private void exchangeKeys() { try { output.write(modulus.toByteArray()); byte[] buffer = new byte[ciphertextBlockSize]; input.read(buffer); recipModulus = new BigInteger(1, buffer); } catch (IOException ioe) { System.err.println("Error establishing keys"); } }
// Close socket and IO streams, change appearance/functionality of some components private void closeAll() throws IOException { displayArea.append("\nConnection closing"); output.close(); input.close(); connection.close(); // We are no longer connected connection = null; // Change components serverField.setEditable(true); connectButton.setLabel("Connect to server above"); enterField.setEnabled(false); }
public static void main(String[] args) throws Exception { // prompt user to enter a port number System.out.print("Enter the port number: "); Scanner scan = new Scanner(System.in); int port = scan.nextInt(); scan.nextLine(); System.out.print("Enter the host name: "); String hostName = scan.nextLine(); // Initialize a key pair generator with the SKIP parameters we sepcified, and genrating a pair // This will take a while: 5...15 seconrds System.out.println("Generating a Diffie-Hellman keypair: "); KeyPairGenerator kpg = KeyPairGenerator.getInstance("DH"); kpg.initialize(PARAMETER_SPEC); KeyPair keyPair = kpg.genKeyPair(); System.out.println("key pair has been made..."); // one the key pair has been generated, we want to listen on // a given port for a connection to come in // once we get a connection, we will get two streams, One for input // and one for output // open a port and wait for a connection ServerSocket ss = new ServerSocket(port); System.out.println("Listeining on port " + port + " ..."); Socket socket = ss.accept(); // use to output and input primitive data type DataOutputStream out = new DataOutputStream(socket.getOutputStream()); // next thing to do is send our public key and receive client's // this corresponds to server step 3 and step 4 in the diagram System.out.println("Sending my public key..."); byte[] keyBytes = keyPair.getPublic().getEncoded(); out.writeInt(keyBytes.length); out.write(keyBytes); System.out.println("Server public key bytes: " + CryptoUtils.toHex(keyBytes)); // receive the client's public key System.out.println("Receiving client's public key..."); DataInputStream in = new DataInputStream(socket.getInputStream()); keyBytes = new byte[in.readInt()]; in.readFully(keyBytes); // create client's public key KeyFactory kf = KeyFactory.getInstance("DH"); X509EncodedKeySpec x509Spec = new X509EncodedKeySpec(keyBytes); PublicKey clientPublicKey = kf.generatePublic(x509Spec); // print out client's public key bytes System.out.println( "Client public key bytes: " + CryptoUtils.toHex(clientPublicKey.getEncoded())); // we can now use the client's public key and // our own private key to perform the key agreement System.out.println("Performing the key agreement ... "); KeyAgreement ka = KeyAgreement.getInstance("DH"); ka.init(keyPair.getPrivate()); ka.doPhase(clientPublicKey, true); // in a chat application, each character is sendt over the wire, separetly encrypted, // Instead of using ECB, we are goin to use CFB, with a block size of 8 bits(1byte) // to send each character. We will encrypt the same character in a different way // each time. But in order to use CFB8, we need an IVof 8 bytes. We will create // that IV randomly and and send it to the client. It doesn't matter if somoene // eavesdrops on the IV when it is sent over the wire. it's not sensitive info // creating the IV and sending it corresponds to step 6 and 7 byte[] iv = new byte[8]; SecureRandom sr = new SecureRandom(); sr.nextBytes(iv); out.write(iv); // we generate the secret byte array we share with the client and use it // to create the session key (Step 8) byte[] sessionKeyBytes = ka.generateSecret(); // create the session key SecretKeyFactory skf = SecretKeyFactory.getInstance("DESede"); DESedeKeySpec DESedeSpec = new DESedeKeySpec(sessionKeyBytes); SecretKey sessionKey = skf.generateSecret(DESedeSpec); // printout session key bytes System.out.println("Session key bytes: " + CryptoUtils.toHex(sessionKey.getEncoded())); // now use tha that session key and IV to create a CipherInputStream. We will use them to read // all character // that are sent to us by the client System.out.println("Creating the cipher stream ..."); Cipher decrypter = Cipher.getInstance("DESede/CFB8/NoPadding"); IvParameterSpec spec = new IvParameterSpec(iv); decrypter.init(Cipher.DECRYPT_MODE, sessionKey, spec); CipherInputStream cipherIn = new CipherInputStream(socket.getInputStream(), decrypter); // we just keep reading the input and print int to the screen, until -1 sent over int theCharacter = 0; theCharacter = cipherIn.read(); while (theCharacter != -1) { System.out.print((char) theCharacter); theCharacter = cipherIn.read(); } // once -1 is received we want to close up our stream and exit cipherIn.close(); in.close(); out.close(); socket.close(); }
public void actionPerformed(ActionEvent e) { Object source = e.getSource(); // Client pressed enter in the message entry field-send it if (source == enterField) { // Get the message message = e.getActionCommand(); try { // Encipher the message if (message.length() > plaintextBlockSize) message = message.substring(0, plaintextBlockSize); byte[] ciphertext = Ciphers.RSAEncipherWSalt(message.getBytes(), BigIntegerMath.THREE, recipModulus, sr); // Send to the server output.write(ciphertext); output.flush(); // Display same message in client output area displayArea.append("\n" + message); enterField.setText(""); } catch (IOException ioe) { displayArea.append("\nError writing message"); } } else if (source == connectButton) { if (connection != null) { // Already connected-button press now means disconnect try { // Send final message of 0 byte[] lastMsg = new byte[1]; lastMsg[0] = 0; output.write(Ciphers.RSAEncipherWSalt(lastMsg, BigIntegerMath.THREE, recipModulus, sr)); output.flush(); // close connection and IO streams, change some components closeAll(); } catch (IOException ioe) { displayArea.append("\nError closing connection"); } } else { // Not connected-connect // Get name of server to connect to chatServer = serverField.getText(); displayArea.setText("Attempting connection to " + chatServer); try { // Set up the socket connection = new Socket(chatServer, 55555); displayArea.append("\nConnected to: " + connection.getInetAddress().getHostName()); // Set up the IO streams output = new DataOutputStream(connection.getOutputStream()); output.flush(); input = new DataInputStream(connection.getInputStream()); // Exchange public keys with the server-send yours, get theirs exchangeKeys(); // Change appearance/functionality of some components serverField.setEditable(false); connectButton.setLabel("Disconnect from server above"); enterField.setEnabled(true); // Set up a thread to listen for the connection listener = new Thread( new Runnable() { public void run() { go(); } }); listener.start(); } catch (IOException ioe) { displayArea.append("\nError connecting to " + chatServer); } } } }