Implementation of RSA Algorithm(Encryption and Decryption) in Java

JAVA Program

import java.math.BigInteger;



import java.util.Random;



import java.io.*;



public class RSA {



 private BigInteger p;



 private BigInteger q;



 private BigInteger N;



 private BigInteger phi;



 private BigInteger e;



 private BigInteger d;



 private int bitlength = 1024;



 private int blocksize = 256;



 //blocksize in byte



 private Random r;



 public RSA() {



  r = new Random();



  p = BigInteger.probablePrime(bitlength, r);



  q = BigInteger.probablePrime(bitlength, r);



  N = p.multiply(q);



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



  e = BigInteger.probablePrime(bitlength/2, r);



  while (phi.gcd(e).compareTo(BigInteger.ONE) > 0 && e.compareTo(phi) < 0 ) {



   e.add(BigInteger.ONE);



  }



  d = e.modInverse(phi);



 }



 public RSA(BigInteger e, BigInteger d, BigInteger N) {



  this.e = e;



  this.d = d;



  this.N = N;



 }



 public static void main (String[] args) throws IOException {



  RSA rsa = new RSA();



  DataInputStream in=new DataInputStream(System.in);



  String teststring ;



  System.out.println("Enter the plain text:");



  teststring=in.readLine();



  System.out.println("Encrypting String: " + teststring);



  System.out.println("String in Bytes: " + bytesToString(teststring.getBytes()));



  // encrypt



  byte[] encrypted = rsa.encrypt(teststring.getBytes());



  System.out.println("Encrypted String in Bytes: " + bytesToString(encrypted));



  // decrypt



  byte[] decrypted = rsa.decrypt(encrypted);



  System.out.println("Decrypted String in Bytes: " +  bytesToString(decrypted));



  System.out.println("Decrypted String: " + new String(decrypted));



 }



 private static String bytesToString(byte[] encrypted) {



  String test = "";



  for (byte b : encrypted) {



   test += Byte.toString(b);



  }



  return test;



 }



 //Encrypt message



 public byte[] encrypt(byte[] message) {



  return (new BigInteger(message)).modPow(e, N).toByteArray();



 }



 // Decrypt message



 public byte[] decrypt(byte[] message) {



  return (new BigInteger(message)).modPow(d, N).toByteArray();



 }



}