初識區塊鏈——用JS構建你本身的區塊鏈

時間 2019-12-06

標籤區塊構建本身欄目比特幣简体版

原文原文鏈接

前言

區塊鏈太複雜，那咱們就講點簡單的。用JS來構建你本身的區塊鏈系統，寥寥幾行代碼就能夠說明區塊鏈的底層數據結構、POW挖礦思想和交易過程等。固然了，真實的場景遠遠遠比這複雜。本文的目的僅限於讓你們初步瞭解、初步認識區塊鏈。node

文章內容主要參考視頻：Building a blockchain with Javascript (https://www.youtube.com/playlist?list=PLzvRQMJ9HDiTqZmbtFisdXFxul5k0F-Q4)數組

感謝原做者，本文在原視頻基礎上作了修改補充，並加入了我的理解。數據結構

認識區塊鏈

區塊鏈顧名思義是由區塊鏈接而成的鏈，所以最基本的數據結構是Block。每一個Block都含有timestamp、data、hash、previousHash等信息。其中data用來存儲數據，previousHash是前一個區塊的hash值。示意以下：區塊鏈

hash是對區塊信息的摘要存儲，hash的好處是任意長度的信息通過hash均可以映射成固定長度的字符串，如可用sha256：ui

calculateHash() {
    return SHA256(this.previousHash + this.timestamp + JSON.stringify(this.data)).toString();
}

Block的數據結構

Block的最基本數據結構以下：this

class Block {
    constructor(timestamp, data, previousHash = '') {
        this.timestamp = timestamp;
        this.data = data;
        this.previousHash = previousHash;
        //對hash的計算必須放在最後，保證全部數據賦值正確後再計算
        this.hash = this.calculateHash(); 
    }

    calculateHash() {
        return SHA256(this.previousHash + this.timestamp + JSON.stringify(this.data)).toString();
    }
}

BlockChain的數據結構

多個Block連接而成BlockChain，顯然可用用數組或鏈表來表示，如：spa

class BlockChain {
    constructor() {
        this.chain = [];
    }
}

創世區塊

正所謂萬物始於一，區塊鏈的第一個區塊老是須要人爲來手動建立，這個區塊的previousHash爲空，如：code

createGenesisBlock() {
    return new Block("2018-11-11 00:00:00", "Genesis block of simple chain", "");
}

區塊鏈的構造方法也應改成：視頻

class BlockChain {
    constructor() {
        this.chain = [this.createGenesisBlock()];
    }
}

添加區塊

每新加一個區塊，必須保證與原有區塊鏈鏈接起來，即：blog

class BlockChain {
    getLatestBlock() {
        return this.chain[this.chain.length - 1];
    }
    
    addBlock(newBlock) {
        //新區塊的前一個hash值是現有區塊鏈的最後一個區塊的hash值；
        newBlock.previousHash = this.getLatestBlock().hash;
        //從新計算新區塊的hash值（由於指定了previousHash)；
        newBlock.hash = newBlock.calculateHash(); 
        //把新區塊加入到鏈中；
        this.chain.push(newBlock); 
    }
    ...
}

校驗區塊鏈

區塊鏈數據結構的核心是保證先後連接、沒法篡改，可是若是有人真的篡改了某個區塊，咱們該如何校驗發現呢？最笨也是最天然是想法就是遍歷全部狀況，逐一校驗，如：

isChainValid() {
    //遍歷全部區塊
    for (let i = 1; i < this.chain.length; i++) {
        const currentBlock = this.chain[i];
        const previousBlock = this.chain[i - 1];
        //從新計算當前區塊的hash值，若發現hash值對不上，說明該區塊有數據被篡改，hash值未從新計算
        if (currentBlock.hash !== currentBlock.calculateHash()) {
            console.error("hash not equal: " + JSON.stringify(currentBlock));
            return false;
        }
        //判斷當前區塊的previousHash是否真的等於前一個區塊的hash，若不等，說明前一個區塊被篡改，雖然hash值被從新計算正確，可是後續區塊的hash值並未從新計算，致使整個鏈斷裂
        if (currentBlock.previousHash !== previousBlock.calculateHash) {
            console.error("previous hash not right: " + JSON.stringify(currentBlock));
            return false;
        }
    }
    return true;
}

Just run it

跑起來看看，即：

let simpleChain = new BlockChain();
simpleChain.addBlock(new Block("2018-11-11 00:00:01", {amount: 10}));
simpleChain.addBlock(new Block("2018-11-11 00:00:02", {amount: 20}));


console.log(JSON.stringify(simpleChain, null, 4));

console.log("is the chain valid? " + simpleChain.isChainValid());

結果以下：

ali-186590cc4a7f:simple-chain shanyao$ node main_1.js 
{
    "chain": [
        {
            "timestamp": "2018-11-11 00:00:00",
            "data": "Genesis block of simple chain",
            "previousHash": "",
            "hash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89"
        },
        {
            "timestamp": "2018-11-11 00:00:01",
            "data": {
                "amount": 10
            },
            "previousHash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89",
            "hash": "150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529"
        },
        {
            "timestamp": "2018-11-11 00:00:02",
            "data": {
                "amount": 20
            },
            "previousHash": "150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529",
            "hash": "274a7a13ed20118e8cb745654934a7e24a4d59333ba17dfbf5d4cfe0fa8a6e34"
        }
    ]
}
is the chain valid? true

注意看其中的previousHash與hash，確實是當前區塊的previousHash指向前一個區塊的hash。

篡改下試試

都說區塊鏈不可篡改，是真的嗎？讓咱們篡改第2個區塊試試，如：

let simpleChain = new BlockChain();
simpleChain.addBlock(new Block("2018-11-11 00:00:01", {amount: 10}));
simpleChain.addBlock(new Block("2018-11-11 00:00:02", {amount: 20}));

console.log("is the chain valid? " + simpleChain.isChainValid());

//將第2個區塊的數據，由10改成15
simpleChain.chain[1].data = {amount: 15};

console.log("is the chain still valid? " + simpleChain.isChainValid());
console.log(JSON.stringify(simpleChain, null, 4));

結果以下：

ali-186590cc4a7f:simple-chain shanyao$ node main_1.js 
is the chain valid? true
hash not equal: {"timestamp":"2018-11-11 00:00:01","data":{"amount":15},"previousHash":"fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89","hash":"150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529"}
is the chain still valid? false
{
    "chain": [
        {
            "timestamp": "2018-11-11 00:00:00",
            "data": "Genesis block of simple chain",
            "previousHash": "",
            "hash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89"
        },
        {
            "timestamp": "2018-11-11 00:00:01",
            "data": {
                "amount": 15
            },
            "previousHash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89",
            "hash": "150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529"
        },
        {
            "timestamp": "2018-11-11 00:00:02",
            "data": {
                "amount": 20
            },
            "previousHash": "150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529",
            "hash": "274a7a13ed20118e8cb745654934a7e24a4d59333ba17dfbf5d4cfe0fa8a6e34"
        }
    ]
}

顯然，篡改了數據以後，hash值並未從新計算，致使該區塊的hash值對不上。

再篡改下試試

那麼，若是咱們聰明點，篡改後把hash值也從新計算會如何？

let simpleChain = new BlockChain();
simpleChain.addBlock(new Block("2018-11-11 00:00:01", {amount: 10}));
simpleChain.addBlock(new Block("2018-11-11 00:00:02", {amount: 20}));

console.log("is the chain valid? " + simpleChain.isChainValid());
//篡改後從新計算hash值
simpleChain.chain[1].data = {amount: 15};
simpleChain.chain[1].hash = simpleChain.chain[1].calculateHash();
console.log("is the chain still valid? " + simpleChain.isChainValid());
console.log(JSON.stringify(simpleChain, null, 4));

結果以下：

ali-186590cc4a7f:simple-chain shanyao$ node main_1.js 
is the chain valid? true
previous hash not right: {"timestamp":"2018-11-11 00:00:02","data":{"amount":20},"previousHash":"150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529","hash":"274a7a13ed20118e8cb745654934a7e24a4d59333ba17dfbf5d4cfe0fa8a6e34"}
is the chain still valid? false
{
    "chain": [
        {
            "timestamp": "2018-11-11 00:00:00",
            "data": "Genesis block of simple chain",
            "previousHash": "",
            "hash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89"
        },
        {
            "timestamp": "2018-11-11 00:00:01",
            "data": {
                "amount": 15
            },
            "previousHash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89",
            "hash": "74d139274fb692495b7c805dd5822faa0c5b5e6058b6beef96e87e18ab83a6b1"
        },
        {
            "timestamp": "2018-11-11 00:00:02",
            "data": {
                "amount": 20
            },
            "previousHash": "150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529",
            "hash": "274a7a13ed20118e8cb745654934a7e24a4d59333ba17dfbf5d4cfe0fa8a6e34"
        }
    ]
}

顯然，第3個區塊的previousHash並未指向第2個區塊的hash。

是真的沒法篡改嗎

其實並非，若是咱們再聰明一點，把後續區塊的hash值也從新計算一下，不就OK了嗎？確實如此，如：

let simpleChain = new BlockChain();
simpleChain.addBlock(new Block("2018-11-11 00:00:01", {amount: 10}));
simpleChain.addBlock(new Block("2018-11-11 00:00:02", {amount: 20}));

console.log("is the chain valid? " + simpleChain.isChainValid());
//篡改第2個區塊
simpleChain.chain[1].data = {amount: 15};
simpleChain.chain[1].hash = simpleChain.chain[1].calculateHash();
//並把第3個區塊也從新計算
simpleChain.chain[2].previousHash = simpleChain.chain[1].hash;
simpleChain.chain[2].hash = simpleChain.chain[2].calculateHash();
console.log("is the chain still valid? " + simpleChain.isChainValid());
console.log(JSON.stringify(simpleChain, null, 4

原文連接