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package RSAkeamanansistem;
import java.io.DataInputStream;

import java.io.IOException;

import java.math.BigInteger;

import java.util.Random;
/**
 *
 * @author meciwp
 */
public class RSAKeamananSistem

{

    private BigInteger a;

    private BigInteger b;

    private BigInteger D;

    private BigInteger phi;

    private BigInteger f;

    private BigInteger g;

    private int        bitlength = 724;

    private Random     R;



    public RSAKeamananSistem()

    {

        R = new Random();

        a = BigInteger.probablePrime(bitlength, R);

        b = BigInteger.probablePrime(bitlength, R);

        D = a.multiply(b);

        phi = a.subtract(BigInteger.ONE).multiply(b.subtract(BigInteger.ONE));

        f = BigInteger.probablePrime(bitlength / 2, R);

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

        {

            f.add(BigInteger.ONE);

        }

        g = f.modInverse(phi);

    }



    public RSAKeamananSistem(BigInteger f, BigInteger g, BigInteger D)

    {

        this.f = f;

        this.g = g;

        this.D = D;

    }



    @SuppressWarnings("deprecation")

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

    {

        RSAKeamananSistem rsa = new RSAKeamananSistem();

        DataInputStream in = new DataInputStream(System.in);

        String teststring;

        System.out.println("Masukan kata yang Akan di Enkripsi:");

        teststring = in.readLine();

        System.out.println("Kata Yang Anda Masukan Adalah: " + teststring);

        System.out.println("String in Bytes: "

                + bytesToString(teststring.getBytes()));

        // encrypt

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

        // decrypt

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

        System.out.println("Decrypting 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(f, D).toByteArray();

    }



    // Decrypt message

    public byte[] decrypt(byte[] message)

    {

        return (new BigInteger(message)).modPow(g, D).toByteArray();

    }

}