rsaimp.java

RSA implementation by using Java

package cpe5021;
import java.math.BigInteger;
import java.util.Scanner;
import sun.security.util.BigInt;

	public class RsaImp {

	   private final static BigInteger ONE = new BigInteger("1");
	   
	   private BigInteger privateKey;
	   private BigInteger publicKey;
	   private BigInteger modulus;

	   RsaImp(int N) {
		   Modules modules = new Modules();
		   
		   BigInteger p = modules.getRandomPrime(N);
		   BigInteger q = new BigInteger("0");
		   do {
			   q = modules.getRandomPrime(N);
		   }while (p.equals(q)||!GCD(p,q).equals(BigInteger.ONE));
	      
		   BigInteger phi = (p.subtract(ONE)).multiply(q.subtract(ONE));

		   modulus    = p.multiply(q);                                  
		   publicKey  = modules.getRandomPrime(16);
		   privateKey = publicKey.modInverse(phi);
		   
	   }

	   BigInteger encrypt(BigInteger message) {
	      return message.modPow(publicKey, modulus);
	   }

	   BigInteger decrypt(BigInteger encrypted) {
	      return encrypted.modPow(privateKey, modulus);
	   }

	   BigInteger signature(BigInteger message){
		  return message.modPow(privateKey, modulus);
	   }
	   
	   BigInteger revert(BigInteger signatured){
		  return signatured.modPow(publicKey, modulus);
	   }
	 
	   public BigInteger GCD(BigInteger a, BigInteger b)
	   {
		   if (b.equals(BigInteger.ZERO)) return a;
		   return GCD(b,a.mod(b));
	   }
	   
	   public static void main(String[] args) {
	      System.out.print("Please type in key size: ");
		  Scanner scan = new Scanner(System.in);
	      int num = scan.nextInt();
	      
		  System.out.print("Please type in messages: ");
	      Scanner s = new Scanner(System.in);
	      String m = s.nextLine();
	      
	      RsaImp key = new RsaImp(num);
		  
	      byte[] bytes = m.getBytes();
	      BigInteger message = new BigInteger(bytes);
		  
	      BigInteger encrypt = key.encrypt(message);
	      BigInteger decrypt = key.decrypt(encrypt);
	      BigInteger signature = key.signature(message);
	      BigInteger revert = key.revert(signature);
	      
	      byte[] en = encrypt.toByteArray();
	      byte[] de = decrypt.toByteArray();
	      byte[] si = signature.toByteArray();
	      byte[] re = revert.toByteArray();
	    	  
	      String enm = new String(en);
	      String dem = new String(de);
	      String sim = new String(si);
	      String rem = new String(re);
	      
	      System.out.println("encrpyted = " + enm);
	      System.out.println("decrypted = " + dem);
	      System.out.println("signatured = " + sim);
	      System.out.println("reverted signature = " + rem);
	      
		  BigInteger msgHashCode= BigInteger.valueOf(m.hashCode());
		  msgHashCode = msgHashCode.abs();
		  BigInteger siMsgHashCode= key.signature(msgHashCode);
		  BigInteger reMsgHasCode = key.revert(siMsgHashCode);

		  System.out.println("Messages Hash Code: " + msgHashCode);
		  System.out.println("Signtured Hash Code: " + siMsgHashCode);
		  System.out.println("Reverted Hash Code: " + reMsgHasCode);
	   }
	}