From 13a30dedf47a3a6c15c1d7b3ebee768bc3011dc4 Mon Sep 17 00:00:00 2001
From: Vitalik Buterin <v@buterin.com>
Date: Tue, 31 Jul 2018 19:15:02 -0400
Subject: [PATCH] Added simulation of 99% fault tolerant synchronous consensus

---
 99fault/consensus.py    | 89 +++++++++++++++++++++++++++++++++++++++++
 clock_disparity/test.py |  4 +-
 2 files changed, 91 insertions(+), 2 deletions(-)
 create mode 100644 99fault/consensus.py

diff --git a/99fault/consensus.py b/99fault/consensus.py
new file mode 100644
index 0000000..c30b45d
--- /dev/null
+++ b/99fault/consensus.py
@@ -0,0 +1,89 @@
+# Implementation of 99% fault tolerant consensus as decribed by Leslie Lamport
+# on page 391 of https://people.eecs.berkeley.edu/~luca/cs174/byzantine.pdf
+
+import random
+
+TIMEOUT = 10
+LATENCY = 5
+
+# Network simulator
+class Network():
+    def __init__(self):
+        self.queue = {}
+        self.time = 0
+
+    def add_node(self, node):
+        self.queue[node.id] = {-1: node}
+
+    def broadcast(self, msg, at=0):
+        for q in self.queue.keys():
+            self.send_to(msg, q, at)
+
+    def send_to(self, msg, id, at):
+        q = self.queue[id]
+        newtime = max(self.time, at) + random.randrange(LATENCY * 2 - 1) + 1
+        if newtime not in q:
+            q[newtime] = []
+        q[newtime].append(msg)
+
+    def tick(self):
+        self.time += 1
+        for q in self.queue.values():
+            if self.time in q:
+                for msg in q[self.time]:
+                    q[-1].on_receive(msg)
+
+# A node in the network (not including the "commander")
+class Node():
+
+    def __init__(self, network, id, honest=True):
+        self.seen = {}
+        self.id = id
+        self.network = network
+        self.network.add_node(self)
+        self.honest = honest
+
+    # Upon receiving a message...
+    def on_receive(self, msg):
+        if self.id == 0 and len(msg) == 1:
+            print('Seen', msg[0], self.network.time, 'already seen', sorted(self.seen.keys()))
+        # Only proceed if v not in V_i...
+        # Byzantine nodes ignore this rule 5% of the time
+        if (msg[0] in self.seen) and (self.honest or random.random() < 0.95):
+            return
+        # Timeout logic (see page 399)
+        # Byzantine nodes ignore this rule
+        if (len(msg) * TIMEOUT < self.network.time) and self.honest:
+            return
+        self.seen[msg[0]] = True
+        new_msg = msg + [self.id]
+        # Broadcast v:0:j1...jk:i
+        # Byzantine nodes delay broadcast to split honest receiving nodes by timeout
+        self.network.broadcast(new_msg, at=self.network.time if self.honest else self.network.time + int(TIMEOUT / 1.5))
+
+    def choice(self):
+        return max(self.seen.keys())
+
+def test():
+    n = Network()
+    nodes = [Node(n, i, i%4==0) for i in range(20)]
+    for i in range(30):
+        for _ in range(2):
+            z = random.randrange(20)
+            n.send_to([1000 + i], z, at=5+i*2)
+    for i in range(21 * LATENCY):
+        n.tick()
+        if i % 10 == 0:
+            print("Value sets", [sorted(node.seen.keys()) for node in nodes])
+    countz = {}
+    maxval = ""
+    for node in nodes:
+        if node.honest:
+            k = str(sorted(node.seen.keys()))
+            countz[k] = countz.get(k, 0) + 1
+            if countz[k] > countz.get(maxval, 0):
+                maxval = k
+    print("Most popular: %s" % maxval, "with %d agreeing" % countz[maxval])
+
+if __name__ == '__main__':
+    test()
diff --git a/clock_disparity/test.py b/clock_disparity/test.py
index 445ba05..0e9d1e6 100644
--- a/clock_disparity/test.py
+++ b/clock_disparity/test.py
@@ -2,8 +2,8 @@ from networksim import NetworkSimulator
 from ghost_node import Node, NOTARIES, Block, genesis
 from distributions import normal_distribution
 
-net = NetworkSimulator(latency=12)
-notaries = [Node(i, net, ts=max(normal_distribution(200, 200)(), 0) * 0.1, sleepy=i%4==0) for i in range(NOTARIES)]
+net = NetworkSimulator(latency=22)
+notaries = [Node(i, net, ts=max(normal_distribution(300, 300)(), 0) * 0.1, sleepy=i%4==0) for i in range(NOTARIES)]
 net.agents = notaries
 net.generate_peers()
 for i in range(100000):