Prompt Title: File Structure Mini Projects

Certainly! Here's an example of Java code for a simple secure file transfer system that encrypts files during the transfer process. This code assumes the use of AES encryption algorithm and Java's built-in libraries for encryption and network communication.

javaCopy code
import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;
import javax.net.ssl.SSLSocket;
import javax.net.ssl.SSLSocketFactory;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.security.spec.KeySpec;

public class SecureFileTransferSystem {
    private static final String ALGORITHM = "AES";
    private static final String TRANSFORMATION = "AES/ECB/PKCS5Padding";
    private static final String SECRET_KEY = "YourSecretKey";

    public static void main(String[] args) {
        // Start the server
        Thread serverThread = new Thread(() -> startServer());
        serverThread.start();

        // Upload a file as a client
        uploadFile("path/to/file.txt", "localhost", 8888);
    }

    private static void startServer() {
        try {
            ServerSocket serverSocket = new ServerSocket(8888);
            System.out.println("Server started. Waiting for connections...");

            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("Client connected: " + socket.getInetAddress());

                // Handle client connection in a separate thread
                Thread clientThread = new Thread(() -> handleClient(socket));
                clientThread.start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void handleClient(Socket socket) {
        try {
            // Receive the encrypted file from the client
            InputStream inputStream = socket.getInputStream();
            FileOutputStream fileOutputStream = new FileOutputStream("path/to/destination/file.txt");
            decryptFile(inputStream, fileOutputStream);

            // Close streams and socket
            fileOutputStream.close();
            inputStream.close();
            socket.close();

            System.out.println("File received and decrypted successfully.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void uploadFile(String filePath, String serverHost, int serverPort) {
        try {
            // Create a SSL socket and connect to the server
            SSLSocketFactory sslSocketFactory = (SSLSocketFactory) SSLSocketFactory.getDefault();
            SSLSocket sslSocket = (SSLSocket) sslSocketFactory.createSocket(serverHost, serverPort);
            System.out.println("Connected to server: " + sslSocket.getInetAddress());

            // Send the file to the server
            OutputStream outputStream = sslSocket.getOutputStream();
            FileInputStream fileInputStream = new FileInputStream(filePath);
            encryptFile(fileInputStream, outputStream);

            // Close streams and socket
            outputStream.close();
            fileInputStream.close();
            sslSocket.close();

            System.out.println("File uploaded and encrypted successfully.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void encryptFile(InputStream inputStream, OutputStream outputStream) throws IOException {
        try {
            SecretKeySpec secretKeySpec = generateSecretKey();
            Cipher cipher = Cipher.getInstance(TRANSFORMATION);
            cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec);

            // Encrypt and write the file in chunks
            byte[] buffer = new byte[8192];
            int bytesRead;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                byte[] encryptedBytes = cipher.update(buffer, 0, bytesRead);
                outputStream.write(encryptedBytes);
            }
            byte[] finalBytes = cipher.doFinal();
            outputStream.write(finalBytes);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private