TX B A User Balance A 2 4 B 5 3 C 8

11 Opening an Account in Bitcoin Private Key Public Key Address

12 Transferring Bitcoins TX: 41b221

13 Transferring Bitcoins TX: 41b B

14 Transferring Bitcoins A TX: 41b B A

15 Transferring Bitcoins A TX: 41b B A

16 Transferring Bitcoins Inputs Outputs A TX: 41b B A

17 Transferring Bitcoins A Inputs Fee TX: 41b221 Outputs 0.1 B A

18 Transferring Bitcoins Prev. TX: a1a53743 Outputs A... 1 C Inputs Fee TX: 41b221 Outputs 0.1 B A

19 Distributing the Bank TX User Balance A 2 B 5 C 8

20 Distributing the Bank

21 Distributing the Bank TX

22 Distributing the Bank TX

23 Distributing the Bank

24 Distributing the Bank

25 Let s Buy a Snack [Bamert, Decker, Elsen, W, Welten, 2013]

26 Doublespending Outputs Inputs 1 TX 1 B A

27 Doublespending Outputs Inputs 1 TX 1 B A 1 TX 1 A

28 Doublespending Outputs Inputs 1 TX 1 B A 1 TX 1 A

29 Transaction Conflicts

30 Transaction Conflicts TX TX

31 Transaction Conflicts TX TX

32 Transaction Conflicts

33 Resolving Conflicts

34 Resolving Conflicts Green!

35 Resolving Conflicts

36 How to Choose a Leader?

37 Proof-of-Work TX TX TX TX

38 Proof-of-Work Block TX TX TX TX

39 Proof-of-Work Block H(Previous Block) TX TX TX TX

40 Proof-of-Work Block H(Previous Block) TX TX TX TX H(Block) fd2e2055f117bfa261b5a6c7e11df367...

41 Proof-of-Work Block H(Previous Block) TX TX TX TX Nonce H(Block 0) 094d66aa7c844a9dbb516a41259b

42 Proof-of-Work Block H(Previous Block) TX TX TX TX Nonce H(Block 0) 094d66aa7c844a9dbb516a41259b H(Block 1) f af8bf a9259f634f...

43 Proof-of-Work Block H(Previous Block) TX TX TX TX Nonce H(Block 0) 094d66aa7c844a9dbb516a41259b H(Block 1) f af8bf a9259f634f... H(Block 2) aec87c0ca2e5eb3f f1089ada...

44 Proof-of-Work Block H(Previous Block) TX TX TX TX Nonce H(Block 0) 094d66aa7c844a9dbb516a41259b H(Block 1) f af8bf a9259f634f... H(Block 2) aec87c0ca2e5eb3f f1089ada... H(Block 3) 777f75b2a8ecfdc8026c236fc1d2ffa0.... H(Block ) d4c133672a7d657e...

45 The Blockchain Time

46 The Blockchain Time

47 Is Bitcoin stable?

48 The Blockchain Time

49 The Blockchain Time

50 Propagation Speed 0.12 Block propagation PDF Time since first observation [s] [Decker, W, 2013]

51 Propagation Speed th perc. Block propagation PDF Time since first observation [s] [Decker, W, 2013]

52 Propagation Speed th perc. Block propagation 95th perc. PDF Time since first observation [s] [Decker, W, 2013]

53 Propagation Speed 0.12 Block propagation PDF Time since first observation [s] [Decker, W, 2013]

54 Blockchain Forks 12 Blockchain forks 10 8 Forks % Blockchain Height [Decker, W, 2013]

55 Aside: Mining Evolution Hashrate PH/s Hashrate evolution

56 Aside: Mining Evolution Hashrate PH/s Hashrate evolution

57 Aside: Mining Evolution Hashrate PH/s Hashrate evolution

58 Summary Green! TX Block H(Previous Block) TX TX TX TX Nonce Time

59 How to Lose $500M

60 Addressing Transaction Malleability: MtGox has detected unusual activity on its Bitcoin wallets and performed investigations during the past weeks.

61 The MtGox Incident July 2010: First trade on MtGox May 2011: Transaction malleability identified as low priority issue February 7, 2014: MtGox halts withdrawals February 10, 2014: MtGox announces loss of 850,000 bitcoins (620 millio USD) and cites transaction malleability as root cause February 28, 2014: MtGox files for bankruptcy March : MtGox finds 200,000 bitcoins August 2015: MtGox CEO is arrested

62 Signatures 61 af bb 4d e9 f8 b e

63 Signatures af bb 4d e9 f8 b e There are multiple ways to serialize a signature: Multiple push operations (1 byte, 2 byte, 4 byte) Non-canonical DER encodings Padding...

64 Transaction Malleability Attack

65 Transaction Malleability Attack TX TX

66 Transaction Malleability Attack TX TX TX

67 Transaction Malleability Attack

68 Transaction Malleability Attack Red! TX?

69 Transaction Malleability Attack Refund

70 Incident Timeline Cumulative malleable doublespends bitcoins Feb Feb st Press Release 2nd Press Release Feb Feb Feb Feb Feb Feb Feb value number Feb transactions [Decker, W, 2014]

71 Incident Timeline Cumulative malleable doublespends bitcoins Feb Feb Feb st Press Release 2nd Press Release 386 BTC Feb Feb Feb Feb Feb Feb value number Feb transactions [Decker, W, 2014]

72 Is Bitcoin Secure?

73 Securing Your Bitcoins [Bamert, Decker, W, 2013]

74 Does Bitcoin Scale?

75 The Bitcoin Ecosystem is Growing Daily Transaction Volume Transactions

76 Scalability Limits Disk space: < 500 transactions per second

77 Scalability Limits Disk space: < 500 transactions per second Processing power: < 200 transactions per second

78 Scalability Limits Disk space: < 500 transactions per second Processing power: < 200 transactions per second Network bandwidth: < 100 transactions per second

79 Scalability Limits Disk space: < 500 transactions per second Processing power: < 200 transactions per second Network bandwidth: < 100 transactions per second Artificial 1MB limit: < 3 transactions per second

80 Scalability Limits Disk space: < 500 transactions per second Processing power: < 200 transactions per second Network bandwidth: < 100 transactions per second Artificial 1MB limit: < 3 transactions per second Today: Bitcoin: 1 transaction per second Credit Cards: > 10, 000 transactions per second

81 Payment Network

82 Payment Network

83 Payment Network

84 Micropayment Channels 5

85 Micropayment Channels 5 5

86 Micropayment Channels 5 5 T=100 5

87 Micropayment Channels 5 5 T=100 5

88 Micropayment Channels 5 5 T=100 5

89 Micropayment Channels T=100 5

90 Micropayment Channels T=100 5

91 Micropayment Channels T=100 5

92 Micropayment Channels T=100 5

93 Atomic Multiparty Opt-In

94 Atomic Multiparty Opt-In

95 Atomic Multiparty Opt-In

96 Invalidating Transactions T=100

97 Invalidating Transactions T=100 T=99

98 Bidirectional Transfers

99 Bidirectional Transfers

100 Bidirectional Transfers

101 Duplex Micropayment Channels Setup Invalidation Tree Micropayment Channels

102 Duplex Micropayment Channels T = 100 T = 100 T = 100 Setup Invalidation Tree Micropayment Channels

103 Duplex Micropayment Channels T = 100 T = 100 T = 100 T = 99 T = 100 T = 100 Setup Invalidation Tree Micropayment Channels

104 Duplex Micropayment Channels T = 100 T = 100 T = 100 T = 99 T = 100 T = 100 T = 99 T = 100 Setup Invalidation Tree Micropayment Channels

105 Duplex Micropayment Channels T = 100 T = 100 T = 100 T = 99 T = 100 T = 100 T = 99 T = 100 T = 99 Setup Invalidation Tree Micropayment Channels

106 Summary Red! T = 100 T = 100 T = 100 Refund TX? T = 99 T = 100 T = 100 T = 99 T = 100 T = 99

107 Thank you, questions? Thanks to Christian Decker ETH Zurich Distributed Computing Group

108 Securing Fast Payments

109 Let s Buy a Snack [Bamert, Decker, Elsen, W, Welten, 2013]

110 Transaction Confidence

111 Transaction Confidence TX confidence(tx ) =

112 Transaction Confidence TX confidence(tx ) =

113 Transaction Confidence confidence(tx ) =

114 Transaction Confidence confidence(tx ) =

115 Doublespend Detection 1.0 Doublespend detection 0.8 Detection probability Node sample size [Bamert, Decker, Elsen, W, Welten, 2013]

116 Time to Detection Time until detection Average time Median time 95 percentile 99 percentile Time [s] Node sample size [Bamert, Decker, Elsen, W, Welten, 2013]

117 Successful Doublespend Probability Probability of successful double spend Node sample size [Bamert, Decker, Elsen, W, Welten, 2013]

118 Successful Doublespend Probability Probability of successful double spend 0.088% Node sample size [Bamert, Decker, Elsen, W, Welten, 2013]