Thread: What is wrong with my code?

Hi,

I'm a beginner and I'm not sure what is wrong with my code or maybe someone can help. I only need to implement code in the very last function (CalculateKey).

Thanks,

import java.math.BigInteger;
 
public class DH_TEST {
 
 
 
	public static void main(String [] args) {
 
		BigInteger q = new BigInteger("353");	// q is a prime number (the modulo)
		BigInteger a = new BigInteger("3");	// a is a primitive root of q (a<q)
 
 
		BigInteger user_A_private = new BigInteger("97");	// private component of User A
		USER userA = new USER(q, a, user_A_private);		// create a the user A
 
 
		BigInteger user_B_private = new BigInteger("233");	// private component of User B
		USER userB = new USER(q, a, user_B_private);		// create the other user
 
 
 
 
 
		BigInteger YB = userB.getPublic();			// Retrieve the public component of user B's key
		userA.OtherUserPublic(YB);				// Store it in user A's instance (need this to calculate our key)
 
 
		BigInteger YA = userA.getPublic();			// Retrieve the public component of user A's key
		userB.OtherUserPublic(YA);				// Store it in user B's instance (need this to calculate our key)
 
 
 
 
 
 
		BigInteger KEY_OF_USER_A = userA.CalculateKey();
		System.out.println("User A's Key: " + KEY_OF_USER_A);
 
 
 
		BigInteger KEY_OF_USER_B = userB.CalculateKey();
		System.out.println("User B's Key: " + KEY_OF_USER_B);
	}
}
 
 
class USER {
	private BigInteger q;		// This is the q (the modulo)
	private BigInteger a;		// this is the a, which is < q
	private BigInteger X;		// our PRIVATE component of the key
	private BigInteger Y;		// our PUBLIC component of the key
 
	private BigInteger Y_otherUser;	// The other user's PUBLIC component of the key
 
 
 
	public USER(BigInteger q, BigInteger a, BigInteger X) {
		this.q = q;
		this.a = a;
		this.X = X;
 
		Y = a.modPow(X,q);	// having a,q, and X, we can calculate Y.
	}
 
 
	public BigInteger getPublic() {
		return Y;
	}
 
 
	public void OtherUserPublic(BigInteger Y_otherUser) {
		this.Y_otherUser = Y_otherUser;
	}
 
 
	public BigInteger CalculateKey(userA, userB) {
 
        userA = Y.modPow(X,q);
 
        return userA;
	}
}

It doesn't compile because you have two parameters but dont tell the compiler what type they are.

public BigInteger CalculateKey(userA, userB) {

You need to tell the compiler what type userA and userB are

example:

public BigInteger CalculateKey(int userA,int userB) {

Welcome to the Forum! Thanks for taking the time to learn to post code correctly. If you haven't already read this topic to learn other useful info for newcomers.

In the future, please give us a hint at the trouble/problem you're trying to solve. If you're getting an error, post it in its entirety.

After adding in the BigInteger type for both userA and userB. Now I'm getting another error about the return (userA, userB);

import java.math.BigInteger;
 
public class DH_TEST {
 
 
 
	public static void main(String [] args) {
 
		BigInteger q = new BigInteger("353");	// q is a prime number (the modulo)
		BigInteger a = new BigInteger("3");	// a is a primitive root of q (a<q)
 
 
		BigInteger user_A_private = new BigInteger("97");	// private component of User A
		USER userA = new USER(q, a, user_A_private);		// create a the user A
 
 
		BigInteger user_B_private = new BigInteger("233");	// private component of User B
		USER userB = new USER(q, a, user_B_private);		// create the other user
 
 
 
 
 
		BigInteger YB = userB.getPublic();			// Retrieve the public component of user B's key
		userA.OtherUserPublic(YB);				// Store it in user A's instance (need this to calculate our key)
 
 
		BigInteger YA = userA.getPublic();			// Retrieve the public component of user A's key
		userB.OtherUserPublic(YA);				// Store it in user B's instance (need this to calculate our key)
 
 
 
 
 
 
		BigInteger KEY_OF_USER_A = userA.CalculateKey();
		System.out.println("User A's Key: " + KEY_OF_USER_A);
 
 
 
		BigInteger KEY_OF_USER_B = userB.CalculateKey();
		System.out.println("User B's Key: " + KEY_OF_USER_B);
	}
}
 
 
class USER {
	private BigInteger q;		// This is the q (the modulo)
	private BigInteger a;		// this is the a, which is < q
	private BigInteger X;		// our PRIVATE component of the key
	private BigInteger Y;		// our PUBLIC component of the key
 
	private BigInteger Y_otherUser;	// The other user's PUBLIC component of the key
 
 
 
	public USER(BigInteger q, BigInteger a, BigInteger X) {
		this.q = q;
		this.a = a;
		this.X = X;
 
		Y = a.modPow(X,q);	// having a,q, and X, we can calculate Y.
	}
 
 
	public BigInteger getPublic() {
		return Y;
	}
 
 
	public void OtherUserPublic(BigInteger Y_otherUser) {
		this.Y_otherUser = Y_otherUser;
	}
 
 
	public BigInteger CalculateKey(BigInteger userA, BigInteger userB) {
 
        userA = Y.modPow(X,q);
        userB = Y.modPow(X,q);
 
        return (userA, userB);
	}
}

There is no need to use two parameters in the method because they are both doing the same thing and don't interact. Just use one and call it twice.

	public BigInteger CalculateKey(BigInteger user) {
 
        user = Y.modPow(X,q);
 
 
        return user;
}

Then call it twice if you want to do the same for two objects:

CalculateKey(usr1);
CalculateKey(usr2);

Now I'm getting another error about the return (userA, userB)

Again, you didn't post the error. Is there a reason?

This is the error I'm getting: (Below in RED)


DH_TEST.java:51: error: method CalculateKey in class USER cannot be applied to g
iven types;
BigInteger KEY_OF_USER_A = userA.CalculateKey();
^
required: BigInteger
found: no arguments
reason: actual and formal argument lists differ in length
DH_TEST.java:58: error: method CalculateKey in class USER cannot be applied to g
iven types;
BigInteger KEY_OF_USER_B = userB.CalculateKey();
^
required: BigInteger
found: no arguments
reason: actual and formal argument lists differ in length
2 errors

import java.math.BigInteger;
 
/**
 *		** Diffie-Hellman **
 * Two parties use a key agreement protocol to generate identical secret keys for 
 * encryption without ever having to transmit the secret key. The protocol works by 
 * both parties agreeing on a set of values (a prime, a base, and a private value) 
 * which are used to generate a key pair.
 */
public class DH_TEST {
 
 
	/**
	 *
	 */
	public static void main(String [] args) {
 
		BigInteger q = new BigInteger("353");	// q is a prime number (the modulo)
		BigInteger a = new BigInteger("3");	// a is a primitive root of q (a<q)
 
 
		BigInteger user_A_private = new BigInteger("97");	// private component of User A
		USER userA = new USER(q, a, user_A_private);		// create a the user A
 
 
		BigInteger user_B_private = new BigInteger("233");	// private component of User B
		USER userB = new USER(q, a, user_B_private);		// create the other user
 
 
 
		//
		// Simulation: Transmit YB and YA to each other
		//
 
		BigInteger YB = userB.getPublic();			// Retrieve the public component of user B's key
		userA.OtherUserPublic(YB);				// Store it in user A's instance (need this to calculate our key)
 
 
		BigInteger YA = userA.getPublic();			// Retrieve the public component of user A's key
		userB.OtherUserPublic(YA);				// Store it in user B's instance (need this to calculate our key)
 
		//
		// Done exchanging data
		//
 
 
 
		//
		// User A calculates the key and displays it.
		//
		BigInteger KEY_OF_USER_A = userA.CalculateKey();
		System.out.println("User A's Key: " + KEY_OF_USER_A);
 
 
		//
		// User A calculates the key and displays it.
		//
		BigInteger KEY_OF_USER_B = userB.CalculateKey();
		System.out.println("User B's Key: " + KEY_OF_USER_B);
	}
}
 
 
/**
 *
 */
class USER {
	private BigInteger q;		// This is the q (the modulo)
	private BigInteger a;		// this is the a, which is < q
	private BigInteger X;		// our PRIVATE component of the key
	private BigInteger Y;		// our PUBLIC component of the key
 
	private BigInteger Y_otherUser;	// The other user's PUBLIC component of the key
 
 
 
	/**
	 * Pass to us the q,a and our PRIVATE component of our key (the X).
	 * We then calculate our PUBLIC component of our key (the Y)
	 */
	public USER(BigInteger q, BigInteger a, BigInteger X) {
		this.q = q;
		this.a = a;
		this.X = X;
 
		Y = a.modPow(X,q);	// having a,q, and X, we can calculate Y.
	}
 
	/**
	 * Returns our PUBLIC component of our key.
	 * The other user will need this to calculate the final secret key.
	 */
	public BigInteger getPublic() {
		return Y;
	}
 
 
	/**
	 * We need to know the other user's PUBLIC component of the key.
	 * Store it so we can use it to calculate our final secret key.
	 */
	public void OtherUserPublic(BigInteger Y_otherUser) {
		this.Y_otherUser = Y_otherUser;
	}
 
	/**
	 * Calculates and returns the SECRET KEY (in the slides this is the K);
	 */
	public BigInteger CalculateKey(BigInteger userA) {
		//
		// *** TO BE IMPLEMENTED ***
		// CALCULATE THE KEY AND RETURN IT
		// NOTE THAT THIS FUNCTION RETURNS A BigInteger Object
		//
        userA = Y.modPow(X,q);
 
        return userA;
	}
}

Re-read the error:

DH_TEST.java:51: error: method CalculateKey in class USER cannot be applied to given types;
BigInteger KEY_OF_USER_A = userA.CalculateKey();
^
required: BigInteger
found: no arguments

Translating: the method CalculateKey() requires a parameter of type BigInteger, but it was called with no arguments.

To fix: call the method with the required parameters.