// internal implementation of translateKey() for public keys. See JCA doc private PublicKey translatePublicKey(PublicKey key) throws InvalidKeyException { if (key instanceof RSAPublicKey) { if (key instanceof RSAPublicKeyImpl) { return key; } RSAPublicKey rsaKey = (RSAPublicKey) key; try { return new RSAPublicKeyImpl(rsaKey.getModulus(), rsaKey.getPublicExponent()); } catch (RuntimeException e) { // catch providers that incorrectly implement RSAPublicKey throw new InvalidKeyException("Invalid key", e); } } else if ("X.509".equals(key.getFormat())) { byte[] encoded = key.getEncoded(); return new RSAPublicKeyImpl(encoded); } else { throw new InvalidKeyException( "Public keys must be instance " + "of RSAPublicKey or have X.509 encoding"); } }
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(); }