The vision of Ethereum has always been to enable inclusive, decentralized finance for everyone. However, with nearly all transactions processed on Layer1 (L1), the network often suffers from congestion and high gas fees—barriers that prevent many users from participating. To address this, the community has turned to Layer2 (L2) scaling solutions, among which zkSync stands out as a leading implementation of zkRollup technology.
Backed by Ethereum co-founder Vitalik Buterin’s endorsement of ZK Rollups as the long-term winner in scaling, zkSync offers a secure, scalable, and low-cost way to transact crypto assets. This guide dives into the core principles, architecture, and operational mechanics of zkSync—helping you understand how it works and why it matters.
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What Is zkSync?
zkSync is a Layer2 scaling protocol built on the ZK Rollup framework. It leverages zero-knowledge proofs (ZK-SNARKs) and on-chain data availability to ensure asset security while drastically reducing transaction costs and confirmation times.
As stated in its slogan:
zkSync: secure, scalable crypto payments
Currently focused on payment use cases, zkSync delivers near-instant transaction finality on L2 and final settlement on Ethereum L1 within minutes—offering a seamless user experience without compromising decentralization or security.
Core Features
- Supports ETH and ERC20 token transfers
- Millisecond confirmations on L2; finality on L1 in ~10 minutes
- Full Ethereum-level security—no reliance on trusted third parties
- Zero-cost account creation
- Extremely low fees (as low as $0.001 per transaction)
- Accepts any valid Ethereum address (including smart contracts)
- Pay gas fees using any supported token (e.g., DAI)
- Fast withdrawals (within 15 minutes, compared to 1–2 weeks for Optimistic Rollups)
- Supports multisig and upcoming smart contract functionality
Key Advantages
- Funds are always safe: Validators cannot alter state or steal funds.
- Censorship resistance: Even if validators go offline, users can independently withdraw funds thanks to data availability.
- No need for constant monitoring: Unlike fraud-proof systems, zkSync doesn’t require users to watch the network for malicious activity.
How zkSync Works: The Technical Overview
At its core, zkSync operates by bundling thousands of off-chain transactions and submitting a compressed cryptographic proof to Ethereum. This process ensures scalability while maintaining trustless security.
Step-by-Step Workflow
- User submits transaction: A user signs a transaction and sends it to a validator (also called a "prover").
- Transaction batching: The validator aggregates many transactions into a single batch.
- Proof generation: Using the Plonk proving system, the validator generates a zero-knowledge proof (SNARK) that verifies the correctness of the new state transition.
- On-chain submission: The proof, along with minimal transaction data (via cheap calldata), is submitted to the L1 smart contract.
- Verification & finality: The smart contract verifies the proof. Once confirmed, all transactions in the batch achieve final settlement.
This model ensures that even if the validator acts maliciously, invalid state changes will be rejected by the L1 contract—making zkSync fundamentally secure.
zkSync Architecture: On-Chain and Off-Chain Components
zkSync’s architecture is divided into two main layers: on-chain (L1) and off-chain (L2) components.
On-Chain (L1)
The L1 component consists of a smart contract deployed on Ethereum. It handles:
- Deposits
- Withdrawals
- Transaction verification via SNARK proofs
- State root updates
All critical operations are validated on Ethereum, ensuring maximum security.
Off-Chain (L2)
The L2 system manages user interactions and state processing through several key modules:
- Watcher: Monitors L1 for deposit events and triggers L2 balance updates.
- Mempool: Holds pending transactions before they’re processed.
- Block Proposer: Packages transactions into blocks.
- State Keeper: Maintains the current state of accounts.
- Block Commiter: Gathers data needed for proof generation.
- Sender: Submits transaction data and proofs to L1.
- Plonk Proving System: Generates zero-knowledge proofs for state transitions.
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User Journey: From Deposit to Withdrawal
Let’s walk through the typical user flow in zkSync.
1. Deposit
To begin using zkSync, users must first deposit funds from Ethereum L1.
On L1:
- The user calls the zkSync smart contract to deposit ETH or an ERC20 token.
- They can specify the target zkSync address.
- Only whitelisted tokens are accepted; others may revert.
On L2:
- After ~10 Ethereum block confirmations, Watcher detects the deposit.
- Funds are credited to the user’s zkSync account.
- If the account doesn’t exist, it’s automatically created—no setup cost.
2. Account & Signer Management
zkSync uses a unique account model where each Ethereum address maps to a zkSync-specific identity.
Key Concepts:
- Each account has an ID linked to an Ethereum address, public key, nonce, and balance.
- A zkSync Signer is derived when initiating transfers or withdrawals.
- The signer is generated via
personalSign, used only for L2 transaction authorization. - The first time a user sends funds, they must set their signing key using the SDK (
setSigningKey). - After setup, users don’t need to manage signers manually.
Note: While receiving funds uses standard Ethereum addresses, all outgoing transactions are signed with the zkSync Signer under the hood.
3. Transfer
Transfers in zkSync mirror Ethereum’s UX but with major improvements.
Key Details:
Recipient Address: Any valid Ethereum address can receive funds.
- Sending to a non-existent account incurs higher fees due to account creation.
- Token Support: In theory supports all ERC20s, but currently limited to whitelisted tokens.
- Gas Flexibility: Users can pay fees in any supported token (e.g., USDT, DAI).
Fee Breakdown:
- On-chain (~1.9k gas): SNARK verification + state update
- Off-chain (~$0.001 per tx): Proof generation and storage
Transaction States:
- Committed: Achieved in seconds—transaction is accepted on L2 and allows follow-up actions.
- Verified: Finality achieved in ~10 minutes after L1 contract confirms the proof.
4. Withdrawal Options
zkSync offers three withdrawal methods depending on user needs:
A. Standard Withdraw
- Type: L2-initiated
- Time: ~10 minutes to ~4 hours (based on speed preference)
- Requirement: User must control the private key of the recipient address
B. ForcedExit
- Type: L2-initiated
- Time: Variable
- Use Case: For withdrawing funds sent to smart contracts or exchanges where private keys aren’t accessible
- Process: Submit a manual request form for manual processing
C. FullExit
- Type: L1-initiated
- Time: Up to 1 week
- Use Case: Emergency exit during validator failure or network unavailability
- Mechanism: Users submit an exit proof directly to the L1 contract to reclaim funds
Frequently Asked Questions (FAQ)
Q: Is zkSync safe compared to other Layer2 solutions?
A: Yes. Unlike Optimistic Rollups that rely on challenge periods and fraud proofs, zkSync uses cryptographic validity proofs. This means transactions are verified instantly and securely—no waiting period or assumption of honest actors.
Q: Can I use any wallet with zkSync?
A: Most Ethereum-compatible wallets work for deposits and receiving funds. However, for sending transactions, you’ll need a wallet that supports zkSync Signer derivation—such as imToken or official zkSync wallets.
Q: Why are some tokens not supported?
A: zkSync maintains a token whitelist for security and compatibility reasons. Unlisted tokens may cause issues during transfers or deposits.
Q: Do I need to keep my zkSync signer private key?
A: No—the signer key is derived deterministically from your Ethereum wallet signature. As long as you retain access to your original wallet, you can regenerate it anytime.
Q: How does zkSync handle censorship or downtime?
A: Thanks to full data availability on Ethereum, users can always withdraw funds independently—even if validators stop producing blocks.
Q: Will zkSync support smart contracts?
A: Yes. While current focus is on payments, full EVM-compatible smart contract support (zkEVM) is actively being developed and will unlock DeFi, NFTs, and more.
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With its blend of security, speed, and low cost, zkSync represents a major leap forward in blockchain scalability. Whether you're a developer building on Layer2 or a user tired of high gas fees, zkSync offers a compelling solution rooted in cryptographic truth.
As ZK technology evolves and adoption grows, protocols like zkSync are poised to power the next generation of decentralized applications—bringing Ethereum closer to its original promise of open, global finance.