How to use Socket stream in two other types of Streams - Java

Question

I'm trying to implement Diffie-Hellman's handshake for Java. I have a small problem, the Diffie-Hellman is done using DataInputStream and DataOutputStream with the client's Socket, but in order to use the secret it returns, I need to use a CipherStream. So I'm using a CipherStream and a DataStream over the socket.

public byte[] DHHandshake(Socket s){
        byte[] secret = null;
        try (DataOutputStream out = new DataOutputStream(s.getOutputStream())){
            try(DataInputStream in = new DataInputStream(s.getInputStream())){
                //Crear llave pública y privada en el cliente.
                KeyPairGenerator kpg = KeyPairGenerator.getInstance(PROTOCOL);
                kpg.initialize(Skip.sDHparameterSpec);
                KeyPair keyPair = kpg.generateKeyPair();

                //Envía llave pública del cliente al servidor
                byte[] keyBytes = keyPair.getPublic().getEncoded();
                out.writeInt(keyBytes.length);
                out.write(keyBytes);

                //Recibe llave pública del servidor
                keyBytes = new byte[in.readInt()];
                in.readFully(keyBytes);
                KeyFactory kf = KeyFactory.getInstance(PROTOCOL);
                X509EncodedKeySpec x509Spec = new X509EncodedKeySpec(keyBytes);
                PublicKey theirPublicKey = kf.generatePublic(x509Spec);

                //Llave pública servidor + llave privada cliente = llave compartida.
                KeyAgreement ka = KeyAgreement.getInstance(PROTOCOL) ;
                ka.init(keyPair.getPrivate());
                ka.doPhase(theirPublicKey, true);
                secret = ka.generateSecret();
            }
        }catch(Exception e) {
            e.printStackTrace();
        }
        return secret;
    }

The try-with-resources closes the Data Streams BUT ALSO closes the Socket. So when I try to send the file with a CipherStream using the secret returned in DiffieHellman, it throws an Exception saying the socket is closed:

private void receiveFile(Socket s, byte[] secret){
        try(FileOutputStream fileWriter = new FileOutputStream(FILE)){
            Cipher cipher = Cipher.getInstance(ALGORITHM + "/ECB/PKCS5PADDING");
            SecretKeySpec keySpec = new SecretKeySpec(secret, ALGORITHM); 
            cipher.init(Cipher.DECRYPT_MODE, keySpec);
            try(CipherInputStream cipherIn = new CipherInputStream(s.getInputStream(), cipher)){
                byte[] fileBuffer = new byte[1024];
                int len;
                while ((len = cipherIn.read(fileBuffer)) >= 0)
                    fileWriter.write(fileBuffer, 0, len);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } 
        //TODO checkMD5
    }

So here are my questions:

• If I don't close the DataStream then is it possible to re-use the SocketStream to send data. Wouldn't this damage the SocketStream because the DataStream and CipherStream are using it at the same time?

• Is there a way to close the DataStream without closeing the SocketStream?

• Is there a way to initialize the CipherStream using the DataStream? Like reusing it?

Answer 1

The simple answer to all of this is to wrap the cipher streams around the respective data streams.