emp-wasm

Wasm build of authenticated garbling from emp-toolkit/emp-ag2pc.

(If you're not familiar with garbled circuits, you might find this video helpful.)

Usage

Take a look at mpc-framework for a nicer API which utilizes emp-wasm as a dependency. In particular, it allows you to write your circuits in a TypeScript-like language called summon.

Read on if you're more interested in what's going on under the hood and are prepared to use/write circuits like these directly.

npm install emp-wasm

import { secure2PC, BufferedIO, IO } from 'emp-wasm';

import circuit from './circuit.ts';

async function main() {
  // emp-wasm has no opinion about how you do your IO, websockets are just used
  // for this example
  const io = await makeWebSocketIO('wss://somehow-connect-to-bob');

  const output = await secure2PC(
    'alice', // use 'bob' in the other client
    circuit, // a string defining the circuit, see circuits/*.txt for examples
    Uint8Array.from([/* 0s and 1s defining your input bits */]),
    io,
  );

  // the output bits from the circuit as a Uint8Array
  console.log(output);
}

async function makeWebSocketIO(url: string) {
  const sock = new WebSocket(url);
  sock.binaryType = 'arraybuffer';

  await new Promise((resolve, reject) => {
    sock.onopen = resolve;
    sock.onerror = reject;
  });

  // You don't have to use BufferedIO, but it's a bit easier to use, otherwise
  // you need to implement io.recv(len) returning a promise to exactly len
  // bytes
  const io = new BufferedIO(
    data => sock.send(data),
    () => sock.close(),
  );

  sock.onmessage = (event: MessageEvent) => {
    if (!(event.data instanceof ArrayBuffer)) {
      console.error('Unrecognized event.data');
      return;
    }

    // Pass Uint8Arrays to io.accept
    io.accept(new Uint8Array(event.data));
  };

  sock.onerror = (e) => {
    io.emit('error', new Error(`WebSocket error: ${e}`));
  };

  sock.onclose = () => io.close();

  return io;
}

main().catch(console.error);

For a concrete example, see wsDemo in demo.ts (usage instructions further down in readme).

Demo

npm install
npm run build
npm run demo

Requirements:

• nodejs
• emscripten

internalDemo

If you don't want to juggle multiple pages, you can do await internalDemo(3, 5) in the console, which will run two instances in the same page communicating internally.

consoleDemo

Open the url in the console in two tabs and run consoleDemo('alice', 3) in one and consoleDemo('bob', 5) in the other. This will begin a back-and-forth where each page prints write(...) to the console, which you can paste into the other console to send that data to the other instance (note: sometimes there are multiple writes, make sure to copy them over in order). After about 15 rounds you'll get an alert showing 8 (== 3 + 5).

wsDemo

Open the url in the console in two tabs and run await wsDemo('alice', 3) in one and await wsDemo('bob', 5) in the other. This uses a websocket relay included in npm run demo and defined in scripts/relayServer.ts.

rtcDemo

Open the url in the console in two tabs and run await rtcDemo('pair-id', 'alice', 3) in one and await rtcDemo('pair-id', 'bob', 5) in the other. This one uses WebRTC (via peerjs) and should work across networks, locating each other via pair-id.

Regular C++ Compile

This library started out as a stripped down version of the original C++ project. You can compile this for your local system and test it like this:

./scripts/build_local_test.sh
./scripts/local_test.sh

This will calculate sha1("")==da39a3ee5e6b4b0d3255bfef95601890afd80709. It proves to Alice that Bob knows the preimage of this hash. Each side is run in a separate process and they communicate over a local socket.

Requirements:

• clang
• mbedtls (on macos: brew install mbedtls)
  • this version of mbedtls is actually not needed for the wasm version, since we need to compile a wasm-specific version ourselves

Uncertain Changes

For most of the changes I'm reasonably confident that I preserved behavior, but there some things I'm less confident about:

• send and recv swapped for bob in Fpre::generate (see TODO comment)
• after removing threading, I also moved everything to a single io channel
• rewrite of simd code to not use simd and updated aes usage written by chatgpt o1 preview
• used chatgpt o1 preview to migrate from openssl to mbedtls

Regardless, this version of emp-toolkit needs some checking.