# Smart contracts
zkSync is on track to introduce highly efficient, secure, Turing complete, multilanguage smart contracts.
# Programming model
The zkSync smart contract programming model inherits that of Ethereum.
Solidity will be supported first, so you can use unbounded loops, recursion, vectors and maps of arbitrary length, and so on. Local variables are stored on the stack or the heap, whereas the contract storage is accessed globally. Contracts call one another via strongly typed interfaces and have access to public storage fields.
# Composability
zkSync smart contracts are able to call one another just like Ethereum smart contracts can. Each call transaction tree is atomic, regardless of the number of contract instances involved.
Any DeFi project can be migrated to zkSync, since most of the existing Solidity code can be deployed without changes.
# zkEVM
The zkEVM is a highly efficient, Turing complete, SNARK-friendly virtual machine for executing smart contracts.
State-of-the-art optimizations are applied to smart contract bytecode, while the virtual machine itself is optimized for high load, allowing it to execute transactions in the blink of an eye.
The machine is SNARK-friendly; that is, the execution trace can be proven in SNARKs. However, it does not require one circuit per program. A single circuit can be used instead, which needs to be audited only once.
The target proof system of the Sync VM is PLONK (opens new window).
# Solidity
# Porting Smart Contracts
Most DeFi and NFT projects will work with no code changes. However, in the first version, calls to SHA256 and Keccak256 will be replaced with a circuit friendly hash function automatically by the compiler. A few other cryptographic primitives are currently also unsupported, for example ecrecover and the cryptographic precompiles.
# UI Interaction
You can interact completely with smart contracts and the zkSync network via our Web3 API and Ethers SDK:
- For read requests: any web3-compliant framework in any language will work out of the box, with additional optional zkSync L2 specific functionality.
- For write requests (sending transactions): due to fundamental differences between L1 and L2, you will have to write some additional code (for example, zkSync supports paying fees in any token, so sending a transaction will involve choosing a token to pay fees).
You can reuse your current frontend with only minimal changes (sending transactions is different).
# Submitting Transactions
For interactions with smart contracts, users will sign an EIP712 message with a hash of the calldata. Since EIP712 is based on a native Ethereum signature, all wallets, even hardware wallets, will work without any extensions required.
# Deployment
We will be releasing testnet soon! Please sign up on this form (opens new window).
# Zinc
Zinc (opens new window) is an emerging framework for developing smart contracts and SNARK circuits on the zkSync platform.
Existing ZKP frameworks lack functionality specific to smart contracts. Since smart contracts deal with valuable financial assets, security and safety are crucial. That's why designers of modern smart contract languages, such as Simplicity or Libra's Move, favored safety and formal verifiability of the code over expressiveness.
Zinc is created to fill the gap between these two worlds by providing a simple, reliable smart contract language that is optimized for ZKP circuits and is easy for developers to learn.
The framework includes a simple, Turing complete, safety-focused, general-purpose language designed specifically for developing smart contracts and zero-knowledge proof circuits with a flat learning curve. The syntax and semantics closely follow that of Rust (opens new window).
The Zinc compiler uses LLVM as its middle-end and back-end, which provides a powerful set of solutions for code optimization.
We are currently fully focused on a Solidity-first approach (opens new window). We will resume work on Zinc after Solidity is released!
# Getting help
Most questions are answered in our zkEVM FAQ (opens new window) and major concepts are outlined on our Medium (opens new window).
You can ask questions and get assistance in our Discord (opens new window) developer chat room.