廖雪峰Java10加密与安全-3摘要算法-3SHA-1算法

1.SHA-1算法

SHA-1算法也是一种哈希算法。

• 输出160 bits/20bytes
• 由美国国家安全局开发
• SHA-0/SHA-1/SHA-256/SHA-512
  
  * SHA-0有问题，已经作废了

算法	输出长度：bits	输出长度：bytes
SHA-1	160 bits	20 bytes
SHA-256	256 bits	32 bytes
SHA-512	512 bits	64 bytes

2.示例代码

SHA-1用法同MD5

import java.math.BigInteger;
import java.security.MessageDigest;
import java.util.Arrays;

public class SplitString {
    public static void main(String[] args) throws Exception {
        SplitString ns = new SplitString("helloworld");
        String[] ng = {"hello","world"};
        SplitString ns2 = new SplitString(ng);
    }
    public SplitString(String[] ss) throws Exception {
        MessageDigest md = MessageDigest.getInstance("SHA-1");
        for(String s:ss){
            md.update(s.getBytes("UTF-8"));
        }
        byte[] br = md.digest();
        String result = String.format("%032x",new BigInteger(1,br));
        System.out.println(Arrays.toString(ss)+"：\t"+result);
    }
    public SplitString(String s) throws Exception{
        String[] ss = {s,};
        new SplitString(ss);
    }
}

## 3.优化算法代码，可以指定算法
```#java
package com.testList;

import java.math.BigInteger;

import java.security.MessageDigest;

import java.util.Arrays;

public class SplitString {

public static byte[] digest(String hashAlggorithm, byte[] input){

MessageDigest md;

try{

md = MessageDigest.getInstance(hashAlggorithm);

}catch (Exception e){

throw new RuntimeException(e);

}

md.update(input);

return md.digest();

}

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

String s = "Java摘要算法测试";

byte[] input = s.getBytes("UTF-8");

byte[] r1 = digest("MD5",input);

System.out.println(r1.length+":"+String.format("%0"+(r1.length2)+"x",new BigInteger(1,r1)));

byte[] r2 = digest("SHA-1",input);

System.out.println(r2.length+":"+String.format("%0"+(r2.length2)+"x",new BigInteger(1,r2)));

byte[] r3 = digest("SHA-256",input);

System.out.println(r3.length+":"+String.format("%0"+(r3.length2)+"x",new BigInteger(1,r3)));

byte[] r4 = digest("RipeMD160",input);

System.out.println(r4.length+":"+String.format("%0"+(r4.length2)+"x",new BigInteger(1,r4)));

}

<img src="https://img2018.cnblogs.com/blog/1418970/201905/1418970-20190508220053277-957444074.png" width="500" />
[通过oracle官网可以查看](https://docs.oracle.com/javase/8/docs/api/javax/xml/crypto/dsig/DigestMethod.html)
##    4.总结：
*    SHA-1算法是比MD5更安全的哈希算法
*    其他哈希算法：SHA-256/SHA-512/RipeMD160

##    5.问题：
###    5.1 为什么经过哈希算法处理后，输出的字符串是byte数组长度的2倍
原因：byte转化为16进制是2位，因此数组的长度乘以2，即是输出字符串的长度
```#java
import java.math.BigInteger;
import java.security.MessageDigest;
import java.util.ArrayList;
import java.util.Arrays;

public class SplitString {
    public static byte[] digest(String hashAlggorithm, byte[] input){
        MessageDigest md;
        try{
            md = MessageDigest.getInstance(hashAlggorithm);
        }catch (Exception e){
            throw new RuntimeException(e);
        }
        md.update(input);
        return md.digest();
    }
    public static void main(String[] args) throws Exception{

        String s = "Java摘要算法测试";
        byte[] input = s.getBytes("UTF-8");
        byte[] r1 = digest("MD5",input);
        System.out.println(r1.length+":"+String.format("%0"+(r1.length*2)+"x",new BigInteger(1,r1)));
        //为什么输出的长度是byte长度的2位
        //byte转化为16进制是2位，因此数组的长度乘以2，即是输出字符串的长度
        System.out.println(Arrays.toString(r1));
        for(byte b:r1){
            System.out.print(Integer.toHexString(b)+"\t");
        }
    }
}