工作量证明及哈希算法

什么是工作量证明：
1、工作的结果作为数据加入区块链成为一个区块
2、完成这个工作的人会获得奖励（这也就是通过挖矿获得比特币）
3、整个“努力工作并进行证明”的机制，就叫工作量证明

为什么采用哈希算法：
1、不可逆：无法从一个哈希值恢复原始数据，哈希并不是加密
2、唯一性：对于特定的数据，只能有一个哈希值，并且这个哈希值是唯一的
3、防篡改：改变输入数据中的一个字节，导致输出一个完全不同的哈希

哈希算法特征：
1、正向快速：给定明文和hash算法，在有限时间和有限资源内能计算出hash值
2、逆向困难：给定hash值，在有限时间内很难逆推出明文
3、输入敏感：原始输入信息修改一点信息，产生的hash值会有很大的不同
4、冲突避免：很难找到两段内容不同的明文，使得他们的hash值一致（发生冲突）

main.go

package main

import (
	"core"
	"fmt"
	"strconv"
)

func main() {

	bc := core.NewBlockChain()

	bc.AddBlock("Send 1 BC to Ivan")
	bc.AddBlock("Send more BC to Ivan")

	for _,block := range bc.Blocks {
		fmt.Printf("Prev hash: %x\n", block.PrevBlockHash)
		fmt.Printf("Data: %s\n", block.Data)
		fmt.Printf("Hash: %x\n", block.Hash)
		//创建工作量证明
		pow := core.NewProofOfWork(block)
		//验证工作量证明
		fmt.Printf("Pow: %s\n", strconv.FormatBool(pow.Validate()))
		fmt.Println()
	}

}

　block.go

package core

import (
	"time"
	"strconv"
	"bytes"
	"crypto/sha256"
)

//Block keeps block header
type Block struct {
	Timestamp 		int64 	//区块创建的时间
	Data 	  		[]byte 	//区块包含的数据
	PrevBlockHash   []byte  //前一个区块的哈希值
	Hash 			[]byte  //区块自身的哈希值，用于校验区块数据有效
	Nonce 			int		//记录工作量证明用到的数字
}

//NewBlock create and returns Block
func NewBlock(data string, prevBlockHash []byte) *Block {
	block := &Block{
		Timestamp:time.Now().Unix(),
		Data: []byte(data),
		PrevBlockHash: prevBlockHash,
		Hash: []byte{},
	}

	pow := NewProofOfWork(block) //新建工作量证明
	nonce,hash := pow.Run()  //执行工作量证明(挖矿)
	block.Hash = hash
	block.Nonce = nonce
	return block
}

func (b *Block) SetHash() {
	timestamp := []byte(strconv.FormatInt(b.Timestamp, 10))
	headers := bytes.Join([][]byte{b.PrevBlockHash, b.Data, timestamp},[]byte{})
	hash := sha256.Sum256(headers)
	b.Hash = hash[:]
}

//NewGenesisBlock create and returns genesis Block
func NewGenesisBlock() *Block {
	return NewBlock("Genesis Block", []byte{})
}

　proofofwork.go

package core

import (
	"math"
	"math/big"
	"fmt"
	"crypto/sha256"
	"bytes"
)

var (
	maxNonce = math.MaxInt64
)

const targetBits  = 20

//ProofOfWork represents a proof-of-work
type ProofOfWork struct {
	block *Block
	target *big.Int
}

//NewProofOfWork builds and returns a ProofOfWork
func NewProofOfWork(b *Block) *ProofOfWork {
	target := big.NewInt(1)
	target.Lsh(target,uint(256-targetBits))

	pow := &ProofOfWork{b, target}

	return pow
}

func (pow *ProofOfWork) prepareData(nonce int) []byte {
	data := bytes.Join(
		[][]byte{
			pow.block.PrevBlockHash,
			pow.block.Data,
			IntToHex(int64(pow.block.Timestamp)),
			IntToHex(int64(nonce)),
		},
		[]byte{},
	)
	return data
}

func (pow *ProofOfWork) Run() (int, []byte) {
	var hashInt big.Int
	var hash [32]byte
	nonce := 0

	fmt.Printf("Mining the block containing \"%s\"\n", pow.block.Data)

	for nonce < maxNonce {
		data := pow.prepareData(nonce)

		hash = sha256.Sum256(data)
		fmt.Printf("\r%x", hash)
		hashInt.SetBytes(hash[:])

		if hashInt.Cmp(pow.target) == -1 {
			break
		}else{
			nonce++
		}
	}
	fmt.Print("\n\n")
	return nonce,hash[:]
}

func (pow *ProofOfWork) Validate() bool {
	var hashInt big.Int
	data := pow.prepareData(pow.block.Nonce)
	hash := sha256.Sum256(data)
	hashInt.SetBytes(hash[:])
	isValid := hashInt.Cmp(pow.target) == -1

	return isValid
}

　utils.go

package core

import (
	"bytes"
	"encoding/binary"
	"log"
)

func IntToHex(num int64) []byte {
	buff := new(bytes.Buffer)
	err := binary.Write(buff, binary.BigEndian, num)

	if err != nil {
		log.Panic(err)
	}

	return buff.Bytes()
}

　打印结果：

Mining the block containing "Genesis Block"
00000965faabec60c056cc30d9e6e45a0db7cfa84cb5897d8d5bdaa96971bd5f

Mining the block containing "Send 1 BC to Ivan"
000006910ca6331d7c640787defe1189fb158bc3d624949bc61b68a3f0031efc

Mining the block containing "Send more BC to Ivan"
00000a9e4f7f891bf6dd7323a1a5b698d5ba88c9363c8f5c9676fd075d526796

Prev hash:
Data: Genesis Block
Hash: 00000965faabec60c056cc30d9e6e45a0db7cfa84cb5897d8d5bdaa96971bd5f
Pow: true

Prev hash: 00000965faabec60c056cc30d9e6e45a0db7cfa84cb5897d8d5bdaa96971bd5f
Data: Send 1 BC to Ivan
Hash: 000006910ca6331d7c640787defe1189fb158bc3d624949bc61b68a3f0031efc
Pow: true

Prev hash: 000006910ca6331d7c640787defe1189fb158bc3d624949bc61b68a3f0031efc
Data: Send more BC to Ivan
Hash: 00000a9e4f7f891bf6dd7323a1a5b698d5ba88c9363c8f5c9676fd075d526796
Pow: true

来源：https://www.cnblogs.com/coder-886/p/9777350.html