import java.io.*; import java.math.BigInteger; import java.net.*; import java.security.SecureRandom; import java.util.Random; public class RSA_Client { private static final String HOST = "localhost"; private static final int PORT = 12345; // Converts a string message to its numerical representation private static BigInteger msgToNumber(String message) { StringBuilder numberRepresentation = new StringBuilder(); for (char c : message.toCharArray()) { int numericValue = c - 'A' + 1; // Converts A=1, B=2, ..., Z=26 numberRepresentation.append(numericValue); } return new BigInteger(numberRepresentation.toString()); } public static void main(String[] args) throws Exception { try (Socket socket = new Socket(HOST, PORT); ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream()); ObjectInputStream in = new ObjectInputStream(socket.getInputStream())) { System.out.println("Connected to server."); // Receive public key from the server BigInteger e = (BigInteger) in.readObject(); BigInteger n = (BigInteger) in.readObject(); System.out.println("Public key received: (e = " + e + ", n = " + n + ")"); // Message to send String message = "HI"; System.out.println("Original message: " + message); // Convert the message to a numerical value BigInteger plaintext = msgToNumber(message); // Encrypt the message BigInteger encryptedMessage = plaintext.modPow(e, n); System.out.println("Encrypted message: " + encryptedMessage); // Send encrypted message to the server out.writeObject(encryptedMessage); // Receive response from the server String response = (String) in.readObject(); System.out.println("Response from server: " + response); } } }