public void run() {
try {
ObjectInputStream ois = new ObjectInputStream(s.getInputStream());
ObjectOutputStream oos = new ObjectOutputStream(s.getOutputStream());
BigInteger bg = dhSpec.getG();
BigInteger bp = dhSpec.getP();
oos.writeObject(bg);
oos.writeObject(bp);
KeyPairGenerator kpg = KeyPairGenerator.getInstance("DH");
kpg.initialize(1024);
KeyPair kpa = (KeyPair) ois.readObject();
KeyAgreement dh = KeyAgreement.getInstance("DH");
KeyPair kp = kpg.generateKeyPair();
oos.writeObject(kp);
dh.init(kp.getPrivate());
Key pk = dh.doPhase(kpa.getPublic(), true);
MessageDigest sha256 = MessageDigest.getInstance("SHA-256");
byte[] rawbits = sha256.digest(dh.generateSecret());
Cipher c = Cipher.getInstance(CIPHER_MODE);
SecretKey key = new SecretKeySpec(rawbits, 0, 16, "AES");
byte ivbits[] = (byte[]) ois.readObject();
IvParameterSpec iv = new IvParameterSpec(ivbits);
c.init(Cipher.DECRYPT_MODE, key, iv);
Mac m = Mac.getInstance("HmacSHA1");
SecretKey mackey = new SecretKeySpec(rawbits, 16, 16, "HmacSHA1");
m.init(mackey);
byte ciphertext[], cleartext[], mac[];
try {
while (true) {
ciphertext = (byte[]) ois.readObject();
mac = (byte[]) ois.readObject();
if (Arrays.equals(mac, m.doFinal(ciphertext))) {
cleartext = c.update(ciphertext);
System.out.println(ct + " : " + new String(cleartext, "UTF-8"));
} else {
// System.exit(1);
System.out.println(ct + "error");
}
}
} catch (EOFException e) {
cleartext = c.doFinal();
System.out.println(ct + " : " + new String(cleartext, "UTF-8"));
System.out.println("[" + ct + "]");
} finally {
if (ois != null) ois.close();
if (oos != null) oos.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
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();
}
