//George Koutsogiannakis
//2/13/2007

import java.security.MessageDigest;
import java.io.FileInputStream;

public class createDigest
 
{
	public static void main(String[] args) 
	{
		byte[] mdbytes=new byte[1024];
		String datafile="createDigest.java";
		MessageDigest md=null;
		MessageDigest md1=null;
		try
		{

			md=MessageDigest.getInstance("SHA1");

			FileInputStream fis=new FileInputStream(datafile);

			byte[] dataBytes=new byte[1024];
			
			//read returns the number of bytes read. if n=-1 there are no more bytes
			int n=fis.read(dataBytes);
			//1024 bytes read and placed in the array
			System.out.println(n);
			System.out.println(dataBytes[0]);
			System.out.println(dataBytes[1023]);
			
			while(n>0)
			{
				//compute digest of bytes
				md.update(dataBytes, 0, n);
				n=fis.read(dataBytes);
				System.out.println("Byte Number"+" "+n);

			}

			mdbytes=md.digest();
			fis.close();
		}//end of try
		catch(Exception e) {}

		for(int i=0; i<=mdbytes.length-1; i++)
		{
			System.out.println("First Digest is:"+" "+mdbytes[i]);
		}
		
		//let 's do it over an dcraete another digest of the same data
		//then compare the two

		byte[] mdbytes1=new byte[1024];

		String datafile1="createDigest.java";
		try
		{
			
			md1=MessageDigest.getInstance("SHA1");

			FileInputStream fis1=new FileInputStream(datafile1);
			byte[] dataBytes1=new byte[1024];

			int m=fis1.read(dataBytes1);
			
			while(m>0)
			{
				md1.update(dataBytes1, 0, m);
				m=fis1.read(dataBytes1);
			}
			mdbytes1=md1.digest();
			fis1.close();
		}//end of try
		catch(Exception e){}

		for (int i=0; i<=mdbytes1.length-1; i++)
		{
				System.out.println("Second Digest is:"+" "+mdbytes1[i]);
		
		}
		if(md1.isEqual(mdbytes, mdbytes1))
		{
				System.out.println("The two digests are equal");
		}
		else
			System.out.println("The two digests are not equal");

	}//end of main

}//end of class


	
/*---------- Interpreter ----------
1024
Byte Number 839
Byte Number -1
First Digest is: -51
First Digest is: 56
First Digest is: -75
First Digest is: 110
First Digest is: -20
First Digest is: -40
First Digest is: -22
First Digest is: 102
First Digest is: 71
First Digest is: 116
First Digest is: 89
First Digest is: -120
First Digest is: -122
First Digest is: 64
First Digest is: 4
First Digest is: 71
First Digest is: -41
First Digest is: -36
First Digest is: -70
First Digest is: 44
Second Digest is: -51
Second Digest is: 56
Second Digest is: -75
Second Digest is: 110
Second Digest is: -20
Second Digest is: -40
Second Digest is: -22
Second Digest is: 102
Second Digest is: 71
Second Digest is: 116
Second Digest is: 89
Second Digest is: -120
Second Digest is: -122
Second Digest is: 64
Second Digest is: 4
Second Digest is: 71
Second Digest is: -41
Second Digest is: -36
Second Digest is: -70
Second Digest is: 44
The two digests are equal
Normal Termination
Output completed (0 sec consumed).
If the first digest was created by Jane and sent to Mike
Mike created the second digest and compared it to the one
sent by Jane*/