bbs-signatures

This repository is the home to a performant multi-message digital signature algorithm implementation which supports deriving zero knowledge proofs that enable selective disclosure from the originally signed message set.

BBS+ Signatures are a digital signature algorithm originally born from the work on Short group signatures by Boneh, Boyen, and Shachum which was later improved on in Constant-Size Dynamic k-TAA as BBS+ and touched on again in section 4.3 in Anonymous Attestation Using the Strong Diffie Hellman Assumption Revisited .

BBS+ signatures require a pairing-friendly curve, this library includes support for BLS12-381.

BBS+ Signatures allow for multi-message signing whilst producing a single output signature. With a BBS signature, a proof of knowledge based proof can be produced where only some of the originally signed messages are revealed at the discretion of the prover.

For more details on the signature algorithm please refer to here.

Getting started

To use this package within your project simply run

npm install @mattrglobal/bbs-signatures

Or with Yarn

yarn add @mattrglobal/bbs-signatures

Using via CDN in browser

To use this library in browser via the unpkg CDN, include the following script element in your HTML

<script type="text/javascript" src="https://unpkg.com/@mattrglobal/bbs-signatures/dist/bbs-signatures.min.js"></script></body>

Environment Support

This library includes a couple of features to ensure the most performant implementation of BBS is running in a execution environment. The order of selection is the following.

1. If in a node js based environment and the optional dependency of @mattrglobal/node-bbs-signatures is installed use this.
2. If in an environment that supports Web Assembly use this.
3. Else use a version compiled to asm.js.

Note Please refer to running the benchmarks below where you can compare these different implementations, the differences are very notable.

Note To force the usage of a particular environment set the BBS_SIGNATURES_MODE environment variable to one of the following values

• NODE_JS_MODULE - Use native node module, ensure @mattrglobal/node-bbs-signatures is installed
• WASM - Use the wasm module
• ASM_JS - Use the asm.js module

React Native

Currently Web Assembly support in javascript environments like react native is not official.

To enable support, this library features an asm.js version of the library that is complied from the Web Assembly module using wasm2js from the binaryen project. When this library is being used in an environment where Web Assembly is not detected this asm.js fall back is used.

Usage

See the sample directory for a runnable demo's.

The following is a short sample on how to use the API

import {
  generateBls12381G2KeyPair,
  blsSign,
  blsVerify,
  blsCreateProof,
  blsVerifyProof,
} from "@mattrglobal/bbs-signatures";

//Generate a new key pair
const keyPair = generateBls12381G2KeyPair();

//Set of messages we wish to sign
const messages = [
  Uint8Array.from(Buffer.from("message1", "utf-8")),
  Uint8Array.from(Buffer.from("message2", "utf-8")),
];

//Create the signature
const signature = blsSign({
  keyPair,
  messages: messages,
});

//Verify the signature
const isVerified = blsVerify({
  publicKey: keyPair.publicKey,
  messages: messages,
  signature,
});

//Derive a proof from the signature revealing the first message
const proof = blsCreateProof({
  signature,
  publicKey: keyPair.publicKey,
  messages,
  nonce: Uint8Array.from(Buffer.from("nonce", "utf8")),
  revealed: [0],
});

//Verify the created proof
const isProofVerified = blsVerifyProof({
  proof,
  publicKey: keyPair.publicKey,
  messages: messages.slice(0, 1),
  nonce: Uint8Array.from(Buffer.from("nonce", "utf8")),
});

Element Size

Within a digital signature there are several elements for which it is useful to know the size, the following table outlines the general equation for calculating element sizes in relation to BBS+ signatures as it is dependent on the pairing friendly curve used.

Element	Size Equation
Private Key	F
Public Key	G2
Signature	G1 + 2*F
Proof	5*G1 + (4 + no_of_hidden_messages)*F

• F A field element
• G1 A point in the field of G1
• G2 A point in the field of G2
• no_of_hidden_messages The number of the hidden messages

This library includes specific support for BLS12-381 keys with BBS+ signatures and hence gives rise to the following concrete sizes

Element	Size with BLS12-381
Private Key	32 Bytes
Public Key	96 Bytes
Signature	112 Bytes
Proof	368 + (no_of_hidden_messages)*32 Bytes

Getting started as a contributor

The following describes how to get started as a contributor to this project

Prerequisites

The following is a list of dependencies you must install to build and contribute to this project

• Yarn
• Rust

For more details see our contribution guidelines

Install

To install the package dependencies run:

yarn install --frozen-lockfile

Build

To build the project run:

yarn build

Test

To run the all test in the project run:

yarn test

To run just the tests for a node environment using the native node module of @mattrglobal-node-bbs-signatures run:

yarn test:node

To run just the tests for a node environment using the wasm module run:

yarn test:wasm

To run just the tests for a node environment using the asm.js module run:

yarn test:asm

To run just the tests for a browser environment run:

yarn test:browser

Benchmark

To benchmark the implementation locally in a node environment using the native node module of @mattrglobal-node-bbs-signatures run:

yarn benchmark:node

To benchmark the implementation locally in a node environment using the wasm module run:

yarn benchmark:wasm

To benchmark the implementation locally in a node environment using the asm.js module run:

yarn benchmark:asm

Dependencies

This library uses the bbs rust crate for the implementation of BBS+ signatures and BLS12-381 which is then wrapped and exposed in javascript/typescript using Web Assembly.

Security Policy

Please see our security policy for additional details about responsible disclosure of security related issues.

Relevant References

For those interested in more details, you might find the following resources helpful

• Details on the algorithm
• BLS12-381 For The Rest Of Us
• Pairing-based cryptography
• Exploring Elliptic Curve Pairings
• Anonymous Attestation Using the Strong Diffie Hellman Assumption Revisited
• Pairing Friendly Curves
• BLS Signatures

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