Added selfish mining

pow_research/selfish_mining.py

@@ -0,0 +1,54 @@
+import random
+# Attacker percent of hashpower
+alpha = 0.333
+# Probability attacker can win in a network race
+gamma = 0.0
+
+# Total blocks of attacker and honest miners
+attacker_blocks = 0
+honest_blocks = 0
+# At the start of each outer loop, the attacker and honest
+# chains are fully shared
+while attacker_blocks + honest_blocks < 100000:
+    # 1-alpha: honest miner makes block, attacker accepts
+    if random.random() > alpha:
+        honest_blocks += 1
+        continue
+    # alpha: attacker makes block
+
+    # 1-alpha: honest miners publish a block and catch up
+    # Attacker publishes their block. They now have two
+    # chances to win: (i) they make the next block, (ii)
+    # the next block is made by an honest miner who saw
+    # the attacker's block first
+    if random.random() > alpha:
+        # Alpha: attacker mines next block, publishes both blocks
+        if random.random() < alpha:
+            attacker_blocks += 2
+            continue
+        # 1-alpha: honest miners mine next block, publish
+        # gamma: that honest miner saw the attacker's block first,
+        # so the new winning chain contains one honest block and
+        # one attacker block
+        if random.random() < gamma:
+            honest_blocks += 1
+            attacker_blocks += 1
+        # 1-gamma: that honest miner saw the honest block first,
+        # so the winning chain contains two honest blocks
+        else:
+            honest_blocks += 2
+        continue
+    # alpha: attacker is now two blocks ahead
+    state = [2, 0]
+
+    # Keep going until attacker only one block ahead
+    while state[0] - state[1] > 1:
+        if random.random() > alpha:
+            state[1] += 1
+        else:
+            state[0] += 1
+    # Attacker publishes, overtakes honest chain
+    attacker_blocks += state[0]
+
+print("Attacker blocks percentage: %.3f" %
+      (attacker_blocks / (attacker_blocks + honest_blocks) * 100))