const fs = require("fs"); const path = require("path"); const { createConnection } = require('net'); const { createHash, createECDH } = require('crypto'); const { Transform } = require('stream'); // Application settings const port = process.argv[3] || 23; const hostname = process.argv[2] || (process.pkg ? "dom.ht-dev.de" : "localhost"); let delayMs = process.argv[4] || 100; // Command delay in milliseconds // Diffie-Hellman parameters const keyCurve = "prime256v1"; // key exchange curve, make this negotiable in the future class MemoryStream extends Transform { constructor(options = {}) { super(options); } _transform(chunk, encoding, callback) { this.push(chunk); callback(); } } const writer = new MemoryStream(); let encrypted = false; // Encryption status, do not modify directly, runtime only let privateKey; // Private key, do not modify directly, runtime only const key = createECDH(keyCurve); const delay = (ms) => new Promise(resolve => setTimeout(resolve, ms)); const send = async (command) => { await delay(delayMs); writer.write(command); // Command await delay(delayMs); writer.write("\r\n"); // Line Feed }; // Numeric Buffer values const NUL = Buffer.from([0x00]); // Null const ONE = Buffer.from([0x01]); // One // Telnet commands const IAC = Buffer.from([0xff]); // Interpret As Command const DONT = Buffer.from([0xfe]); // Don't const DO = Buffer.from([0xfd]); // Do const WONT = Buffer.from([0xfc]); // Won't const WILL = Buffer.from([0xfb]); // Will const SB = Buffer.from([0xfa]); // Subnegotiation Begin const GA = Buffer.from([0xf9]); // Go Ahead const EL = Buffer.from([0xf8]); // Erase Line const EC = Buffer.from([0xf7]); // Erase Character const AYT = Buffer.from([0xf6]); // Are You There const AO = Buffer.from([0xf5]); // Abort Output const IP = Buffer.from([0xf4]); // Interrupt Process const BRK = Buffer.from([0xf3]); // Break const DM = Buffer.from([0xf2]); // Data Mark const NOP = Buffer.from([0xf1]); // No Operation const SE = Buffer.from([0xf0]); // Subnegotiation End // Common Telnet options or features const ECHO = Buffer.from([0x01]); // Echo const SUPPRESS_GO_AHEAD = Buffer.from([0x03]); // Suppress Go Ahead const STATUS = Buffer.from([0x05]); // Status const TIMING_MARK = Buffer.from([0x06]); // Timing Mark const TERMINAL_TYPE = Buffer.from([0x18]); // Terminal Type const NAWS = Buffer.from([0x1f]); // Negotiate About Window Size const TERMINAL_SPEED = Buffer.from([0x20]); // Terminal Speed const REMOTE_FLOW_CONTROL = Buffer.from([0x21]); // Remote Flow Control const LINEMODE = Buffer.from([0x22]); // Line Mode const ENVIRONMENT_VARIABLES = Buffer.from([0x24]); // Environment Variables // custom codes for own client const CUSTOM_CLIENT_INIT = Buffer.from([0x80]); // Custom Client Initialization const KEY_EXCHANGE = Buffer.from([0x81]); // Key Exchange const ENCRYPTION = Buffer.from([0x82]); // Encryption const AUTHENTICATION = Buffer.from([0x83]); // Authentication // 0x84 reserved for future use const FILE_TRANSFER = Buffer.from([0x85]); // File Transfer const PAUSE = Buffer.from([0x86]); // Pause const RESUME = Buffer.from([0x87]); // Resume const START_CONTENT = Buffer.from([0x88]); // Start Content const END_CONTENT = Buffer.from([0x89]); // End Content // Set the path of the project folder base on whether it is run with nodejs or as an executable let project_folder; if (process.pkg) { // It is run as an executable project_folder = path.dirname(process.execPath) } else { // It is run with nodejs project_folder = __dirname } if (process.pkg) { console.debug = () => { }; // Disable debug logging when run as an executable fs.writeFileSync(path.join(project_folder, "README.md"), fs.readFileSync(path.join(__dirname, "README.md"))); // copy newest readme to folder fs.writeFileSync(path.join(project_folder, "LICENSE"), fs.readFileSync(path.join(__dirname, "LICENSE"))); // copy newest license to folder } const socket = createConnection(port, hostname); writer.pipe(socket); let hold = false; // Hold input process.stdin.setEncoding("ascii"); process.stdin.setRawMode(true); process.stdin.resume(); // format keys before sending to server process.stdin.on('data', async (key) => { if (key === '\u0004') { // Ctrl+D process.exit(); } else if (key === '\u0003') { // Ctrl+C send(IP); // Interrupt Process } else if (key === '\u0018') { // Ctrl+X process.stdout.write("\r"); console.log("Entered client command mode"); hold = true; // Hold input process.stdin.setRawMode(false); // Add any additional functionality for Ctrl+X here } // Log Unicode values of input for debugging // console.debug("Key pressed:", Array.from(key).map(b => '\\u' + b.toString(16).padStart(4, '0'))); if (key == "\r") { // Enter key socket.write("\r\n"); } else if (!hold) { socket.write(key); } else { // console.debug("Input on hold"); const command = key.replace(/\r?\n|\r/g, ''); // Remove new line characters if (["exit", "quit"].includes(command)) { hold = false; // Release input process.stdin.setRawMode(true); console.log("Exited client command mode"); process.stdout.write("> "); } else if (command == "disconnect") { send(IP); // Interrupt Process } else if (command == "help") { // Add any additional functionality for client side commands console.log("Client commands:"); console.log("disconnect - Disconnect from server"); console.log("exit - Exit client command mode"); process.stdout.write("$ "); } else { process.stdout.write("$ "); } } }); socket.on("data", (data) => { if (!encrypted) { if (data.equals(PAUSE)) { process.stdin.pause(); } else if (data.equals(RESUME)) { process.stdin.resume(); } else if (data.equals(IP)) { process.exit(); } else if (data.equals(Buffer.concat([IAC, DO, CUSTOM_CLIENT_INIT]))) { // server supports custom client features socket.write(Buffer.concat([IAC, WILL, KEY_EXCHANGE])); // Start Key Exchange } else if (data.includes(Buffer.concat([IAC, DO, KEY_EXCHANGE]))) { // generate keys const publicKey = key.generateKeys(); console.debug("Generated Key: " + publicKey.toString("hex")); } else if (data.equals(Buffer.concat([IAC, SB, KEY_EXCHANGE, ONE /* value required */, IAC, SE]))) { socket.write(Buffer.concat([IAC, SB, KEY_EXCHANGE, NUL, key.getPublicKey(), IAC, SE])); // send key to server } else if (data.includes(Buffer.concat([IAC, SB, KEY_EXCHANGE, NUL /* value provided */]))) { // server sent its key, generate secret console.debug("Key exchange received"); const offsetBegin = data.indexOf(SB) + 2; const offsetEnd = data.lastIndexOf(SE) - 1; const keyData = data.subarray(offsetBegin + 1, offsetEnd); // client public key console.log("Extracted key:", keyData.toString("hex")); privateKey = key.computeSecret(keyData); socket.write(Buffer.concat([IAC, WILL, ENCRYPTION])); // Enable Encryption } else if (data.equals(Buffer.concat([IAC, DO, ENCRYPTION]))) { // enable encryption encrypted = true; console.debug("Encryption enabled"); console.debug("Private Key: " + privateKey.toString("hex")); } else { process.stdout.write(data); } } }); socket.on("connect", async () => { console.log("Connected to server"); process.stdin.pause(); // Pause input // initialization socket.write(Buffer.concat([IAC, WILL, NAWS, SB, NAWS, Buffer.from([/* 24x80 */ 0x00, 0x18, 0x00, 0x50]), SE])); // Negotiate About Window Size await delay(delayMs); // Wait for server to process socket.write(Buffer.concat([IAC, WILL, TERMINAL_TYPE, IAC, SB, TERMINAL_TYPE, NUL, Buffer.from("xterm-256color"), IAC, SE])); // Terminal Type await delay(delayMs); socket.write(Buffer.concat([IAC, DO, ECHO])); // Echo await delay(delayMs); socket.write(Buffer.concat([IAC, WILL, CUSTOM_CLIENT_INIT])); // Custom Client Initialization await delay(delayMs); // socket.write(Buffer.from([0x0d, 0x0a])); // Line Feed if (encrypted) { // increase delay for encryption delayMs += 500; } // from here on encryption is enabled, do not use socket.write() directly anymore await delay(delayMs); // initialization complete // await send("help"); await delay(500); process.stdout.write("\rCtrl+X for client side commands\r\nCtrl+C to exit, Ctrl+D to force close\r\n> "); process.stdin.resume(); // Resume input // more commands can be added here }); socket.on("end", () => { console.log("\nDisconnected from server"); process.exit(); }); module.exports = { delay, send, project_folder };