rsa

import java.util.Scanner;
import java.io.IOException;
import java.math.BigInteger;
import java.util.Random;
public class RSA_algorithm
{
    public static void main(String[] args)//main method
    {
    	BigInteger p,q,n,z,e,d;
 		byte[] encrypted,decrypted =new byte[1000];
    	 	int range=128;
        Random random = new Random();
	    p = BigInteger.probablePrime(range, random);//find p randomly
        q = BigInteger.probablePrime(range, random);//find q randomly
        e = BigInteger.probablePrime(range, random);//find e randomly
        n = p.multiply(q);//n=p * q
        z = p.subtract(BigInteger.ONE).multiply(q.subtract(BigInteger.ONE));//z=(p-q)*(q-1)
        while (e.gcd(z).compareTo(BigInteger.ONE) > 0 && e.compareTo(z) < 0)//find e such that e & z are relatively prime
        {
            e = e.add(BigInteger.ONE);
        }
        d = e.modInverse(z);//find d such that (d*e)mod z=1
        long d1 = d.longValue();
        long n1 = n.longValue();
        System.out.println("d : "+Long.toHexString(d1) +"\nn : "+Long.toHexString(n1));//Print d and n
        Scanner in = new Scanner(System.in);
        System.out.println("Enter the Text:");//enter original text
        String text = in.nextLine();
        encrypted = encrypt_decrypt(text.getBytes(),e,n,true);//encrypt by passing original keyword,e,n
        decrypted = encrypt_decrypt(encrypted,d,n,false);//decrypt by passing cipher text,d,n
        System.out.println("Decrypted String: " + new String(decrypted));//Word after decryption
    }

    public static byte[] encrypt_decrypt(byte[] message,BigInteger e, BigInteger n,boolean t)    // Encrypt/decrypt method
    {
    		BigInteger c=new BigInteger(message).modPow(e,n);//encrypt/decrypt
    		if(t) {
			long n1 = c.longValue();
			String hex = Long.toHexString(n1);
    			System.out.println("Cipher Text : "+hex);//print cipher text
    		}
    		return c.toByteArray();//BigInteger to byte array conversion with return
    }
}