branca

Branca

What?

Branca allows you to generate and verify encrypted authentication tokens. It defines the external format and encryption scheme of the token. Branca is based on Fernet specification. Payload in Branca token is an arbitrary sequence of bytes. Payload can be for example a JSON object, plain text string or even binary data serialized by MessagePack or Protocol Buffers.

Install

Install the library using Yarn or npm.

$ yarn add branca
$ npm install branca

Token Format

A Branca token is a base62 encoded concatenation of a header, ciphertext and MAC. Header consists of version, timestamp and nonce. Putting them all together we get the structure below.

Version || Timestamp || Nonce || Ciphertext || MAC

Version

Version is 8 bits ie. one byte. Currently the only version is 0xBA. This is a magic byte you can use to quickly identify a given token. Version number guarantees the token format and encryption algorithm.

Timestamp

Timestamp is 32 bits ie. standard 4 byte UNIX timestamp.

Nonce

Nonce is 96 bits ie. 12 bytes. These should be cryptographically secure random bytes and never reused between tokens.

Ciphertext

Payload is encrypted and authenticated using IETF ChaCha20-Poly1305. Note that this is Authenticated Encryption with Additional Data (AEAD) where the he header part of the token is the additional data. This means the data in the header (version, timestamp and nonce) is not encrypted, it is only authenticated. In laymans terms, header can be seen but it cannot be tampered.

MAC

The authentication tag is 128 bits ie. 16 bytes. This is the Poly1305 message authentication code (MAC). It is used to make sure that the message, as well as the non-encrypted header has not been tampered with.

Usage

Token payload can be any arbitrary data such as string containing an email address.

const key = "supersecretkeyyoushouldnotcommit";
const branca = require("branca")(key);

const token = branca.encode("[e-mail]");
/* 87x2GqCUw7fho4DVETyEPrv8s79gbfRIZB3ql5nliJ42xNNA88VQm7MZZzZs07O8zMC9vke0XuMxb */

const payload = branca.decode(token);
/* [e-mail] */

Sometimes you might prefer JSON.

const key = "supersecretkeyyoushouldnotcommit";
const branca = require("branca")(key);
const json = JSON.stringify({"scope": ["read", "write", "delete"]});
const token = branca.encode(json);

/*
3Gq55EruBIu2KtWGtzjjkMV45e1froWhTDF8nNNTbnwHvOeGHNHNEuBuyrGqFtEn4faf26LAuVUzijMNaO1Fk72aZ3B5
*/

const payload = JSON.parse(branca.decode(token));
/* { scope: [ 'read', 'write', 'delete' ] } */

You can keep the token size small by using a space efficient serialization method such as MessagePack or Protocol Buffers.

const key = "supersecretkeyyoushouldnotcommit";
const branca = require("branca")(key);
const msgpack = require("msgpack5")();
const packed = msgpack.encode({"scope": ["read", "write", "delete"]});
const test = msgpack.decode(packed);
const token = branca.encode(packed);
/* 2EZpnHNCn1qwjqalGcpnZ2tlpXtIqNYNqeZuQvKzz6TY8nIh1Pukl8R7ZNIFvH28ZICIi9gkikjsHaPg */

const binary = branca.decode(token);
const payload = msgpack.decode(Buffer.from(binary));
/* { scope: [ 'read', 'write', 'delete' ] } */

Testing

You can run tests either manually with the following command.

$ node test.js

Contributing

Please see CONTRIBUTING for details.

Security

If you discover any security related issues, please email [e-mail] instead of using the issue tracker.

License

The MIT License (MIT). Please see License File for more information.

Changelog

0.1.0 - 2017-07-23

Initial realease using IETF ChaCha20-Poly1305 AEAD.