Python實(shí)現(xiàn)類似比特幣的加密貨幣區(qū)塊鏈的創(chuàng)建與交易實(shí)例

更新時間：2018年03月20日 12:08:40 投稿：wdc

本文講解了Python實(shí)現(xiàn)類似比特幣的加密貨幣區(qū)塊鏈的創(chuàng)建與交易實(shí)例方法

雖然有些人認(rèn)為區(qū)塊鏈?zhǔn)且粋€早晚會出現(xiàn)問題的解決方案，但是毫無疑問，這個創(chuàng)新技術(shù)是一個計(jì)算機(jī)技術(shù)上的奇跡。那么，究竟什么是區(qū)塊鏈呢？

區(qū)塊鏈

以比特幣（Bitcoin）或其它加密貨幣按時間順序公開地記錄交易的數(shù)字賬本。

更通俗的說，它是一個公開的數(shù)據(jù)庫，新的數(shù)據(jù)存儲在被稱之為區(qū)塊（block）的容器中，并被添加到一個不可變的鏈（chain）中（因此被稱為區(qū)塊鏈（blockchain）），之前添加的數(shù)據(jù)也在該鏈中。對于比特幣或其它加密貨幣來說，這些數(shù)據(jù)就是一組組交易，不過，也可以是其它任何類型的數(shù)據(jù)。

區(qū)塊鏈技術(shù)帶來了全新的、完全數(shù)字化的貨幣，如比特幣和萊特幣（Litecoin），它們并不由任何中心機(jī)構(gòu)管理。這給那些認(rèn)為當(dāng)今的銀行系統(tǒng)是騙局并將最終走向失敗的人帶來了自由。區(qū)塊鏈也革命性地改變了分布式計(jì)算的技術(shù)形式，如以太坊（Ethereum）就引入了一種有趣的概念：智能合約（smart contract）。

在這篇文章中，我將用不到 50 行的 Python 2.x 代碼實(shí)現(xiàn)一個簡單的區(qū)塊鏈，我把它叫做 SnakeCoin。

不到 50 行代碼的區(qū)塊鏈

我們首先將從定義我們的區(qū)塊是什么開始。在區(qū)塊鏈中，每個區(qū)塊隨同時間戳及可選的索引一同存儲。在 SnakeCoin 中，我們會存儲這兩者。為了確保整個區(qū)塊鏈的完整性，每個區(qū)塊都會有一個自識別的哈希值。如在比特幣中，每個區(qū)塊的哈希是該塊的索引、時間戳、數(shù)據(jù)和前一個區(qū)塊的哈希值等數(shù)據(jù)的加密哈希值。這里提及的“數(shù)據(jù)”可以是任何你想要的數(shù)據(jù)。

import hashlib as hasher

class Block:
 def __init__(self, index, timestamp, data, previous_hash):
  self.index = index
  self.timestamp = timestamp
  self.data = data
  self.previous_hash = previous_hash
  self.hash = self.hash_block()
 
 def hash_block(self):
  sha = hasher.sha256()
  sha.update(str(self.index) + 
        str(self.timestamp) + 
        str(self.data) + 
        str(self.previous_hash))
  return sha.hexdigest()

import hashlib as hasher
 
class Block:
 def __init__(self, index, timestamp, data, previous_hash):
  self.index = index
  self.timestamp = timestamp
  self.data = data
  self.previous_hash = previous_hash
  self.hash = self.hash_block()
 
 def hash_block(self):
  sha = hasher.sha256()
  sha.update(str(self.index) + 
        str(self.timestamp) + 
        str(self.data) + 
        str(self.previous_hash))
  return sha.hexdigest()

現(xiàn)在我們有了區(qū)塊的結(jié)構(gòu)了，不過我們需要創(chuàng)建的是一個區(qū)塊鏈。我們需要把區(qū)塊添加到一個實(shí)際的鏈中。如我們之前提到過的，每個區(qū)塊都需要前一個區(qū)塊的信息。但問題是，該區(qū)塊鏈中的第一個區(qū)塊在哪里？好吧，這個第一個區(qū)塊，也稱之為創(chuàng)世區(qū)塊，是一個特別的區(qū)塊。在很多情況下，它是手工添加的，或通過獨(dú)特的邏輯添加的。

我們將創(chuàng)建一個函數(shù)來簡單地返回一個創(chuàng)世區(qū)塊解決這個問題。這個區(qū)塊的索引為 0 ，其包含一些任意的數(shù)據(jù)值，其“前一哈希值”參數(shù)也是任意值。

import datetime as date

def create_genesis_block():
 # Manually construct a block with
 # index zero and arbitrary previous hash
 return Block(0, date.datetime.now(), "Genesis Block", "0")

import datetime as date
 
def create_genesis_block():
 # Manually construct a block with
 # index zero and arbitrary previous hash
 return Block(0, date.datetime.now(), "Genesis Block", "0")

現(xiàn)在我們可以創(chuàng)建創(chuàng)世區(qū)塊了，我們需要一個函數(shù)來生成該區(qū)塊鏈中的后繼區(qū)塊。該函數(shù)將獲取鏈中的前一個區(qū)塊作為參數(shù)，為要生成的區(qū)塊創(chuàng)建數(shù)據(jù)，并用相應(yīng)的數(shù)據(jù)返回新的區(qū)塊。新的區(qū)塊的哈希值來自于之前的區(qū)塊，這樣每個新的區(qū)塊都提升了該區(qū)塊鏈的完整性。如果我們不這樣做，外部參與者就很容易“改變過去”，把我們的鏈替換為他們的新鏈了。這個哈希鏈起到了加密的證明作用，并有助于確保一旦一個區(qū)塊被添加到鏈中，就不能被替換或移除。

def next_block(last_block):
 this_index = last_block.index + 1
 this_timestamp = date.datetime.now()
 this_data = "Hey! I'm block " + str(this_index)
 this_hash = last_block.hash
 return Block(this_index, this_timestamp, this_data, this_hash)

def next_block(last_block):
 this_index = last_block.index + 1
 this_timestamp = date.datetime.now()
 this_data = "Hey! I'm block " + str(this_index)
 this_hash = last_block.hash
 return Block(this_index, this_timestamp, this_data, this_hash)

這就是主要的部分。

現(xiàn)在我們能創(chuàng)建自己的區(qū)塊鏈了！在這里，這個區(qū)塊鏈?zhǔn)且粋€簡單的 Python 列表。其第一個的元素是我們的創(chuàng)世區(qū)塊，我們會添加后繼區(qū)塊。因?yàn)?SnakeCoin 是一個極小的區(qū)塊鏈，我們僅僅添加了 20 個區(qū)塊。我們通過循環(huán)來完成它。

# Create the blockchain and add the genesis block
blockchain = [create_genesis_block()]
previous_block = blockchain[0]

# How many blocks should we add to the chain
# after the genesis block
num_of_blocks_to_add = 20

# Add blocks to the chain
for i in range(0, num_of_blocks_to_add):
 block_to_add = next_block(previous_block)
 blockchain.append(block_to_add)
 previous_block = block_to_add
 # Tell everyone about it!
 print "Block #{} has been added to the blockchain!".format(block_to_add.index)
 print "Hash: {}n".format(block_to_add.hash)

# Create the blockchain and add the genesis block
blockchain = [create_genesis_block()]
previous_block = blockchain[0]
 
# How many blocks should we add to the chain
# after the genesis block
num_of_blocks_to_add = 20
 
# Add blocks to the chain
for i in range(0, num_of_blocks_to_add):
 block_to_add = next_block(previous_block)
 blockchain.append(block_to_add)
 previous_block = block_to_add
 # Tell everyone about it!
 print "Block #{} has been added to the blockchain!".format(block_to_add.index)
 print "Hash: {}n".format(block_to_add.hash)

讓我們看看我們的成果：

別擔(dān)心，它將一直添加到 20 個區(qū)塊

很好，我們的區(qū)塊鏈可以工作了。如果你想要在主控臺查看更多的信息，你可以編輯其完整的源代碼并輸出每個區(qū)塊的時間戳或數(shù)據(jù)。

這就是 SnakeCoin 所具有的功能。要使 SnakeCoin 達(dá)到現(xiàn)今的產(chǎn)品級的區(qū)塊鏈的高度，我們需要添加更多的功能，如服務(wù)器層，以在多臺機(jī)器上跟蹤鏈的改變，并通過工作量證明算法（POW）來限制給定時間周期內(nèi)可以添加的區(qū)塊數(shù)量。

如果你想了解更多技術(shù)細(xì)節(jié)，你可以在這里查看最初的比特幣白皮書。

讓這個極小區(qū)塊鏈稍微變大些
這個極小的區(qū)塊鏈及其簡單，自然也相對容易完成。但是因其簡單也帶來了一些缺陷。首先，SnakeCoin 僅能運(yùn)行在單一的一臺機(jī)器上，所以它相距分布式甚遠(yuǎn)，更別提去中心化了。其次，區(qū)塊添加到區(qū)塊鏈中的速度同在主機(jī)上創(chuàng)建一個 Python 對象并添加到列表中一樣快。在我們的這個簡單的區(qū)塊鏈中，這不是問題，但是如果我們想讓 SnakeCoin 成為一個實(shí)際的加密貨幣，我們就需要控制在給定時間內(nèi)能創(chuàng)建的區(qū)塊（和幣）的數(shù)量。

從現(xiàn)在開始，SnakeCoin 中的“數(shù)據(jù)”將是交易數(shù)據(jù)，每個區(qū)塊的“數(shù)據(jù)”字段都將是一些交易信息的列表。接著我們來定義“交易”。每個“交易”是一個 JSON 對象，其記錄了幣的發(fā)送者、接收者和轉(zhuǎn)移的 SnakeCoin 數(shù)量。注：交易信息是 JSON 格式，原因我很快就會說明。

{
 "from": "71238uqirbfh894-random-public-key-a-alkjdflakjfewn204ij",
 "to": "93j4ivnqiopvh43-random-public-key-b-qjrgvnoeirbnferinfo",
 "amount": 3
}


{
 "from": "71238uqirbfh894-random-public-key-a-alkjdflakjfewn204ij",
 "to": "93j4ivnqiopvh43-random-public-key-b-qjrgvnoeirbnferinfo",
 "amount": 3
}

現(xiàn)在我們知道了交易信息看起來的樣子了，我們需要一個辦法來將其加到我們的區(qū)塊鏈網(wǎng)絡(luò)中的一臺計(jì)算機(jī)（稱之為節(jié)點(diǎn)）中。要做這個事情，我們會創(chuàng)建一個簡單的 HTTP 服務(wù)器，以便每個用戶都可以讓我們的節(jié)點(diǎn)知道發(fā)生了新的交易。節(jié)點(diǎn)可以接受 POST 請求，請求數(shù)據(jù)為如上的交易信息。這就是為什么交易信息是 JSON 格式的：我們需要它們可以放在請求信息中傳遞給服務(wù)器。

$ pip install flask # 首先安裝 Web 服務(wù)器框架
1
$ pip install flask # 首先安裝 Web 服務(wù)器框架
Python

from flask import Flask
from flask import request
node = Flask(__name__)
# Store the transactions that
# this node has in a list
this_nodes_transactions = []
@node.route('/txion', methods=['POST'])
def transaction():
 if request.method == 'POST':
  # On each new POST request,
  # we extract the transaction data
  new_txion = request.get_json()
  # Then we add the transaction to our list
  this_nodes_transactions.append(new_txion)
  # Because the transaction was successfully
  # submitted, we log it to our console
  print "New transaction"
  print "FROM: {}".format(new_txion['from'])
  print "TO: {}".format(new_txion['to'])
  print "AMOUNT: {}\n".format(new_txion['amount'])
  # Then we let the client know it worked out
  return "Transaction submission successful\n"
node.run()

from flask import Flask
from flask import request
node = Flask(__name__)
# Store the transactions that
# this node has in a list
this_nodes_transactions = []
@node.route('/txion', methods=['POST'])
def transaction():
 if request.method == 'POST':
  # On each new POST request,
  # we extract the transaction data
  new_txion = request.get_json()
  # Then we add the transaction to our list
  this_nodes_transactions.append(new_txion)
  # Because the transaction was successfully
  # submitted, we log it to our console
  print "New transaction"
  print "FROM: {}".format(new_txion['from'])
  print "TO: {}".format(new_txion['to'])
  print "AMOUNT: {}\n".format(new_txion['amount'])
  # Then we let the client know it worked out
  return "Transaction submission successful\n"
node.run()

現(xiàn)在我們有了一種保存用戶彼此發(fā)送 SnakeCoin 的記錄的方式。這就是為什么人們將區(qū)塊鏈稱之為公共的、分布式賬本：所有的交易信息存儲給所有人看，并被存儲在該網(wǎng)絡(luò)的每個節(jié)點(diǎn)上。

但是，有個問題：人們從哪里得到 SnakeCoin 呢？現(xiàn)在還沒有辦法得到，還沒有一個稱之為 SnakeCoin 這樣的東西，因?yàn)槲覀冞€沒有創(chuàng)建和分發(fā)任何一個幣。要創(chuàng)建新的幣，人們需要“挖”一個新的 SnakeCoin 區(qū)塊。當(dāng)他們成功地挖到了新區(qū)塊，就會創(chuàng)建出一個新的 SnakeCoin ，并獎勵給挖出該區(qū)塊的人（礦工）。一旦挖礦的礦工將 SnakeCoin 發(fā)送給別人，這個幣就流通起來了。

我們不想讓挖新的 SnakeCoin 區(qū)塊太容易，因?yàn)檫@將導(dǎo)致 SnakeCoin 太多了，其價(jià)值就變低了；同樣，我們也不想讓它變得太難，因?yàn)槿绻麤]有足夠的幣供每個人使用，它們對于我們來說就太昂貴了。為了控制挖新的 SnakeCoin 區(qū)塊的難度，我們會實(shí)現(xiàn)一個工作量證明（Proof-of-Work）（PoW）算法。工作量證明基本上就是一個生成某個項(xiàng)目比較難，但是容易驗(yàn)證（其正確性）的算法。這個項(xiàng)目被稱之為“證明”，聽起來就像是它證明了計(jì)算機(jī)執(zhí)行了特定的工作量。

在 SnakeCoin 中，我們創(chuàng)建了一個簡單的 PoW 算法。要創(chuàng)建一個新區(qū)塊，礦工的計(jì)算機(jī)需要遞增一個數(shù)字，當(dāng)該數(shù)字能被 9 （“SnakeCoin” 這個單詞的字母數(shù)）整除時，這就是最后這個區(qū)塊的證明數(shù)字，就會挖出一個新的 SnakeCoin 區(qū)塊，而該礦工就會得到一個新的 SnakeCoin。

# ...blockchain
# ...Block class definition
miner_address = "q3nf394hjg-random-miner-address-34nf3i4nflkn3oi"
def proof_of_work(last_proof):
 # Create a variable that we will use to find
 # our next proof of work
 incrementor = last_proof + 1
 # Keep incrementing the incrementor until
 # it's equal to a number divisible by 9
 # and the proof of work of the previous
 # block in the chain
 while not (incrementor % 9 == 0 and incrementor % last_proof == 0):
  incrementor += 1
 # Once that number is found,
 # we can return it as a proof
 # of our work
 return incrementor
@node.route('/mine', methods = ['GET'])
def mine():
 # Get the last proof of work
 last_block = blockchain[len(blockchain) - 1]
 last_proof = last_block.data['proof-of-work']
 # Find the proof of work for
 # the current block being mined
 # Note: The program will hang here until a new
 #    proof of work is found
 proof = proof_of_work(last_proof)
 # Once we find a valid proof of work,
 # we know we can mine a block so 
 # we reward the miner by adding a transaction
 this_nodes_transactions.append(
  { "from": "network", "to": miner_address, "amount": 1 }
 )
 # Now we can gather the data needed
 # to create the new block
 new_block_data = {
  "proof-of-work": proof,
  "transactions": list(this_nodes_transactions)
 }
 new_block_index = last_block.index + 1
 new_block_timestamp = this_timestamp = date.datetime.now()
 last_block_hash = last_block.hash
 # Empty transaction list
 this_nodes_transactions[:] = []
 # Now create the
 # new block!
 mined_block = Block(
  new_block_index,
  new_block_timestamp,
  new_block_data,
  last_block_hash
 )
 blockchain.append(mined_block)
 # Let the client know we mined a block
 return json.dumps({
   "index": new_block_index,
   "timestamp": str(new_block_timestamp),
   "data": new_block_data,
   "hash": last_block_hash
 }) + "\n"

# ...blockchain
# ...Block class definition
miner_address = "q3nf394hjg-random-miner-address-34nf3i4nflkn3oi"
def proof_of_work(last_proof):
 # Create a variable that we will use to find
 # our next proof of work
 incrementor = last_proof + 1
 # Keep incrementing the incrementor until
 # it's equal to a number divisible by 9
 # and the proof of work of the previous
 # block in the chain
 while not (incrementor % 9 == 0 and incrementor % last_proof == 0):
  incrementor += 1
 # Once that number is found,
 # we can return it as a proof
 # of our work
 return incrementor
@node.route('/mine', methods = ['GET'])
def mine():
 # Get the last proof of work
 last_block = blockchain[len(blockchain) - 1]
 last_proof = last_block.data['proof-of-work']
 # Find the proof of work for
 # the current block being mined
 # Note: The program will hang here until a new
 #    proof of work is found
 proof = proof_of_work(last_proof)
 # Once we find a valid proof of work,
 # we know we can mine a block so 
 # we reward the miner by adding a transaction
 this_nodes_transactions.append(
  { "from": "network", "to": miner_address, "amount": 1 }
 )
 # Now we can gather the data needed
 # to create the new block
 new_block_data = {
  "proof-of-work": proof,
  "transactions": list(this_nodes_transactions)
 }
 new_block_index = last_block.index + 1
 new_block_timestamp = this_timestamp = date.datetime.now()
 last_block_hash = last_block.hash
 # Empty transaction list
 this_nodes_transactions[:] = []
 # Now create the
 # new block!
 mined_block = Block(
  new_block_index,
  new_block_timestamp,
  new_block_data,
  last_block_hash
 )
 blockchain.append(mined_block)
 # Let the client know we mined a block
 return json.dumps({
   "index": new_block_index,
   "timestamp": str(new_block_timestamp),
   "data": new_block_data,
   "hash": last_block_hash
 }) + "\n"

現(xiàn)在，我們能控制特定的時間段內(nèi)挖到的區(qū)塊數(shù)量，并且我們給了網(wǎng)絡(luò)中的人新的幣，讓他們彼此發(fā)送。但是如我們說的，我們只是在一臺計(jì)算機(jī)上做的。如果區(qū)塊鏈?zhǔn)侨ブ行幕模覀冊鯓硬拍艽_保每個節(jié)點(diǎn)都有相同的鏈呢？要做到這一點(diǎn)，我們會使每個節(jié)點(diǎn)都廣播其（保存的）鏈的版本，并允許它們接受其它節(jié)點(diǎn)的鏈。然后，每個節(jié)點(diǎn)會校驗(yàn)其它節(jié)點(diǎn)的鏈，以便網(wǎng)絡(luò)中每個節(jié)點(diǎn)都能夠達(dá)成最終的鏈的共識。這稱之為共識算法（consensus algorithm）。

我們的共識算法很簡單：如果一個節(jié)點(diǎn)的鏈與其它的節(jié)點(diǎn)的不同（例如有沖突），那么最長的鏈保留，更短的鏈會被刪除。如果我們網(wǎng)絡(luò)上的鏈沒有了沖突，那么就可以繼續(xù)了。

@node.route('/blocks', methods=['GET'])
def get_blocks():
 chain_to_send = blockchain
 # Convert our blocks into dictionaries
 # so we can send them as json objects later
 for block in chain_to_send:
  block_index = str(block.index)
  block_timestamp = str(block.timestamp)
  block_data = str(block.data)
  block_hash = block.hash
  block = {
   "index": block_index,
   "timestamp": block_timestamp,
   "data": block_data,
   "hash": block_hash
  }
 # Send our chain to whomever requested it
 chain_to_send = json.dumps(chain_to_send)
 return chain_to_send
def find_new_chains():
 # Get the blockchains of every
 # other node
 other_chains = []
 for node_url in peer_nodes:
  # Get their chains using a GET request
  block = requests.get(node_url + "/blocks").content
  # Convert the JSON object to a Python dictionary
  block = json.loads(block)
  # Add it to our list
  other_chains.append(block)
 return other_chains
def consensus():
 # Get the blocks from other nodes
 other_chains = find_new_chains()
 # If our chain isn't longest,
 # then we store the longest chain
 longest_chain = blockchain
 for chain in other_chains:
  if len(longest_chain) < len(chain):
   longest_chain = chain
 # If the longest chain wasn't ours,
 # then we set our chain to the longest
 blockchain = longest_chain

@node.route('/blocks', methods=['GET'])
def get_blocks():
 chain_to_send = blockchain
 # Convert our blocks into dictionaries
 # so we can send them as json objects later
 for block in chain_to_send:
  block_index = str(block.index)
  block_timestamp = str(block.timestamp)
  block_data = str(block.data)
  block_hash = block.hash
  block = {
   "index": block_index,
   "timestamp": block_timestamp,
   "data": block_data,
   "hash": block_hash
  }
 # Send our chain to whomever requested it
 chain_to_send = json.dumps(chain_to_send)
 return chain_to_send
def find_new_chains():
 # Get the blockchains of every
 # other node
 other_chains = []
 for node_url in peer_nodes:
  # Get their chains using a GET request
  block = requests.get(node_url + "/blocks").content
  # Convert the JSON object to a Python dictionary
  block = json.loads(block)
  # Add it to our list
  other_chains.append(block)
 return other_chains
def consensus():
 # Get the blocks from other nodes
 other_chains = find_new_chains()
 # If our chain isn't longest,
 # then we store the longest chain
 longest_chain = blockchain
 for chain in other_chains:
  if len(longest_chain) < len(chain):
   longest_chain = chain
 # If the longest chain wasn't ours,
 # then we set our chain to the longest
 blockchain = longest_chain

我們差不多就要完成了。在運(yùn)行了完整的 SnakeCoin 服務(wù)器代碼之后，在你的終端可以運(yùn)行如下代碼。（假設(shè)你已經(jīng)安裝了 cCUL）。

1、創(chuàng)建交易

curl "localhost:5000/txion" \
   -H "Content-Type: application/json" \
   -d '{"from": "akjflw", "to":"fjlakdj", "amount": 3}'

curl "localhost:5000/txion" \
   -H "Content-Type: application/json" \
   -d '{"from": "akjflw", "to":"fjlakdj", "amount": 3}'

2、挖一個新區(qū)塊

curl localhost:5000/mine

curl localhost:5000/mine

3、查看結(jié)果。從客戶端窗口，我們可以看到。

對代碼做下美化處理，我們看到挖礦后我們得到的新區(qū)塊的信息：

{
 "index": 2,
 "data": {
  "transactions": [
   {
    "to": "fjlakdj",
    "amount": 3,
    "from": "akjflw"
   },
   {
    "to": "q3nf394hjg-random-miner-address-34nf3i4nflkn3oi",
    "amount": 1,
    "from": "network"
   }
  ],
  "proof-of-work": 36
 },
 "hash": "151edd3ef6af2e7eb8272245cb8ea91b4ecfc3e60af22d8518ef0bba8b4a6b18",
 "timestamp": "2017-07-23 11:23:10.140996"
}

{
 "index": 2,
 "data": {
  "transactions": [
   {
    "to": "fjlakdj",
    "amount": 3,
    "from": "akjflw"
   },
   {
    "to": "q3nf394hjg-random-miner-address-34nf3i4nflkn3oi",
    "amount": 1,
    "from": "network"
   }
  ],
  "proof-of-work": 36
 },
 "hash": "151edd3ef6af2e7eb8272245cb8ea91b4ecfc3e60af22d8518ef0bba8b4a6b18",
 "timestamp": "2017-07-23 11:23:10.140996"
}

大功告成！現(xiàn)在 SnakeCoin 可以運(yùn)行在多個機(jī)器上，從而創(chuàng)建了一個網(wǎng)絡(luò)，而且真實(shí)的 SnakeCoin 也能被挖到了。

你可以根據(jù)你的喜好去修改 SnakeCoin 服務(wù)器代碼，并問各種問題了，好了本文暫時講解一下Python實(shí)現(xiàn)類似比特幣的加密貨幣區(qū)塊鏈的創(chuàng)建與交易實(shí)例。

下一篇我們將討論創(chuàng)建一個 SnakeCoin 錢包，這樣用戶就可以發(fā)送、接收和存儲他們的 SnakeCoin 了

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