廖雪峰Java10加密与安全-3摘要算法-5Hmac

1 比较MD5和HamcMD5

HmacMD5可以看作带安全salt的MD5

import javax.crypto.KeyGenerator;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.Security;

public class SplitString {
    public static void getMD5(String text,String salt) throws Exception{
        //使用salt+MD5加密
        byte[] data = text.getBytes("UTF-8");
        byte[] bslat = salt.getBytes("UTF-8");
        MessageDigest md = MessageDigest.getInstance("MD5");
        md.update(bslat);
        md.update(data);
        byte[] result = md.digest();
        System.out.println(String.format("MD5加密：%0"+result.length+"x",new BigInteger(1,result)));
    }
    public static void getHmac(String text) throws Exception{
        byte[] data = text.getBytes("UTF-8");

        // 获取KeyGenerator实例
        KeyGenerator keyGen = KeyGenerator.getInstance("HmacSHA1");
        //获取一个随机的Key
        SecretKey skey = keyGen.generateKey();

        //获取一个Mac的实例
        Mac mac = Mac.getInstance("HmacSHA1");
        //先传入SecretKey，初始化
        mac.init(skey);
        //再计算输入数据的MD5
        mac.update(data);
        System.out.println(String.format("HmacSHA1加密：%0"+mac.doFinal().length*2+"x",new BigInteger(1,mac.doFinal())));

        //打印SecretKey
        byte[] key = skey.getEncoded();
        System.out.println(String.format("Key:%0"+(key.length*2)+"x",new BigInteger(1,key)));
    }
    public static void main(String[] args) throws Exception{
        String text = "hello 美女";
        String salt = "stand up";
        getMD5(text,salt);
        getHmac(text);
    }
}

## 2 代码示例
```#java
import javax.crypto.KeyGenerator;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
import java.math.BigInteger;

public class SplitString {

public static byte[] hma(String hamcAlgorithm, SecretKey skey,byte[] data) throws Exception{

Mac mac = Mac.getInstance(hamcAlgorithm);

mac.init(skey);

mac.update(data);

return mac.doFinal();

}

public static void main(String[] args) throws Exception{

String[] algorithms = {"HmacMD5","HmacSHA1","HmacSHA256"};

String text = "hello world";

for(String s:algorithms){

KeyGenerator keyGen = KeyGenerator.getInstance(s);

SecretKey key = keyGen.generateKey();

byte[] data = text.getBytes("UTF-8");

byte[] reslut = hma(s,key,data);

System.out.println(String.format(s+":\t%0"+reslut.length*2+"x",new BigInteger(1,reslut))+"\t"+reslut.length);

}

}

}

<img src="https://img2018.cnblogs.com/blog/1418970/201905/1418970-20190510202600574-1584124211.png" width="500" />

##    3 总结：
*    Hmac是把Key混入摘要的算法
*    可以配合MD5、SHA-1等摘要算法
*    摘要长度和原摘要算法长度相同