[](https://github.com/mattrglobal)
# Node 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](https://github.com/mattrglobal/bbs-signatures) are a digital signature algorithm originally born from
the work on [Short group signatures](https://crypto.stanford.edu/~xb/crypto04a/groupsigs.pdf) by Boneh, Boyen, and
Shachum which was later improved on in
[Constant-Size Dynamic k-TAA](http://web.cs.iastate.edu/~wzhang/teach-552/ReadingList/552-14.pdf) as BBS+ and touched on
again in section 4.3 in
[Anonymous Attestation Using the Strong Diffie Hellman Assumption Revisited ](https://www.researchgate.net/publication/306347781_Anonymous_Attestation_Using_the_Strong_Diffie_Hellman_Assumption_Revisited).
[BBS+ Signatures](https://github.com/mattrglobal/bbs-signatures) require a
[pairing-friendly curve](https://tools.ietf.org/html/draft-irtf-cfrg-pairing-friendly-curves-03), this library includes
support for [BLS12-381](https://tools.ietf.org/html/draft-irtf-cfrg-pairing-friendly-curves-03#section-2.4).
[BBS+ Signatures](https://github.com/mattrglobal/bbs-signatures) allow for multi-message signing whilst producing a
single output signature. With a BBS signature, a [proof of knowledge](https://en.wikipedia.org/wiki/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](https://yarnpkg.com/)
```
yarn add @mattrglobal/node-bbs-signatures
```
## Usage
See the [sample](./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 | 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](https://yarnpkg.com/)
- [Rust](https://www.rust-lang.org/)
For more details see our [contribution guidelines](./docs/CONTRIBUTING.md)
#### 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](https://crates.io/crates/bbs) rust crate for the implementation of BBS+ signatures and
BLS12-381 which is then wrapped and exposed in javascript/typescript using
[neon-bindings](https://github.com/neon-bindings/neon).
## Security Policy
Please see our [security policy](./SECURITY.md) for additional details about responsible disclosure of security related
issues.
---
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