x3dh

TypeScript implementation of X3DH, as described in Going Bark: A Furry's Guide to End-to-End Encryption.

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The install size is kind of large because this package includes a pre-bundled sodium.

fork

This is a fork of soatok/rawr-x3dh.

Contents

• What's This?
• Installation
• Usage
• Should I Use This?

What's This?

This library implements the Extended Triple Diffie-Hellman key exchange, with a few minor tweaks:

1. Identity keys are Ed25519 public keys, not X25519 public keys. See this for an explanation.
2. Encryption/decryption and KDF implementations are pluggable (assuming you implement the interface I provide), so you aren't married to HKDF or a particular cipher. (Although I recommend hard-coding it to your application!)

Installation

npm i -S @substrate-system/x3dh

If you're working server-side, you'll also want to install sodium-native, so that sodium-plus will run faster.

If you're working in a browser or browser extension, don't install sodium-native.

Usage

First, you'll want to import the X3DH class from our module.

import { X3DH } from '@substrate-system/x3dh'

const x3dh = new X3DH()

Note: You can pass some classes to the constructor to replace my algorithm implementations for your own.

import { X3DH } from '@substrate-system/x3dh'

const x3dh = new X3DH(
    sessionKeyManager,  /* SessionKeyManagerInterface */
    identityKeyManager,  /* IdentityKeyManagerInterface */
    symmetricEncryptionHandler,  /* SymmetricEncryptionInterface */
    keyDerivationFunction  /* KeyDerivationFunction */
)

Once your X3DH object's instantiated, you will be able to initialize handshakes either as a sender or as a recipient. Then you will be able to encrypt additional messages on either side, and the encryption key shall ratchet forward.

const firstEncrypted = await x3dh.initSend(
    'recipient@server2',
    serverApiCallFunc,
    firstMessage
); 

The serverApiCallFunc parameter should be a function that sends a request to the server to obtain the identity key, signed pre-key, and optional one-time key for the handshake.

See the definition of the InitClientFunction type in lib/index.ts.

Once this has completed, you can call encryptNext() multiple times to append messages to send.

const nextEncrypted = await x3dh.encryptNext(
    'recipient@server2',
    'This is a follow-up message UwU'
);

On the other side, your communication partner will use the following feature.

const [sender, firstMessage] = await x3dh.initRecv(senderInfo);
const nextMessage = await x3dh.decryptNext(sender, nextEncrypted);

Note: initRecv() will always return the sender identity (a string) and the message (a Buffer that can be converted to a string). The sender identity should be usable for decryptNext() calls.

However, that doesn't mean it's trustworthy! This library only implements the X3DH pattern. It doesn't implement the Gossamer integration.

Should I Use This?

Don't use it in production until version 1.0.0 has been tagged. The API can break at any moment until that happens (especially if I decide I hate the default key management classes I wrote).

However, feel free to test and play with it.