ZK Sync: scaling and privacy engine for Ethereum

Check out ZK Sync live demo.

ZK Sync is a scaling and privacy engine for Ethereum. Its current functionality scope includes low gas transfers of ETH and ERC20 tokens in the Ethereum network. This document is a description of the JS library that can be used to interact with ZK Sync.

ZK Sync is built on ZK Rollup architecture. ZK Rollup is an L2 scaling solution in which all funds are held by a smart contract on the mainchain, while computation and storage are performed off-chain. For every Rollup block, a state transition zero-knowledge proof (SNARK) is generated and verified by the mainchain contract. This SNARK includes the proof of the validity of every single transaction in the Rollup block. Additionally, the public data update for every block is published over the mainchain network in the cheap calldata.

This architecture provides the following guarantees:

• The Rollup validator(s) can never corrupt the state or steal funds (unlike Sidechains).
• Users can always retrieve the funds from the Rollup even if validator(s) stop cooperating because the data is available (unlike Plasma).
• Thanks to validity proofs, neither users nor a single other trusted party needs to be online to monitor Rollup blocks in order to prevent fraud.

In other words, ZK Rollup strictly inherits the security guarantees of the underlying L1.

To learn how to use ZK Sync, please refer to the ZK Sync SDK documentation.

Prerequisites

Prepare dev environment prerequisites: see docs/setup-dev.md

Setup local dev environment

Setup:

zksync init

During first init you have to download around 8 GB of setup files, this should be done once. If you have problem on this step of init see help of the zksync plonk-setup.

To completely reset the dev environment:

• Stop services:

  zksync dev-down

• Repeat the setup procedure above

(Re)deploy db and contraсts:

zksync redeploy

Environment configurations

Env config files are held in etc/env/

List configurations:

zksync env

Switch between configurations:

zksync env <ENV_NAME>

Build and run server + prover locally for development:

Run server:

zksync server

Server is configured using env files in ./etc/env directory. After first init you should have ./etc/env/dev.env file copied from ./etc/env/dev.env.example.

Server can produce block of different sizes, all available sizes are in the SUPPORTED_BLOCK_CHUNKS_SIZES env variable. You can select wich of these block sizes are produced by you server using BLOCK_CHUNK_SIZES env variable.

Note: for proof generation for large blocks you need a lot of resources and on average user machine you should be able to proof only the smallest of the available block sizes.

After that you may need to invalidate cargo cache by touching the files of models:

touch core/models/**/*.rs

This is required, because models take the environment variable value at the compile time, and we have to recompile this module to set correct values.

If you use additional caching systems (like sccache), you may have to remove their cache as well.

Run prover:

zksync prover

Run client

zksync client

Client UI will be available at http://localhost:8080. Make sure you have environment variables set right, you can check it by running: zksync env. You should see * dev in output.

Build and push images to dockerhub:

zksync dockerhub-push

Development

Database migrations

• cd core/storage

• Add diesel migration
• Rename core/storage/schema.rs.generated to schema.rs
• Run tests:

  zksync db-tests

Testing

• Running all the rust tests:

  f cargo test

• Running the database tests:

  zksync db-tests

• Running the integration test:

  zksync server # Has to be run in the 1st terminal
  zksync prover # Has to be run in the 2nd terminal
  zksync integration-simple # Has to be run in the 3rd terminal

• Running the full integration tests (similar to integration-simple, but performs different full exits)

  zksync server # Has to be run in the 1st terminal
  zksync prover # Has to be run in the 2nd terminal
  zksync integration-full-exit # Has to be run in the 3rd terminal

• Running the circuit tests:

  zksync circuit-tests

• Running the prover tests:

  zksync prover-tests

• Running the benchmarks:

  f cargo bench

• Running the loadtest:

  zksync server # Has to be run in the 1st terminal
  zksync prover # Has to be run in the 2nd terminal
  zksync loadtest # Has to be run in the 3rd terminal

Developing circuit

• To generate proofs you need universal setup files that you downloaded during first init.
• To verify generated proofs you need verification keys for generated for specific circuit and Verifier.sol contract to check proofs on the Ethereum network.

Steps to do after updating circuit:

1. Update circuit version by updating KEY_DIR in your env file (don't forget to place it to dev.env.example) (last parts of this variable usually means last commit where you updated circuit).
2. Regenerate verification keys and Verifier contract using zksync verify-keys gen command.
3. Pack generated verification keys using zksync verify-keys pack command and commit resulting file to repo.

Contracts

Re-build contracts:

zksync build-contracts

Publish source code on etherscan

zksync publish-source

License

ZK Sync is distributed under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-APACHE, LICENSE-MIT for details.