Practical No-6

AIM- Write a program to implement RSA algorithm in Java

import java.math.BigInteger;

import java.security.SecureRandom;

public class rsa

{

            private BigInteger n, d, e;

             private int bitlen = 1024;

              public rsa(BigInteger newn, BigInteger newe)

             {

                        n = newn;

                        e = newe;

            }

 public rsa(int bits)

{

                        bitlen = bits;

                        SecureRandom r = new SecureRandom();

                        BigInteger p = new BigInteger(bitlen / 2, 100, r);

                          BigInteger q = new BigInteger(bitlen / 2, 100, r);

                         n = p.multiply(q);

                        BigInteger m = (p.subtract(BigInteger.ONE)).multiply(q.subtract(BigInteger.ONE));

                        e = new BigInteger("3");

  while (m.gcd(e).intValue() > 1)

 {

                                     e = e.add(new BigInteger("2"));

                        }

                         d = e.modInverse(m);

             }

public synchronized BigInteger encrypt(BigInteger message)

 {

                         return message.modPow(e, n);

            }

 public synchronized BigInteger decrypt(BigInteger message)

{

                        return message.modPow(d, n);

}

public static void main(String[] args)

{

                         rsa rsa = new rsa(1024);

                        String text1 = "SERO";

                         System.out.println("Plaintext: " + text1);

                        BigInteger plaintext = new BigInteger(text1.getBytes());

                        BigInteger ciphertext = rsa.encrypt(plaintext);

                         System.out.println("Ciphertext: " + ciphertext);

                          plaintext = rsa.decrypt(ciphertext);

                           String text2 = new String(plaintext.toByteArray());

                         System.out.println("Plaintext: " + text2);

             }

}