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();
  }
Esempio n. 2
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  public static void main(String[] args) {
    try {
      if (args[0].equals("-genkey")) {
        KeyPairGenerator pairgen = KeyPairGenerator.getInstance("RSA");
        SecureRandom random = new SecureRandom();
        pairgen.initialize(KEYSIZE, random);
        KeyPair keyPair = pairgen.generateKeyPair();
        ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(args[1]));
        out.writeObject(keyPair.getPublic());
        out.close();
        out = new ObjectOutputStream(new FileOutputStream(args[2]));
        out.writeObject(keyPair.getPrivate());
        out.close();
      } else if (args[0].equals("-encrypt")) {
        KeyGenerator keygen = KeyGenerator.getInstance("AES");
        SecureRandom random = new SecureRandom();
        keygen.init(random);
        SecretKey key = keygen.generateKey();

        // wrap with RSA public key
        ObjectInputStream keyIn = new ObjectInputStream(new FileInputStream(args[3]));
        Key publicKey = (Key) keyIn.readObject();
        keyIn.close();

        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.WRAP_MODE, publicKey);
        byte[] wrappedKey = cipher.wrap(key);
        DataOutputStream out = new DataOutputStream(new FileOutputStream(args[2]));
        out.writeInt(wrappedKey.length);
        out.write(wrappedKey);

        InputStream in = new FileInputStream(args[1]);
        cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, key);
        crypt(in, out, cipher);
        in.close();
        out.close();
      } else {
        DataInputStream in = new DataInputStream(new FileInputStream(args[1]));
        int length = in.readInt();
        byte[] wrappedKey = new byte[length];
        in.read(wrappedKey, 0, length);

        // unwrap with RSA private key
        ObjectInputStream keyIn = new ObjectInputStream(new FileInputStream(args[3]));
        Key privateKey = (Key) keyIn.readObject();
        keyIn.close();

        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.UNWRAP_MODE, privateKey);
        Key key = cipher.unwrap(wrappedKey, "AES", Cipher.SECRET_KEY);

        OutputStream out = new FileOutputStream(args[2]);
        cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, key);

        crypt(in, out, cipher);
        in.close();
        out.close();
      }
    } catch (IOException e) {
      e.printStackTrace();
    } catch (GeneralSecurityException e) {
      e.printStackTrace();
    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    }
  }