init repo

content/post/014.区块链学习笔记——概念与简单JS实现/区块链学习笔记——概念与简单JS实现.md

@@ -0,0 +1,180 @@
+---
+title: "区块链学习笔记——概念与简单JS实现"
+categories: [ "程序人生","开源项目","算法解析" ]
+tags: [  ]
+draft: false
+slug: "blockchain-01"
+date: "2020-07-12 16:28:00"
+---
+
+在哔哩哔哩上看 [是落拓呀][1] 的区块链简明教程，趁热打铁，把自己学习过程记录下来
+本项目的 Github 地址 ↓
+[github repo="taurusxin/taurusxincoin" /]
+
+## 区块
+区块即是每一次的交易，比如A转账给B十元，那么这条交易就写在这个区块内
+区块里面实际包含的是
+
+ - 交易数据
+ - 本次交易的 hash
+ - 前一次交易的 hash
+
+其中本一次交易的 hash 为 "本次交易的数据 + 上一次交易的hash" 的 hash 值
+用简明的伪代码表示就是
+
+```javascript
+Block = {
+  data = '',
+  hash = sha256(data + previousHash),
+  previousHash = ''
+}
+```
+
+## 链
+链就是一系列区块的总和，与之相联通的就是 hash 值，每一次的交易都有它的 hash，与链表的作用机制相似
+可以理解为一个链表，简明代码表示就是一个数组
+
+```javascript
+Chain = {
+  blocks[Block]
+}
+```
+
+## JS实现
+这里用 node.js 来实现一个简单的区块链
+
+初始化项目，安装 crypto-js 依赖
+```cmd
+npm init
+npm install crypto-js -S
+```
+
+构建 Block 和 Chain 对象
+```javascript
+class Block {
+  constructor(data, previousHash) {
+    this.data = data
+    this.previousHash = previousHash
+    this.hash = this.computeHash()
+  }
+
+  computeHash() {
+    return sha256(this.data + this.previousHash).toString()
+  }
+}
+```
+构造函数传入了这个对象的 `data` `previousHash` 数据，然后定义了对象成员 `hash` ，用于计算当前区块的 hash
+```javascript
+class Chain {
+  constructor() {
+    this.chain = [this.bigBang()]
+  }
+
+  bigBang() {
+    const genisisBlcok = new Block('我是祖先', '')
+    return genisisBlcok
+  }
+
+  getLatestBlock() {
+    return this.chain[this.chain.length - 1]
+  }
+
+  addBlockToChain(newBlock) {
+    // find the nearest block's hash
+    // which is the new block's previous hash
+    newBlock.previousHash = this.getLatestBlock().hash
+    newBlock.hash = newBlock.computeHash()
+    this.chain.push(newBlock)
+  }
+
+  // check the previous hash is equal to previous block's hash
+  validateChain() {
+    if (this.chain.length === 1) {
+      if (this.chain[0].hash !== this.chain[0].computeHash()) {
+        return false
+      }
+      return true
+    }
+    // check if current data has been change
+    for (let i = 1; i < this.chain.length; i++) {
+      const blockToValidate = this.chain[i]
+      if (blockToValidate.hash !== blockToValidate.computeHash()) {
+        console.log('data has been change')
+        return false
+      }
+
+      const previousBlcok = this.chain[i - 1]
+      if (blockToValidate.previousHash !== previousBlcok.hash) {
+        console.log('previous and current block lost connection')
+        return false
+      }
+    }
+    return true
+  }
+}
+```
+最初始的 `chain` 只包含一个祖先区块，它没有 `previousHash`，并用 `bigBang` 方法进行初始化，`addBlockToChain` 方法实现了添加一个区块，并自动计算其 hash
+`validateChain()` 方法，从三种情况去校验这个链是否合法。
+ 1. 只有一个祖先区块时，校验祖先区块数据是否被篡改
+ 2. 从第二个区块开始遍历是否有数据被篡改
+ 3. 从第二个区块开始遍历是否有hash值被修改
+
+检验代码是否有效
+```js
+const taurusxinChain = new Chain()
+
+const block1 = new Block('转账十元', '')
+taurusxinChain.addBlockToChain(block1)
+const block2 = new Block('转账十个十元', '')
+taurusxinChain.addBlockToChain(block2)
+
+console.log(taurusxinChain)
+console.log(taurusxinChain.validateChain())
+
+// try to change the block data
+taurusxinChain.chain[1].data = '转账一百个十元'
+console.log(taurusxinChain.validateChain())
+
+// try to change the block hash
+taurusxinChain.chain[1].hash = taurusxinChain.chain[1].computeHash()
+console.log(taurusxinChain.validateChain())
+```
+
+输出结果
+```
+Chain {
+  chain: [
+    Block {
+      data: '我是祖先',
+      previousHash: '',
+      hash: 'dbf4cebe91cf0212be8ee04289855fc17e0085d45a7b4c69eeb79e7c636b48fc'
+    },
+    Block {
+      data: '转账十元',
+      previousHash: 'dbf4cebe91cf0212be8ee04289855fc17e0085d45a7b4c69eeb79e7c636b48fc',
+      hash: 'f135810d2aa85703b2f7356877b95de3dad00955830d570568dd42dd52b93500'
+    },
+    Block {
+      data: '转账十个十元',
+      previousHash: 'f135810d2aa85703b2f7356877b95de3dad00955830d570568dd42dd52b93500',
+      hash: 'ec3caa66201967755657f30156f38207de23c897caa9aa3ca972f413b9a6a749'
+    }
+  ]
+}
+true
+data has been change
+false
+previous and current block lost connection
+false
+```
+第一次生成区块链，校验成功，输出true
+尝试更改第二个区块的数据，输出 `data has been change`
+尝试更改第二个区块的hash值，输出 `previous and current block lost connection`
+
+## 下一阶段
+
+ - 工作量证明
+ - 生成钱包地址
+ - 加密
+
+  [1]: https://space.bilibili.com/43276908/