StealthServlet.java Source code

Introduction

Here is the source code for StealthServlet.java

Source

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.bouncycastle.crypto.StreamCipher;
import org.bouncycastle.crypto.engines.RC4Engine;
import org.bouncycastle.crypto.params.KeyParameter;

public class StealthServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String user = request.getParameter("user");

        HttpSession session = request.getSession();
        StreamCipher inCipher = (StreamCipher) session.getAttribute("inCipher");
        StreamCipher outCipher = (StreamCipher) session.getAttribute("outCipher");
        if (inCipher == null && outCipher == null) {
            byte[] inKey = getInKey(user);
            byte[] outKey = getOutKey(user);
            inCipher = new RC4Engine();
            outCipher = new RC4Engine();
            inCipher.init(true, new KeyParameter(inKey));
            outCipher.init(false, new KeyParameter(outKey));
            session.setAttribute("inCipher", inCipher);
            session.setAttribute("outCipher", outCipher);
        }
        String clientHex = request.getParameter("message");
        byte[] clientCiphertext = HexCodec.hexToBytes(clientHex);
        byte[] clientDecrypted = new byte[clientCiphertext.length];
        inCipher.processBytes(clientCiphertext, 0, clientCiphertext.length, clientDecrypted, 0);
        System.out.println("message = " + new String(clientDecrypted));

        String message = "Hello, this is StealthServlet.";

        byte[] plaintext = message.getBytes();
        byte[] ciphertext = new byte[plaintext.length];
        outCipher.processBytes(plaintext, 0, plaintext.length, ciphertext, 0);
        char[] hexCiphertext = HexCodec.bytesToHex(ciphertext);

        response.setContentType("text/plain");
        response.setContentLength(hexCiphertext.length);
        PrintWriter out = response.getWriter();
        out.println(hexCiphertext);
    }

    private byte[] getInKey(String user) {
        return "Outgoing MIDlet key".getBytes();
    }

    private byte[] getOutKey(String user) {
        return "Incoming MIDlet key".getBytes();
    }
}

class HexCodec {
    private static final char[] kDigits = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd',
            'e', 'f' };

    public static char[] bytesToHex(byte[] raw) {
        int length = raw.length;
        char[] hex = new char[length * 2];
        for (int i = 0; i < length; i++) {
            int value = (raw[i] + 256) % 256;
            int highIndex = value >> 4;
            int lowIndex = value & 0x0f;
            hex[i * 2 + 0] = kDigits[highIndex];
            hex[i * 2 + 1] = kDigits[lowIndex];
        }
        return hex;
    }

    public static byte[] hexToBytes(char[] hex) {
        int length = hex.length / 2;
        byte[] raw = new byte[length];
        for (int i = 0; i < length; i++) {
            int high = Character.digit(hex[i * 2], 16);
            int low = Character.digit(hex[i * 2 + 1], 16);
            int value = (high << 4) | low;
            if (value > 127)
                value -= 256;
            raw[i] = (byte) value;
        }
        return raw;
    }

    public static byte[] hexToBytes(String hex) {
        return hexToBytes(hex.toCharArray());
    }
}