Added randao analysis

randao_analysis/paths.py

@@ -0,0 +1,141 @@
+import random
+from heapq import heappush, heappop, heapify
+
+LATENCY = 1
+SKIP = 6
+
+# The score of a node in the search graph, for A* search
+def score_node(n):
+    time, height = n
+    return time - height * (LATENCY + 0.0000001)
+
+# `alpha`: percentage of the network controlled by the actor
+# `max_height`: stop at this height
+# Searches for the shortest path (in terms of time) to
+# reach any particular height, and builds up an array
+# `outputs`, mapping height => min time needed to reach that
+# height
+def search(alpha, max_height):
+    # Nodes are of the form (time, height)
+    first_node = (0, 0)
+    best_score = score_node(first_node)
+    # The heap of nodes in the search graph (ie. blocks)
+    nodes = [(best_score, first_node)]
+    # Minimum time needed to reach a given height
+    outputs = [0]
+    # For efficiency reasons, create a random list of delays,
+    # instead of recalculating these every time
+    delays = []
+    for i in range(200):
+        o = [LATENCY]
+        for _ in range(3):
+            while random.random() > alpha:
+                o[-1] += SKIP
+            o.append(o[-1])
+        delays.append(o)
+
+    while len(nodes):
+        # Process the most favorable not-yet-processed node
+        score, (time, height) = heappop(nodes)
+        # If this is the first time we've processed a node
+        # with this height...
+        if height > len(outputs):
+            outputs.append(time)
+            # Check if we should exit
+            if height >= max_height:
+                return outputs
+        # Add a maximum of 3 children to this node
+        for v in random.choice(delays):
+            newnode = (time + v, height + 1)
+            heappush(nodes, (score_node(newnode), newnode))
+        # For efficiency: cap the heap size at 500-1000
+        if len(nodes) > 1000:
+            nodes = nodes[:500]
+
+# Generate an array, height => time when an honest
+# chain reaches that height
+def honest_chain(alpha, maxheight):
+    outputs = [0]
+    for i in range(maxheight):
+        t = outputs[-1]
+        t += LATENCY
+        while random.random() > alpha:
+            t += SKIP
+        outputs.append(t)
+    return outputs
+
+# Gets the height => time array for honest and
+# attacking party, and returns the highest lead
+# that the attacker gets over the honest party
+def get_attacker_lead(honest, attacker):
+    maxlead = -1
+    for i in range(len(honest)):
+        for j in range(i + maxlead + 1, len(attacker)):
+            if attacker[j] < honest[i]:
+                maxlead = j-i
+            else:
+                break
+    return maxlead + 1
+
+# Attempts a race between the attacker and honest chain.
+# `attacker` = attacker share of network
+# `honest` = honest share of network
+# `maxheight` = give up here
+# Returns the max lead that the attacker gets;
+# alternatively this could be interpreted as the max
+# handicap the attacker could overcome
+def race(attacker, honest, maxheight):
+    h = honest_chain(honest, maxheight)
+    a = search(attacker, maxheight)
+    return get_attacker_lead(h, a)
+
+# Probability that an attacker will win in a standard PoW-style model
+def standard_race_prob(attacker, honest, handicap):
+    # Explanation for this formula is that it's the unique (sensible)
+    # solution to the infinite system of equations that defines it:
+    #
+    # P(a, h, k) = a/(a+h) * P(a, h, k-1) + h/(a+h) * P(a, h, k+1)
+    #
+    # For all k (there's also the boundary condition P(a, h, 0) = 1)
+    #
+    # This equation arises because from any given state, there's a
+    # a/(a+h) chance the attacker makes the next block, and a 
+    # h/(a+h) chance the honest nodes make the next block. To see how
+    # the formula below solves this, let the result for handicap=k be
+    # N; note the result for k+1 is N*a/h, and for k-1 is N*h/a. Now:
+    # 
+    # N = a/(a+h) * N*h/a + h/(a+h) * N*a/h
+    # 1 = a/(a+h) * h/a + h/(a+h) * a/h
+    # 1 = h/(a+h) + a/(a+h)
+
+    return (attacker / honest) ** handicap
+
+# The percentage that would be required to get a given success rate
+# with a given handicap
+def standard_race_equiv_rate(probability, handicap):
+    y = probability ** (1/handicap)
+    return y/(1+y)
+
+def test():
+    # Assume attacker has (0.40, 0.38, 0.36, 0.34, 0.32, 0.30, 0.28); check race probs for handicap 1-8
+    print("Basic tests\n")
+    for alpha in (0.40, 0.38, 0.36, 0.34, 0.32, 0.30, 0.28):
+        race_results = [race(alpha, 1-alpha, 100) for j in range(100)]
+        probs = []
+        for i in range(1, 9):
+            probs.append(len([x for x in race_results if x >= i]) / 100)
+        print("Probs at %.2f: %r" % (alpha, probs))
+        print("Standard race equiv rate: %r" % [standard_race_equiv_rate(x, i+1) for i, x in enumerate(probs)])
+    # Now, try the version where each block requires notarizations from an extra two validators. Here,
+    # if either side has share p, they effectively "really" have share p**3
+    print("\nRequiring 2/2 notarization\n")
+    for alpha in (0.45, 0.44, 0.43, 0.42, 0.41, 0.40, 0.39):
+        race_results = [race(alpha ** 3, (1-alpha) ** 3, 100) for j in range(100)]
+        probs = []
+        for i in range(1, 9):
+            probs.append(len([x for x in race_results if x >= i]) / 100)
+        print("Probs at %.2f: %r" % (alpha, probs))
+        print("Standard race equiv rate: %r" % [standard_race_equiv_rate(x, i+1) for i, x in enumerate(probs)])
+
+if __name__ == '__main__':
+    test()

sharding_fork_choice_poc/beacon_chain_node.py

@@ -24,8 +24,8 @@ BASE_TS_DIFF = 1
 SKIP_TS_DIFF = 6
 SAMPLE = 9
 MIN_SAMPLE = 5
-POWDIFF = 30 * NOTARIES
+POWDIFF = 50 * NOTARIES
-SHARDS = 4
+SHARDS = 12
 
 def checkpow(work, nonce):
     # Discrete log PoW, lolz