The SHA hash functions are a set of cryptographic hash functions designed by the National Security Agency (NSA) and published by the NIST as a U.S. Federal Information Processing Standard. SHA stands for Secure Hash Algorithm. The three SHA algorithms are structured differently and are distinguished as SHA-0, SHA-1, and SHA-2. The SHA-2 family uses an identical algorithm with a variable digest size which is distinguished as SHA-224, SHA-256, SHA-384, and SHA-512.

SHA-2 is believe the most secure hashing algorithm as this article is written, here are few examples for the SHA implementation. The possible MessageDigest algorithm are SHA-1, SHA-256, SHA-384, and SHA-512, you can check the reference for the detail.

1. File checksum with SHA-256

It will use SHA-256 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 SHACheckSumExample 
{
    public static void main(String[] args)throws Exception
    {
        MessageDigest md = MessageDigest.getInstance("SHA-256");
        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("Hex format : " + sb.toString());
 
       //convert the byte to hex format method 2
        StringBuffer hexString = new StringBuffer();
    	for (int i=0;i<mdbytes.length;i++) {
    	  hexString.append(Integer.toHexString(0xFF & mdbytes[i]));
    	}
 
    	System.out.println("Hex format : " + hexString.toString());
    }
}
Output
Hex format : 21a57f2fe765e1ae4a8bf15d73fc1bf2a533f547f2343d12a499d9c0592044d4
Hex format : 21a57f2fe765e1ae4a8bf15d73fc1bf2a533f547f2343d12a499d9c0592044d4

2. Hashing String with SHA-256

It will use SHA-256 hashing algorithm to generate a hash value for a password “123456″.

package com.mkyong.test;
 
import java.security.MessageDigest;
 
public class SHAHashingExample 
{
    public static void main(String[] args)throws Exception
    {
    	String password = "123456";
 
        MessageDigest md = MessageDigest.getInstance("SHA-256");
        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("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("Hex format : " + hexString.toString());
    }
}
Output
Hex format : 8d969eef6ecad3c29a3a629280e686cf0c3f5d5a86aff3ca12020c923adc6c92
Hex format : 8d969eef6ecad3c29a3a629280e686cf0c3f5d5a86aff3ca12020c923adc6c92

Reference

  1. http://en.wikipedia.org/wiki/SHA_hash_functions
  2. http://java.sun.com/j2se/1.4.2/docs/guide/security/CryptoSpec.html#AppA
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