// CS 1501 Summer 2006
// Handout to help you with your Digital Signature Assignment

import java.math.*;
import java.util.*;
import java.io.*;

public class ByteBigByte
{
	public static void main (String [] args) throws Exception
	{
	     byte [] orig1 = new byte[256];
		 byte [] orig2 = new byte[256];

	     for (int i = 0; i < orig1.length; i++)
	     {
			 orig1[i] = (byte) (i);     // this will have a leading 0 byte
			 orig2[i] = (byte) (255-i); // this have a leading negative byte 
		 }

         // Since byte values are signed in Java, values > 127 will have a leading
         // 1, and will be interpreted as negative values.  This may look odd but,
         // as shown below, it should not cause any problems with your encryption
         // and decryption (since the overall number is used, not the individual
		 // bytes.  However, since we need our BigInteger to be non-negative, we
		 // use the constructor shown below, which uses a "sign magnitude"
		 // system -- the 1 indicates the sign will be positive, and the byte
		 // array is used for the magnitude.

		 System.out.println("Orig1. array: ");
		 for (int i = 0; i < orig1.length; i++)
		 	System.out.print(orig1[i] + " ");
		 System.out.println();
		 
		 System.out.println("Orig2. array: ");
		 for (int i = 0; i < orig2.length; i++)
		 	System.out.print(orig2[i] + " ");
		 System.out.println();

		 BigInteger orig1Int = new BigInteger(1, orig1);
		 BigInteger orig2Int = new BigInteger(1, orig2);

		 System.out.println("First BigInt: " + orig1Int);
		 System.out.println("Second BigInt: " + orig2Int);
		 
		 // When BigIntegers are created from byte arrays, any unnecessary
		 // leading 0 bits are removed.  Thus, if your original byte array had
		 // a leading byte of all 0s that byte will be removed and will not
		 // appear when the BigInteger is converted back to a byte array. This
		 // can be handled by testing as shown below.

		 // On the other hand, if an extra 0 bit was added to make the value
		 // positive (the leading bit of the leftmost byte in the array was a 1),
		 // when converted back to a byte array, an extra byte will be allocated
		 // for that leading 0.  In this case, you want index values 1-128 in the array,
		 // rather than the normal 0-127.  Make sure you handle this situation correctly,
		 // as indicated below (in my code below, I KNOW what is in the arrays, but
		 // you will need to test in your code)

		 byte [] copy1 = orig1Int.toByteArray();
		 byte [] copy2 = orig2Int.toByteArray();

		 int copy1len = copy1.length;
		 int copy2len = copy2.length;

		 System.out.println("De-integerized array 1");
		 System.out.print("" + 0 + " "); // Indicate the 0 byte
		 for (int i = 0; i < copy1.length; i++)  // Print the array
		 {
		 	System.out.print(copy1[i] + " ");
		 }
		 System.out.println();
		 
		 System.out.println("De-integerized array 2");
		 for (int i = 1; i < copy2.length; i++)
		 {
		 	System.out.print(copy2[i] + " ");
		 }
		 System.out.println();

	}
}