一致性hash 之 MD5hash算法

这里面提出了一个常见的错误,要注意 

http://www.bpsky.net/t/android%20md5%20%E5%8A%A0%E5%AF%86%E5%AD%97%E7%AC%A6%E4%B8%B2.html

Java MD5 Hashing Example

MD5 is one in a series of message digest algorithms designed by Professor Ronald Rivest of MIT (Rivest, 1994). When analytic work indicated that MD5′s predecessor MD4 was likely to be insecure, MD5 was designed in 1991 to be a secure replacement. (Weaknesses were indeed later found in MD4 by Hans Dobbertin.)

MD5 is a widely used hashing algorithm in many companies and industries, here are two examples for the MD5 implementation.

1. File checksum with MD5

It will use MD5 hashing algorithm to generate a checksum for file “c:\\loging.log”.

package com.mkyong.test;
 
import java.io.FileInputStream;
import java.security.MessageDigest;
 
public class MD5CheckSumExample 
{
    public static void main(String[] args)throws Exception
    {
        MessageDigest md = MessageDigest.getInstance("MD5");
        FileInputStream fis = new FileInputStream("c:\\loging.log");
 
        byte[] dataBytes = new byte[1024];
 
        int nread = 0; 
        while ((nread = fis.read(dataBytes)) != -1) {
          md.update(dataBytes, 0, nread);
        };
        byte[] mdbytes = md.digest();
 
        //convert the byte to hex format method 1
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < mdbytes.length; i++) {
          sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
        }
 
        System.out.println("Digest(in hex format):: " + sb.toString());
 
        //convert the byte to hex format method 2
        StringBuffer hexString = new StringBuffer();
    	for (int i=0;i<mdbytes.length;i++) {
    		String hex=Integer.toHexString(0xff & mdbytes[i]);
   	     	if(hex.length()==1) hexString.append('0');
   	     	hexString.append(hex);
    	}
    	System.out.println("Digest(in hex format):: " + hexString.toString());
    }
}

Output

 

Digest(in hex format):: e72c504dc16c8fcd2fe8c74bb492affa
Digest(in hex format):: e72c504dc16c8fcd2fe8c74bb492affa

2. Hashing String with MD5

It will use MD5 hashing algorithm to generate a hash value for a password “123456″.

package com.mkyong.test;
 
import java.security.MessageDigest;
 
public class MD5HashingExample 
{
    public static void main(String[] args)throws Exception
    {
    	String password = "123456";
 
        MessageDigest md = MessageDigest.getInstance("MD5");
        md.update(password.getBytes());
 
        byte byteData[] = md.digest();
 
        //convert the byte to hex format method 1
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < byteData.length; i++) {
         sb.append(Integer.toString((byteData[i] & 0xff) + 0x100, 16).substring(1));
        }
 
        System.out.println("Digest(in hex format):: " + sb.toString());
 
        //convert the byte to hex format method 2
        StringBuffer hexString = new StringBuffer();
    	for (int i=0;i<byteData.length;i++) {
    		String hex=Integer.toHexString(0xff & byteData[i]);
   	     	if(hex.length()==1) hexString.append('0');
   	     	hexString.append(hex);
    	}
    	System.out.println("Digest(in hex format):: " + hexString.toString());
    }
}

Output

Digest(in hex format):: e10adc3949ba59abbe56e057f20f883e
Digest(in hex format):: e10adc3949ba59abbe56e057f20f883e

Reference

1. http://en.wikipedia.org/wiki/MD5
2. http://forums.sun.com/thread.jspa?threadID=5169003