consensys / zslbox

ZSLBox offers some grpc endpoints to generate and verify proofs "à la ZCash": shielding, unshielding and shielded transfers.

Warning: ZSLBox is not production ready and should not be deemed secure. For instance, there is no gRPC certificate verification.

ZSLBox

ZSLBox offers some grpc endpoints to generate and verify proofs "à la ZCash": shielding, unshielding and shielded transfers. It is derived from Quorum ZSL published in Oct. 2017 by the the ZCash team & JPM, and uses libsnark as a backend.

ZSLBox is blockchain agnostic, and can easily be integrated in Ethereum clients through precompiled contracts.

See running the tests for example usage.

See simple geth fork for example integration.

The ZCash protocol specification is a must read.

Getting Started

These instructions will get you a copy of the project up and running on your local machine for development and testing purposes.

Prerequisites

Libraries: the server needs to link with libsnark / libzsl.

go build will work on any platform, but libzsl compile script is provided only for Linux (see Dockerfile). On MacOS and Windows, it doesn't link with libzsl and mocks the snark related APIs.

Running

The easiest way to build and run ZSLBox is through docker. zkSNARK computation is memory hungry, you'll need to increase Docker RAM allocation (default is 2GB)

docker pull pegasystech/zslbox:latest
docker volume create zslkeys
docker run -p9000:9000 -p9001:9001 -d --name zslbox --mount source=zslkeys,target=/keys pegasystech/zslbox:latest 

Note: the proving and verifying keys will be generated (aka trusted setup) only if not present in /keys. It takes about a minute on a standard laptop.

Building

Clone the repo

go get -u github.com/consensys/zslbox

Compile libsnark, libzsl and zslbox

docker build . -t zslbox

Create a volume that will hold the proving and verifying keys

docker volume create zslkeys

Start ZSLBox

docker run -p9000:9000 -p9001:9001 --rm --name zslbox --mount source=zslkeys,target=/keys zslbox:latest 

API Overview

Checkout zslbox.proto for a quick overview of the APIs ZSLBox offers.

Running the tests

The files client.go and client_test.go in the zsl package demonstrate how to connect to the gRPC server (ZSLBox), generate and verify proofs.

cd zsl
ZSLBOX_URL=localhost:9000 go test

note: you can ommit ZSLBOX_URL env variable if you're running ZSLBox on localhost:9000 - default value

Create and verify shielding

A shielding operation will take a Note as input. it returns the proof (zkSNARK) and the commitment derived from the Note. It also returns a send nullifier (different from the spend nullifier) that ensures the random parameter in the note Rho is unique.

Typically, a blockchain would enforce the validity of the shielding operation; it would ensure your balance on the ledger (in clear) is bigger than the value of the note you created and shielded.

// connect to ZSLBox
client, err := NewClient(zslboxURL)
defer client.Close()

// generate a new ZAddress (Pk, Sk)
address, err := client.ZSLBox.GetNewAddress(context.Background(), &Void{})

// create a Note
note := &Note{
	Pk:    address.Pk,
	Rho:   RandomBytes(HashSize),
	Value: rand.Uint64(),
}

// shielding operation
shielding, err := client.ZSLBox.CreateShielding(context.Background(), note)
// shielding.Snark, shielding.Commitment, shielding.SendNullifier

// verify the proof generated above
verifyResult, err := client.ZSLBox.VerifyShielding(context.Background(), &VerifyShieldingRequest{Shielding: shielding, Value: note.Value})

Create and verify unshielding

The unshielding and shielded transfer operations (and circuits) are more complex than the shielding one. Among other things, you'll want to prove than you know a tuple (Note, Note Commitment) such that Note Commitment is in a Merkle tree at a specific index. For testing purposes, the zsl package provides a Tree that stores commitments and provides witnesses for our operations (treeRootand treePath, aka Merkle Tree authentication path).

// commitment tree
tree := NewTree(TreeDepth)
cm, err := client.ZSLBox.GetCommitment(context.Background(), note)
tree.AddCommitment(cm)

// get witnesses for our circuit
treeIndex, treePath, err := tree.GetWitnesses(cm)

// a known Note
shieldedInput := &ShieldedInput{
	Sk:        address.Sk,
	Rho:       note.Rho,
	Value:     note.Value,
	TreeIndex: uint64(treeIndex),
	TreePath:  treePath,
}

// unshielding
unshielding, err := client.ZSLBox.CreateUnshielding(context.Background(), shieldedInput)

// verify unshielding
treeRoot := tree.Root()
verifyRequest := &VerifyUnshieldingRequest{
	Snark:          unshielding.Snark,
	SpendNullifier: unshielding.SpendNullifier,
	Value:          note.Value,
	TreeRoot:       treeRoot[:],
}
verifyResult, err := client.ZSLBox.VerifyUnshielding(context.Background(), verifyRequest)

Known issues

• ZSLBox container leaks memory. More specifically, the "CreateShieldedTransfer" has a 20% failure rate on a large number of tests (Shielding and Unshielding are close to 0% failure). Not a graceful crash.

Developers

gRPC

You'll need to install protobuf, grpc and protoc-gen-go (or other plugin if you want to generate a client for another language; ex protoc-gen-grpc-java). Instructions here.

Regenerate zslbox.pb.go from zslbox.proto, at the root of the repo:

go generate

Formatting

We use go fmt. If you don't have a plugin to run it automatically in your Go environment, consider using our pre-commit hook

ln -s $(pwd)/pre-commit .git/hooks/

Dependencies (/vendor)

ZSLBox uses dep for dependency management.

Contributing

Please read CONTRIBUTING.md for details on our code of conduct, and the process for submitting pull requests to us. Get in touch: [email protected]

Versioning

We use SemVer for versioning. For the versions available, see the tags on this repository.

License

This project is licensed under the Apache 2 License - see the LICENSE file for details

Acknowledgments

• The ZCash team - Amazing work on Zero Security Layer and ZCash protocol specification - Original Copyright 2017 Zerocoin Electric Coin Company LLC