From 2dfeeaa8bd3e13d9bb8a398b8fb63f7bca147335 Mon Sep 17 00:00:00 2001
From: Tau <tau@nowhere>
Date: Wed, 11 Mar 2020 17:27:50 -0400
Subject: [PATCH] idz: Factor out common TCP obfuscation

---
 src/idz/common/aes.ts    | 43 ++++++++++++++++++++++++
 src/idz/common/bigint.ts | 46 ++++++++++++++++++++++++++
 src/idz/common/index.ts  |  4 +++
 src/idz/common/setup.ts  | 70 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 163 insertions(+)
 create mode 100644 src/idz/common/aes.ts
 create mode 100644 src/idz/common/bigint.ts
 create mode 100644 src/idz/common/index.ts
 create mode 100644 src/idz/common/setup.ts

diff --git a/src/idz/common/aes.ts b/src/idz/common/aes.ts
new file mode 100644
index 0000000..ede6f59
--- /dev/null
+++ b/src/idz/common/aes.ts
@@ -0,0 +1,43 @@
+import { Decipher, Cipher, createCipheriv, createDecipheriv } from "crypto";
+
+import { ByteStream } from "../../util/stream";
+
+export const BLOCK_SIZE = 16;
+
+export default class AesEcbStream implements ByteStream {
+  private readonly _dec: Decipher;
+  private readonly _enc: Cipher;
+
+  constructor(private _stm: ByteStream, keybuf: Buffer) {
+    this._dec = createDecipheriv("aes-128-ecb", keybuf, null).setAutoPadding(
+      false
+    );
+    this._enc = createCipheriv("aes-128-ecb", keybuf, null).setAutoPadding(
+      false
+    );
+  }
+
+  close() {
+    this._stm.close();
+  }
+
+  async read(nbytes: number): Promise<Buffer> {
+    if (nbytes % BLOCK_SIZE !== 0) {
+      throw new Error("Attempted to read partial cipher block");
+    }
+
+    const ciphertext = await this._stm.read(nbytes);
+
+    return this._dec.update(ciphertext);
+  }
+
+  async write(buf: Buffer): Promise<void> {
+    if (buf.length % BLOCK_SIZE !== 0) {
+      throw new Error("Attempted to write partial cipher block");
+    }
+
+    const ciphertext = this._enc.update(buf);
+
+    await this._stm.write(ciphertext);
+  }
+}
diff --git a/src/idz/common/bigint.ts b/src/idz/common/bigint.ts
new file mode 100644
index 0000000..6fbee8d
--- /dev/null
+++ b/src/idz/common/bigint.ts
@@ -0,0 +1,46 @@
+export function readBigInt(buf: Buffer) {
+  let result = 0n;
+
+  for (let i = 0; i < buf.length; i++) {
+    const shift = 8n * BigInt(i);
+    const byte = buf.readUInt8(i);
+
+    result |= BigInt(byte) << shift;
+  }
+
+  return result;
+}
+
+export function writeBigInt(n: bigint, length: number) {
+  const result = Buffer.alloc(length);
+
+  for (let i = 0; i < length; i++) {
+    const shift = 8n * BigInt(i);
+    const byte = (n >> shift) & 0xffn;
+
+    result[i] = Number(byte);
+  }
+
+  return result;
+}
+
+// i pick the one implementation language that doesn't have this built in
+
+export function modPow(b: bigint, e: bigint, m: bigint) {
+  // https://en.wikipedia.org/wiki/Modular_exponentiation#Right-to-left_binary_method
+
+  let result = 1n;
+
+  b = b % m;
+
+  while (e > 0n) {
+    if ((e & 1n) === 1n) {
+      result = (result * b) % m;
+    }
+
+    e = e >> 1n;
+    b = (b * b) % m;
+  }
+
+  return result;
+}
diff --git a/src/idz/common/index.ts b/src/idz/common/index.ts
new file mode 100644
index 0000000..35efa22
--- /dev/null
+++ b/src/idz/common/index.ts
@@ -0,0 +1,4 @@
+import setup from "./setup";
+
+export { BLOCK_SIZE } from "./aes";
+export default setup;
diff --git a/src/idz/common/setup.ts b/src/idz/common/setup.ts
new file mode 100644
index 0000000..1bff9dd
--- /dev/null
+++ b/src/idz/common/setup.ts
@@ -0,0 +1,70 @@
+import { Socket } from "net";
+
+import AesEcbStream from "./aes";
+import { readBigInt, modPow, writeBigInt } from "./bigint";
+import IoByteStream from "../../util/stream";
+
+interface RsaKey {
+  N: bigint;
+  d: bigint;
+  e: bigint;
+  hashN: number;
+}
+
+// Proof-of-concept, so we only ever use one of the ten RSA key pairs
+const rsaKey = {
+  N: 4922323266120814292574970172377860734034664704992758249880018618131907367614177800329506877981986877921220485681998287752778495334541127048495486311792061n,
+  d: 1163847742215766215216916151663017691387519688859977157498780867776436010396072628219119707788340687440419444081289736279466637153082223960965411473296473n,
+  e: 3961365081960959178294197133768419551060435043430437330799371731939550352626564261219865471710058480523874787120718634318364066605378505537556570049131337n,
+  hashN: 2662304617,
+};
+
+// Proof-of-concept, so we only use one fixed session key
+const aesKey = Buffer.from("ffddeeccbbaa99887766554433221100", "hex");
+
+function writeServerHello(aesKey: Buffer, rsaKey: RsaKey) {
+  const M = readBigInt(aesKey);
+  const keyEnc = modPow(M, rsaKey.e, rsaKey.N);
+  const result = Buffer.alloc(0x48);
+
+  result.set(writeBigInt(keyEnc, 0x40), 0x00);
+  result.writeUInt32LE(0x01020304, 0x40); // Meaning is unknown
+  result.writeUInt32LE(rsaKey.hashN, 0x44);
+
+  return result;
+}
+
+function readClientHello(buf: Buffer) {
+  const magic = buf.readUInt32LE(0x00);
+
+  if (magic !== 0x01020304) {
+    throw new Error(
+      "Invalid magic number, cryptographic processing probably incorrect."
+    );
+  }
+
+  return {
+    pcbId: buf.slice(0x04, 0x0f).toString("ascii"),
+    protocol: buf.slice(0x10, 0x13).toString("ascii"),
+    model: buf.slice(0x18, 0x0c).toString("ascii"),
+  };
+}
+
+export default async function setup(socket: Socket) {
+  const tcpStream = new IoByteStream(socket);
+  const serverHello = writeServerHello(aesKey, rsaKey);
+
+  await tcpStream.write(serverHello);
+
+  const aesStream = new AesEcbStream(tcpStream, aesKey);
+
+  const response = await aesStream.read(0x30);
+
+  if (response.length !== 0x30) {
+    throw new Error("Truncated client hello");
+  }
+
+  const clientHello = readClientHello(response);
+
+  return { aesStream, clientHello };
+}