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src/DiffieHellman.java
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src/DiffieHellman.java
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/*
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* FileTrans 1.0
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* Copyright © 2017 Ben Goldsworthy (rumperuu)
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*
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* A program to securely receive a file.
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*
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* This file is part of FileTrans.
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*
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* FileTrans is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* FileTrans is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with FileTrans. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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** This class represents a client program for interfacing with an
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** already-running instance of the server program.
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**/
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import java.io.*;
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import java.math.BigInteger;
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import java.net.*;
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import java.security.*;
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import java.util.*;
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import java.util.regex.*;
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import javax.crypto.*;
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import javax.crypto.spec.*;
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/**
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** @author Ben Goldsworthy (rumperuu) <me+filetrans@bengoldsworthy.net>
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** @version 1.0
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**/
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public class DiffieHellman {
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private static String ip = "";
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private static int port = 0;
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private static BigInteger p = null, g = null;
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private static int a = 0;
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/**
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** Main function. Receives and validates arguments, then actives
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** cracker threads.
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**
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** @param args The arguments passed to the program at the
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** command-line.
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**/
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public static void main(String[] args) {
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// Quits with error if insufficent number of arguments passed at
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// command-line.
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if (args.length == 5) {
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parseArgs(args);
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try {
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// Connects to the server and sets up I/O.
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InetAddress addr = InetAddress.getByName(ip);
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Socket socket = new Socket(addr, port);
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System.out.println("Socket: " + socket);
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BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
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PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())),true);
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// Performs the Diffie-Hellman key exchange protocol with the
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// server.
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out.println("##DHA##" + (g.pow(a).mod(p)) + "####");
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String B = parseResp(in.readLine());
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BigInteger s = new BigInteger(B).pow(a).mod(p);
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System.out.println("Shared Diffie-Hellman key: " + s);
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// Generates a nonce...
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String R = Double.toString(Math.floor(Math.random() * 9000 + 1000)).replaceAll(".0", "");
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// ...converts the D-H shared key into the hash string...
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String DH = s.toString();
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String DHKey = "";
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for (int i = 0; i < (12 - DH.length()); i++) { DHKey = DHKey + "0"; }
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String nonce = R + DHKey + DH;
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System.out.println("RDH: "+nonce);
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// ...and generates the 128-bit session key by hashing the
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// hash string and truncating it to the first 16 bytes.
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MessageDigest digest = MessageDigest.getInstance("SHA-256");
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byte[] sessionKey = digest.digest(nonce.getBytes("UTF-8"));
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sessionKey = Arrays.copyOfRange(sessionKey, 0, sessionKey.length/2);
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// Finally, sends nonce to the server.
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out.println("##NONCE##"+R+"####");
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// Requests the file from the server...
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out.println("##REQFILE####");
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String encodedFile = parseResp(in.readLine());
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System.out.println("File received: " +encodedFile);
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// ...decodes it from Base64...
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byte[] decodedFile = Base64.getDecoder().decode(encodedFile);
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// ...and decrypts it.
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Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
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SecretKeySpec key = new SecretKeySpec(sessionKey, "AES");
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IvParameterSpec iv = new IvParameterSpec(nonce.getBytes());
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cipher.init(Cipher.DECRYPT_MODE, key, iv);
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String decryptedFile = new String(cipher.doFinal(decodedFile));//.substring(10);
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// Computes the hash of the file content...
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byte[] fileHash = digest.digest(decryptedFile.split(":", 2)[1].getBytes());
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// ...encrypts the hash with the session key...
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cipher.init(Cipher.ENCRYPT_MODE, key, iv);
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byte[] encryptedHash = cipher.doFinal(fileHash);
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// ...and returns it to the server for verification.
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String encodedHash = Base64.getEncoder().encodeToString(encryptedHash);
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System.out.println("Verifying hash: " + encodedHash);
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out.println("##VERIFY##"+encodedHash+"####");
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System.out.println(in.readLine());
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System.out.println(decryptedFile);
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socket.close();
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} catch (java.io.IOException e) {
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System.out.println("Can't connect to " + args[0]);
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System.out.println(e);
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} catch (NoSuchAlgorithmException | NoSuchPaddingException e) {
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// TODO Auto-generated catch block
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e.printStackTrace();
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} catch (InvalidKeyException e) {
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// TODO Auto-generated catch block
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e.printStackTrace();
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} catch (IllegalBlockSizeException e) {
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// TODO Auto-generated catch block
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e.printStackTrace();
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} catch (BadPaddingException e) {
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// TODO Auto-generated catch block
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e.printStackTrace();
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} catch (InvalidAlgorithmParameterException e) {
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// TODO Auto-generated catch block
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e.printStackTrace();
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}
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} else {
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System.out.println("Invalid number of arguments. Program should be run with the following arguments:");
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System.out.println("\tdh.jar <ip> <port> <p> <g> <secret number>");
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System.exit(1);
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}
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}
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/**
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** Parses the arguments passed to the program to ensure they are
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** valid.
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**/
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private static void parseArgs(String[] args) {
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ip = args[0];
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if (!isIP(ip)) {
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System.err.println("Invalid format of argument "+ip+": argument must be an IP address.");
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System.exit(1);
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}
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ip = args[0];
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try {
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port = Integer.parseInt(args[1]);
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p = new BigInteger(args[2]);
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g = new BigInteger(args[3]);
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a = Integer.parseInt(args[4]);
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} catch (NumberFormatException e) {
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System.err.println("Invalid format of argument: argument must be an integer.");
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System.exit(1);
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}
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}
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/**
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** Tests that the passed IP address is of a valid format.
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**/
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private static boolean isIP(String ip) {
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// Source for IP address RegEx: https://www.mkyong.com/regular-expressions/how-to-validate-ip-address-with-regular-expression/
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final String IPADDRESS_PATTERN =
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"^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
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"([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
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"([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
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"([01]?\\d\\d?|2[0-4]\\d|25[0-5])$";
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Pattern pattern = Pattern.compile(IPADDRESS_PATTERN);
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Matcher matcher;
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return Pattern.compile(IPADDRESS_PATTERN).matcher(ip).matches();
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}
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/**
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** Extracts the data from the sent file.
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**/
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private static String parseResp(String resp) {
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return resp.replaceAll("##[A-Z]+##([^#]+)####", "$1");
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}
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}
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