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Dummy implementation of a blockchain system with a single miner to display how the mining process works
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import time | |
from collections import Counter | |
from dataclasses import dataclass, field | |
from hashlib import sha512 | |
from typing import List | |
import matplotlib.pyplot as plt | |
import numpy as np | |
from tqdm import trange | |
@dataclass(frozen=False) | |
class Block: | |
previous_block_hash: bytes | |
messages: tuple | |
nonce: int | |
time: int | |
target_difficulty: int | |
@dataclass(frozen=True) | |
class FrozenBlock: | |
previous_block_hash: bytes | |
messages: tuple | |
nonce: int | |
time: int | |
target_difficulty: int | |
@dataclass(frozen=True) | |
class BlockchainSystem: | |
block_time: float = 6 | |
adaptive_difficulty_interval: int = 10 | |
block_time_sensitivity: float = .10 | |
genesis: FrozenBlock = field(default_factory=lambda: FrozenBlock( | |
previous_block_hash=bytes(0), | |
messages=tuple(), | |
nonce=0, | |
time=int(time.time()), | |
target_difficulty=0 | |
)) | |
class Miner: | |
def __init__(self, system: BlockchainSystem): | |
self.blockchain: List[FrozenBlock] = [system.genesis] | |
self.system: BlockchainSystem = system | |
self.queue: List[str] = [] | |
@property | |
def last_block(self): | |
return self.blockchain[-1] | |
def receive(self, message: str): | |
self.queue.append(message) | |
@staticmethod | |
def hash(block): | |
m = sha512() | |
m.update( | |
f"{block.previous_block_hash}{block.nonce}{block.messages}{block.time}{block.target_difficulty}".encode()) | |
return m.digest()[:10] | |
def compute_difficulty(self): | |
if len(self.blockchain) % self.system.adaptive_difficulty_interval > 0: | |
return self.last_block.target_difficulty | |
few_last_times = [b.time for b in self.blockchain[-self.system.adaptive_difficulty_interval:]] | |
duration_avg = np.ediff1d(few_last_times + [int(time.time())]).mean() | |
ref = self.system.block_time | |
if np.isclose(duration_avg, ref, rtol=self.system.block_time_sensitivity): | |
return self.last_block.target_difficulty | |
elif duration_avg < ref: | |
diff = (ref - duration_avg) / ref | |
dist = round(diff / self.system.block_time_sensitivity) | |
return self.last_block.target_difficulty + dist | |
else: | |
diff = (duration_avg - ref) / ref | |
dist = round(diff / self.system.block_time_sensitivity) | |
return self.last_block.target_difficulty - dist | |
def select(self): | |
return Block( | |
previous_block_hash=self.hash(self.last_block), | |
messages=tuple(self.queue), | |
nonce=0, | |
time=int(time.time()), | |
target_difficulty=self.compute_difficulty()) | |
def is_mined(self, block): | |
""" | |
A block is mined if its hash starts with a selection of numeric characters. | |
The number of concerned characters, and the selection of numeric characters depends on the difficulty. | |
n | n = self.target_difficulty // 256 | |
e | e = 256 - self.target_difficulty % 256 | |
The n first characters must be the byte 0 | |
The n + 1 character must be a byte up to e (excluded). | |
""" | |
h = self.hash(block) | |
max_difficulty_chars = block.target_difficulty // 256 | |
if not all(b == 0 for b in h[:max_difficulty_chars]): | |
return False | |
complement_difficulty = 256 - block.target_difficulty % 256 | |
return h[max_difficulty_chars] < complement_difficulty | |
def mine(self, block): | |
while not self.is_mined(block): | |
block.nonce += 1 | |
self.queue = [] | |
self.blockchain.append(FrozenBlock(**vars(block))) | |
def main(): | |
system = BlockchainSystem() | |
m = Miner(system) | |
print('searching stationary state') | |
for _ in trange(1000): | |
block = m.select() | |
m.mine(block) | |
print('simulating under stationary state') | |
for _ in trange(1000): | |
block = m.select() | |
m.mine(block) | |
difficulties = [b.target_difficulty for b in m.blockchain[1000:]] | |
print(np.mean(difficulties), np.median(difficulties)) | |
counter = Counter(difficulties) | |
block_times = [b.time for b in m.blockchain[1000:]] | |
durations = np.ediff1d(block_times) | |
print(np.mean(durations), np.median(durations)) | |
fig, (ax1, ax2) = plt.subplots(ncols=2) | |
ax1.set(xlabel="Difficulty", ylabel="Block count", | |
title="Difficulty") | |
ax2.set(xlabel="Block time", | |
title="Block time") | |
ax1.hist(difficulties, bins=len(counter)) | |
ax2.hist(durations, bins=50) | |
plt.show() | |
if __name__ == '__main__': | |
main() |
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