Implementation of RSA algorithm in java

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;// In Bytes
        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()));

// encryption

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

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

// decryption

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;

}

//Method to Encrypt message

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

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

}

//  Method to Decrypt message

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

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

}

}