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);
}
}
}
}
