ORIGINAL RSA IMPLEMENTATION IN JAVA

HEY,this is  implementation of original RSA algorithm .

RSA is an algorithm used by modern computers to encrypt and decrypt messages. It is an asymmetric cryptographic algorithm. Asymmetric means that there are two different keys. This is also called public key cryptography, because one of them can be given to everyone.

For reference visit RSA_(cryptosystem)

import java.math.BigInteger;

import java.security.SecureRandom;

public class RSA {

  private BigInteger n, d, e;

  private int bitlen = 1024;

  /** Create an instance that can encrypt using someone elses public key. */

  public RSA(BigInteger newn, BigInteger newe) {

    n = newn;

    e = newe;

  }

  /** Create an instance that can both encrypt and decrypt. */

  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);

  }

  /** Encrypt the given plaintext message. */

  public synchronized String encrypt(String message) {

    return (new BigInteger(message.getBytes())).modPow(e, n).toString();

  }

  /** Encrypt the given plaintext message. */

  public synchronized BigInteger encrypt(BigInteger message) {

    return message.modPow(e, n);

  }

  /** Decrypt the given ciphertext message. */

  public synchronized String decrypt(String message) {

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

  }

  /** Decrypt the given ciphertext message. */

  public synchronized BigInteger decrypt(BigInteger message) {

    return message.modPow(d, n);

  }

  /** Generate a new public and private key set. */

  public synchronized void generateKeys() {

    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);

  }

  /** Return the modulus. */

  public synchronized BigInteger getN() {

    return n;

  }

  /** Return the public key. */

  public synchronized BigInteger getE() {

    return e;

  }

  /** Trivial test program. */

  public static void main(String[] args) {

    RSA rsa = new RSA(1024);

    String text1 = "Yellow and Black Border Collies";

    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);

  }

}