SENG2250_Assignment3/Q2.java

import java.math.BigInteger;

public class Q2 {

//Setup_Request: Hello

//SETUP: Server's RSA public key

//Client_Hello:IDc

//Server_Hello: IDs , SID

//Ephemeral DH exchange

//Finished, check the shared key

//Data exchange

/**
 * Opens the client and server in seperate terminals
 * @param args
 */
    public static void main(String[] args)
    {
        Q2 system = new Q2();
        system.run();
    }
    
    public void run()
    {
        // try
        // { 
        //  Runtime.getRuntime().exec("cmd /c start cmd.exe /K \"java Q2Server\"");
        //  Thread.sleep(500); //Just to ensure the server has enough time to open
        //  Runtime.getRuntime().exec("cmd /c start cmd.exe /K \"java Q2Client\"");
        // }
        // catch (Exception e)
        // {
        //     e.printStackTrace();
        // }

        Q2RSA rsa = new Q2RSA();
        BigInteger[] publicKey = rsa.getPublicKey();
        BigInteger privateKey = rsa.getPrivateKey();

        BigInteger result1 = encrypt(BigInteger.valueOf(3436), publicKey);
        BigInteger result2 = decrypt(result1, privateKey, publicKey);

    }








    public BigInteger encrypt(BigInteger X, BigInteger[] publicKey)
    {
        return fme(X ,publicKey[1],publicKey[0]);
    }

    public BigInteger decrypt(BigInteger Y, BigInteger privateKey, BigInteger[] publicKey)
    {
        return fme(Y, privateKey, publicKey[0]);
    }


    /**
     * Performs a fast modular exponation, (base^exponent)%modulus.
     * Takes input values as strings containg the numbers
     * @param baseVal
     * @param exponentVal
     * @param modulusVal
     * @return
     */
    public BigInteger fme(BigInteger baseVal, BigInteger exponentVal, BigInteger modulusVal)
    {
        if(modulusVal.equals(BigInteger.valueOf(1)))
        {  
            return BigInteger.valueOf(0);
        }

        BigInteger result = new BigInteger("1");

        while(exponentVal.compareTo(BigInteger.valueOf(0))==1)
        {   
            if(exponentVal.and(BigInteger.valueOf(1)).compareTo(BigInteger.valueOf(1))==0)
            {
                result = result.multiply(baseVal);
                result = result.mod(modulusVal);
            }

            exponentVal = exponentVal.shiftRight(1);
            baseVal = (baseVal.multiply(baseVal)).mod(modulusVal);
        }
        return result;
    }
}