Node BBS Signatures

!npm-version
!npm-unstable-version
!Master
!Release
!codecov

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.

Getting started

To use this package within your project simply run

``
npm install @mattrglobal/node-bbs-signatures
`

Or with Yarn

`
yarn add @mattrglobal/node-bbs-signatures
`

Usage

See the sample directory for a runnable demo.

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

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

//Generate a new key pair
const keyPair = await 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 = await blsSign({
keyPair,
messages: messages,
});

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

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

//Verify the created proof
const isProofVerified = await 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 | 5G1 + (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

$3

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 test in the project run:

`
yarn test
`

#### Benchmark

To benchmark the implementation locally run:

`
yarn benchmark
``

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
neon-bindings.

Security Policy

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

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“MATTR” is a trademark of MATTR Limited, registered in New Zealand and other countries.