zkSync Era: System Contracts
zkSync Era is a layer 2 rollup that uses zero-knowledge proofs to scale Ethereum without compromising on security or decentralization. Since it's EVM compatible (Solidity/Vyper), 99% of Ethereum projects can redeploy without refactoring or re-auditing a single line of code. zkSync Era also uses an LLVM-based compiler that will eventually let developers write smart contracts in C++, Rust and other popular languages.
system-contracts
To keep the zero-knowledge circuits as simple as possible and enable simple extensions, we created the system contracts. These are privileged special-purpose contracts that instantiate some recurring actions on the protocol level. Some of the most commonly used contracts:
ContractDeployer This contract is used to deploy new smart contracts. Its job is to make sure that the bytecode for
each deployed contract is known. This contract also defines the derivation address. Whenever a contract is deployed, a
ContractDeployed event is emitted.
L1Messenger This contract is used to send messages from zkSync to Ethereum. For each message sent, the L1MessageSent
event is emitted.
NonceHolder This contract stores account nonces. The account nonces are stored in a single place for efficiency (the
tx nonce and the deployment nonce are stored in a single place) and also for the ease of the operator.
Bootloader For greater extensibility and to lower the overhead, some parts of the protocol (e.g. account abstraction
rules) were moved to an ephemeral contract called a bootloader.
We call it ephemeral because it is not physically deployed and cannot be called, but it has a formal address that is used on msg.sender, when it calls other contracts.
Building
This repository is used as a submodule of the zksync-era.
Compile the solidity and yul contracts: yarn build
Check the system contracts hashes: yarn calculate-hashes:check
Update the system contracts hashes: yarn calculate-hashes:fix
Update Process
System contracts handle core functionalities and play a critical role in maintaining the integrity of our protocol. To ensure the highest level of security and reliability, these system contracts undergo an audit before any release.
Here is an overview of the release process of the system contracts which is aimed to preserve agility and clarity on the order of the upgrades:
main branch
The main branch contains the latest code that is ready to be deployed into production. It reflects the most stable and
audited version of the protocol.
dev branch
The dev branch is for active development & the latest code changes. Whenever a new PR with system contract changes is
created it should be based on the dev branch.
Creating a new release
Whenever a new release is planned, a new branch named release-vX-<name> should be created off the dev branch, where
X represents the release version, and <name> is a short descriptive name for the release. The PR with the new
release should point to either the main branch or to the release branch with a lower version (in case the previous
branch has not been merged into main for some reason).
Once the audit for the release branch is complete and all the fixes from the audit are applied, we need to merge the new
changes into the dev branch. Once the release is final and merged into the main branch, the main branch should be
merged back into the dev branch to keep it up-to-date.
Updating Unaudited Code
Since scripts, READMEs, etc., are code that is not subject to audits, these are to be merged directly into the main
branch. The rest of the release branches as well as the dev branch should merge main to synchronize with these
changes.
License
The zkSync Era system-contracts are distributed under the terms of the MIT license.
See LICENSE-MIT for details.
Official Links
Disclaimer
zkSync Era has been through lots of testing and audits. Although it is live, it is still in alpha state and will go through more audits and bug bounties programs. We would love to hear our community's thoughts and suggestions about it! It is important to state that forking it now can potentially lead to missing important security updates, critical features, and performance improvements.