目录

背景

比特币从诞生到现在已经10年了,最近一段时间因为工作原因接触到了区块链相关的技术,为了揭开其背后的神秘面纱,我们就从头开始构建一个简单的区块链。在行动之前我们先看一下比特币的整体结构.

比特币内部结构

可以看到比特币主要有四个部分

previous hash(前一个区块的hash)

merkle root(默克尔树根节点,内部存储交易数据)

timestamp(当前区块生成的时间)

nonce(旷工计算hash值次数)

transaction_structure.png

我们实现的区块链数据结构(简单实现并不完整)

index 当前第几个区块

timestamp 该区块创建时的时间戳

data 交易信息

previousHash 前一个区块的hash

hash 当前区块的hash

注意点

第一个区块叫做创世区块(genesis block),区块链创建的时候默认生产的

这里用的是单纯的链表,不是用默克尔树存储

coding

from hashlib import sha256

//区块schema

class Block:

def __init__(self,index,timestamp,data,previousHash=""):

self.index = index

self.timestamp = timestamp

self.data = data

self.previousHash = previousHash

self.hash = self.calculateHash()

//计算当前区块的hash值

def calculateHash(self):

plainData = str(self.index)+str(self.timestamp)+str(self.data)

return sha256(plainData.encode('utf-8')).hexdigest()

def __str__(self):

return str(self.__dict__)

//区块链schema

class BlockChain:

//初始化的时候 创建 创世区块

def __init__(self):

self.chain = [self.createGenesisBlock()]

//构建创世区块

def createGenesisBlock(self):

return Block(0,"01/01/2018","genesis block","0")

//获取最后一个区块

def getLatestBlock(self):

return self.chain[len(self.chain)-1]

//往区块链里面添加区块

def addBlock(self,newBlock):

newBlock.previousHash = self.getLatestBlock().hash

newBlock.hash = newBlock.calculateHash()

self.chain.append(newBlock)

def __str__(self):

return str(self.__dict__)

//校验区块链是不是有效的 有没有人被篡改

def chainIsValid(self):

for index in range(1,len(self.chain)):

currentBlock = self.chain[index]

previousBlock = self.chain[index-1]

if (currentBlock.hash != currentBlock.calculateHash()):

return False

if previousBlock.hash != currentBlock.previousHash:

return False

return True

myCoin = BlockChain()

myCoin.addBlock(Block(1,"02/01/2018","{amount:4}"))

myCoin.addBlock(Block(2,"03/01/2018","{amount:5}"))

#print block info 打印区块链信息

print("print block info ####:")

for block in myCoin.chain:

print(block)

#check blockchain is valid 检查区块链是不是有效的

print("before tamper block,blockchain is valid ###")

print(myCoin.chainIsValid())

#tamper the blockinfo 篡改区块2的数据

myCoin.chain[1].data = "{amount:1002}"

print("after tamper block,blockchain is valid ###")

print(myCoin.chainIsValid())

输出结果

print block info ####:

{'index': 0, 'timestamp': '01/01/2018', 'data': 'genesis block', 'previousHash': '0', 'hash': 'd8d21e5ba33780d5eb77d09d3b407ceb8ade4e5545ef951de1997b209d91e264'}

{'index': 1, 'timestamp': '02/01/2018', 'data': '{amount:4}', 'previousHash': 'd8d21e5ba33780d5eb77d09d3b407ceb8ade4e5545ef951de1997b209d91e264', 'hash': '15426e32db30f4b26aa719ba5e573f372f41e27e4728eb9e9ab0bea8eae63a9d'}

{'index': 2, 'timestamp': '03/01/2018', 'data': '{amount:5}', 'previousHash': '15426e32db30f4b26aa719ba5e573f372f41e27e4728eb9e9ab0bea8eae63a9d', 'hash': '75119e897f21c769acee6e32abcefc5e88e250a1f35cc95946379436050ac2f0'}

before tamper block,blockchain is valid ###

True

after tamper block,blockchain is valid ###

False