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How to Handle Exceptions in Java's AES Encryption Method?

Dec 17, 2024 am 06:25 AM

How to Handle Exceptions in Java's AES Encryption Method?

Exception Handling in Java Code

Consider the following Java code snippet:

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.security.*;
import java.io.*;


public class EncryptURL extends JApplet implements ActionListener {

    // ...

    public void encrypt(String toEncrypt) throws Exception {
        try {
            String plaintext = toEncrypt;
            String key = "01234567890abcde";
            String iv = "fedcba9876543210";

            SecretKeySpec keyspec = new SecretKeySpec(key.getBytes(), "AES");
            IvParameterSpec ivspec = new IvParameterSpec(iv.getBytes());

            Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
            cipher.init(Cipher.ENCRYPT_MODE, keyspec, ivspec);
            byte[] encrypted = cipher.doFinal(toEncrypt.getBytes());

            return encrypted;
        }
        catch(Exception e) {
            return null; // Always must return something
        }
    }


    public void actionPerformed(ActionEvent e) {
        if (e.getActionCommand() == "Submit") {

            // ...

            String concatURL =
                "user=" + subUserName + "&f=" + subFName +
                "&l=" + subLName + "&em=" + subEmail +
                "&p=" + subPhone + "&h=" + subHeartbeatID +
                "&re=" + subRegionCode + "&ret=" + subRetRegionCode;

            // ...

            try {
                byte[] encrypted = encrypt(concatURL);
                String encryptedString = bytesToHex(encrypted);
                // ...
            } catch (Exception exc) {
                // TODO: handle exception
            }
        }
    }

    // ...

}
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The following questions and answers address the problems faced while compiling this code snippet.

Question 1: Why does the code snippet throw an "Exception; must be caught or declared to be thrown" exception when trying to compile it?

Answer:

This exception occurs because the encrypt method is declared to throw an Exception but does not handle it in its try-catch block. To resolve this, a catch block has been added to the encrypt method to handle the Exception.

Question 2: Why does the code snippet throw a "missing return statement" exception for line 109?

Answer:

The encrypt method has a declared return type of byte[], which means it must return a value of that type in all cases. The original code did not have a return statement in the catch block, resulting in an exception. A return statement has been added to the catch block to return null in case of an exception.

Lessons Learned:

  1. A method with a return type must always return an object of that type in all possible scenarios.
  2. All checked exceptions must always be handled.

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