The Science of the Blockchain
Roger Wattenhofer
Contents
1 Introduction
1.1 What are Distributed Systems? . . . . . . . . . . . .
1.2 Book Overview . . . . . . . . . . . . . . . . . . . . .
1
1
2
2 Fault-Tolerance & Paxos
5
2.1 Client/Server . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Paxos . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3 Consensus
3.1 Two Friends . . . . . . . . . . . . . . . . . . . . . . .
3.2 Consensus . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Impossibility of Consensus . . . . . . . . . . . . . . .
3.4 Randomized Consensus . . . . . . . . . . . . . . . .
3.5 Shared Coin . . . . . . . . . . . . . . . . . . . . . . .
17
17
18
18
25
29
4 Byzantine Agreement
4.1 Validity . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 How Many Byzantine Nodes? . . . . . . . . . . . . .
4.3 The King Algorithm . . . . . . . . . . . . . . . . . .
4.4 Lower Bound on Number of Rounds . . . . . . . . .
4.5 Asynchronous Byzantine Agreement . . . . . . . . .
33
34
35
38
40
40
5 Authenticated Agreement
45
5.1 Agreement with Authentication . . . . . . . . . . . . 45
5.2 Zyzzyva . . . . . . . . . . . . . . . . . . . . . . . . . 47
6 Quorum Systems
6.1 Load and Work . . . . . . . . . . . . . . . . . . . . .
6.2 Grid Quorum Systems . . . . . . . . . . . . . . . . .
6.3 Fault Tolerance . . . . . . . . . . . . . . . . . . . . .
6.4 Byzantine Quorum Systems . . . . . . . . . . . . . .
v
61
62
64
66
70
vi
CONTENTS
7 Eventual Consistency & Bitcoin
7.1 Consistency, Availability and Partitions . . . . . . .
7.2 Bitcoin . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3 Smart Contracts . . . . . . . . . . . . . . . . . . . .
7.4 Weak Consistency . . . . . . . . . . . . . . . . . . .
77
78
79
87
91
8 Distributed Storage
95
8.1 Consistent Hashing . . . . . . . . . . . . . . . . . . . 95
8.2 Hypercubic Networks . . . . . . . . . . . . . . . . . . 97
8.3 DHT & Churn . . . . . . . . . . . . . . . . . . . . . 105