RSA

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```package com.thealgorithms.ciphers;

import java.math.BigInteger;
import java.security.SecureRandom;

/**
* @author Nguyen Duy Tiep on 23-Oct-17.
*/
public class RSA {

private BigInteger modulus;
private BigInteger privateKey;
private BigInteger publicKey;

public RSA(int bits) {
generateKeys(bits);
}

/**
* @return encrypted message
*/
public synchronized String encrypt(String message) {
return (new BigInteger(message.getBytes())).modPow(publicKey, modulus).toString();
}

/**
* @return encrypted message as big integer
*/
public synchronized BigInteger encrypt(BigInteger message) {
return message.modPow(publicKey, modulus);
}

/**
* @return plain message
*/
public synchronized String decrypt(String encryptedMessage) {
return new String((new BigInteger(encryptedMessage)).modPow(privateKey, modulus).toByteArray());
}

/**
* @return plain message as big integer
*/
public synchronized BigInteger decrypt(BigInteger encryptedMessage) {
return encryptedMessage.modPow(privateKey, modulus);
}

/**
* Generate a new public and private key set.
*/
public final synchronized void generateKeys(int bits) {
SecureRandom r = new SecureRandom();
BigInteger p = new BigInteger(bits / 2, 100, r);
BigInteger q = new BigInteger(bits / 2, 100, r);
modulus = p.multiply(q);

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

publicKey = BigInteger.valueOf(3L);

while (m.gcd(publicKey).intValue() > 1) {