基于Java语言构建区块链（二）—— 工作量证明

SHA256("wangwei1") ——> 1e898b7c9adaad86c20139a302ccd5277f81040cab68dc2aecfc684773532652
SHA256("wangwei2") ——> c9cc7417c17318c8aab448cc8ace24c53b6dcf350f5c5fd8e91cbc3b011a179d

# 计算字符串'I like donuts'的哈希值
SHA256("I like donuts") 
——> f80867f6efd4484c23b0e7184e53fe4af6ab49b97f5293fcd50d5b2bfa73a4d0

# 拼接一个计数器值(ca07ca)，再次进行Hash计算
SHA256("I like donutsca07ca") 
——> 0000002f7c1fe31cb82acdc082cfec47620b7e4ab94f2bf9e096c436fc8cee06

/**
 * 工作量证明
 *
 * @author wangwei
 * @date 2018/02/04
 */
@Data
public class ProofOfWork {

    /**
     * 难度目标位
     */
    public static final int TARGET_BITS = 20;

    /**
     * 区块
     */
    private Block block;
    /**
     * 难度目标值
     */
    private BigInteger target;

    private ProofOfWork(Block block, BigInteger target) {
        this.block = block;
        this.target = target;
    }
  
    /**
     * 创建新的工作量证明，设定难度目标值
     * <p>
     * 对1进行移位运算，将1向左移动 (256 - TARGET_BITS) 位，得到我们的难度目标值
     * 
     * @param block
     * @return 
     */
    public static ProofOfWork newProofOfWork(Block block) {
        BigInteger targetValue = BigInteger.valueOf(1).shiftLeft((256 - TARGET_BITS));
        return new ProofOfWork(block, targetValue);
    }
}

/**
 * 准备数据
 * <p>
 * 注意：在准备区块数据时，一定要从原始数据类型转化为byte[]，不能直接从字符串进行转换
 * @param nonce
 * @return
 */
private String prepareData(long nonce) {
   byte[] prevBlockHashBytes = {};
   if (StringUtils.isNoneBlank(this.getBlock().getPrevBlockHash())) {
       prevBlockHashBytes = new BigInteger(this.getBlock().getPrevBlockHash(), 16).toByteArray();
   }

   return ByteUtils.merge(
           prevBlockHashBytes,
           this.getBlock().getData().getBytes(),
           ByteUtils.toBytes(this.getBlock().getTimeStamp()),
           ByteUtils.toBytes(TARGET_BITS),
           ByteUtils.toBytes(nonce)
    );
}

/**
 * 运行工作量证明，开始挖矿，找到小于难度目标值的Hash
 *
 * @return
 */
public PowResult run() {
    long nonce = 0;
    String shaHex = "";
    System.out.printf("Mining the block containing：%s \n", this.getBlock().getData());

    long startTime = System.currentTimeMillis();
    while (nonce < Long.MAX_VALUE) {
        String data = this.prepareData(nonce);
        shaHex = DigestUtils.sha256Hex(data);
        if (new BigInteger(shaHex, 16).compareTo(this.target) == -1) {
            System.out.printf("Elapsed Time: %s seconds \n", (float) (System.currentTimeMillis() - startTime) / 1000);
            System.out.printf("correct hash Hex: %s \n\n", shaHex);
            break;
         } else {
            nonce++;
         }
     }
     return new PowResult(nonce, shaHex);
}

/**
 * 验证区块是否有效
 *
 * @return
 */
public boolean validate() {
    String data = this.prepareData(this.getBlock().getNonce());
    return new BigInteger(DigestUtils.sha256Hex(data), 16).compareTo(this.target) == -1;
}

/**
 * <p> 创建新区块 </p>
 *
 * @param previousHash
 * @param data
 * @return
 */
public static Block newBlock(String previousHash, String data) {
    Block block = new Block("", previousHash, data, Instant.now().getEpochSecond(), 0);
    ProofOfWork pow = ProofOfWork.newProofOfWork(block);
    PowResult powResult = pow.run();
    block.setHash(powResult.getHash());
    block.setNonce(powResult.getNonce());
    return block;
}

/**
 * 测试
 *
 * @author wangwei
 * @date 2018/02/05
 */
public class BlockchainTest {

    public static void main(String[] args) {

        Blockchain blockchain = Blockchain.newBlockchain();

        blockchain.addBlock("Send 1 BTC to Ivan");
        blockchain.addBlock("Send 2 more BTC to Ivan");

        for (Block block : blockchain.getBlockList()) {
            System.out.println("Prev.hash: " + block.getPrevBlockHash());
            System.out.println("Data: " + block.getData());
            System.out.println("Hash: " + block.getHash());
            System.out.println("Nonce: " + block.getNonce());

            ProofOfWork pow = ProofOfWork.newProofOfWork(block);
            System.out.println("Pow valid: " +  pow.validate() + "\n");
        }
    }
}

/**
 * 设定TARGET_BITS = 20，得到如下结果：
 */
Mining the block containing：Genesis Block 
Elapsed Time: 2.118 seconds 
correct hash Hex: 00000828ee8289ef6381f297585ef8c952fde93fc2b673ff7cc655f699bb2442 

Mining the block containing：Send 1 BTC to Ivan 
Elapsed Time: 1.069 seconds 
correct hash Hex: 00000a38c0d7f2ebbd20773e93770298aa8bc0cc6d85fca8756fe0646ae7fea5 

Mining the block containing：Send 2 more BTC to Ivan 
Elapsed Time: 4.258 seconds 
correct hash Hex: 00000777f93efe91d9aabcba14ab3d8ab8e0255b89818cdb9b93cfa844ad0c7f 

Prev.hash: 
Data: Genesis Block
Hash: 00000828ee8289ef6381f297585ef8c952fde93fc2b673ff7cc655f699bb2442
Nonce: 522163
Pow valid: true

Prev.hash: 00000828ee8289ef6381f297585ef8c952fde93fc2b673ff7cc655f699bb2442
Data: Send 1 BTC to Ivan
Hash: 00000a38c0d7f2ebbd20773e93770298aa8bc0cc6d85fca8756fe0646ae7fea5
Nonce: 474758
Pow valid: true

Prev.hash: 00000a38c0d7f2ebbd20773e93770298aa8bc0cc6d85fca8756fe0646ae7fea5
Data: Send 2 more BTC to Ivan
Hash: 00000777f93efe91d9aabcba14ab3d8ab8e0255b89818cdb9b93cfa844ad0c7f
Nonce: 1853839
Pow valid: true