zkLink: An Aggregated Rollup Infrastructure
Based on Zero-Knowledge Technology

Abstract
The proliferation of new blockchain networks has resulted in fragmented liquidity andincreased complexity in deploying dApps across multiple blockchains. The absence of aplatform that facilitates secure trading of cross-chain assets with interoperability would bringsignificant challenges for the mass adoption of DApps. Developers are confronted with the
intricacies of deploying dApps across different chains due to variations in programming
languages and tools.
In response to these obstacles, zkLink is actively developing an aggregated rollup infrastructure,
secured by zero-knowledge proof and multi-chain state synchronization, to interconnect various
Layer 1 (L1) and Layer 2 (L2) ecosystems. By aggregating native crypto assets from separate
blockchain networks onto a unified platform, zkLink simplifies the complexities associatedwith deploying dApps across multiple chains. Additionally, it aims to unify fragmented
liquidity across ecosystems and significantly reduce transaction costs.

1 Introduction
With the rapid advancement of the blockchain space, a multi-chain, multi-layer landscape has
emerged with the presence of layer 1 blockchains like Ethereum, Solana, Avalanche, andEthereum layer 2 rollups such as Arbitrum, zkSync, Starknet. Users navigate between different
L1 chains and L2 rollups to meet their specific needs, utilizing a diverse array of crypto tokens.
While the proliferation of new chains and rollups presents significant value for crypto users
worldwide, it also poses unforeseen challenges of ecosystem fragmentation. For users, thisleads to increased costs and security risks for cross-chain transactions, and for developers, acomplex multi-chain dApp development environment.

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zkLink addresses the above issues by building an aggregated rollup infrastructure to achievecross-chain liquidity aggregation and simplify multi-chain dApp deployment. Through multichain state synchronization, dApps can securely access the liquidity from any connected chains.
By leveraging zero-knowledge proof technology, it provides a high throughput, low-cost andsecure environment for the dApps of any kind.
Key features of zkLink infrastructure include:
Native Asset Aggregation: Applications using zkLink infra solution will be able to access thenative tokens across the connected L1s and L2s, allowing users to trade multi-chain assets on aunified user interface.
Low Fee and High Scalability: zkLink's modular stack provides unparalleled scalability fordApps building on top of our ecosystem. Zero-knowledge proof technology can dramaticallyreduce execution costs and provide for a blazing-fast user experience.
Minimum Security Assumption: Every transaction on zkLink infra undergoes verification via
zero-knowledge proof. Third party asset bridges are not needed for bridging assets onto zkLink
infra, thus eliminating cross-chain asset bridging risks. Multi-chain state synchronization isachieved via transmitting sync hash of on-chain transactions, which prevents malicious
operation like sending fraud deposit information.
Currently, zkLink serves two product lines:
zkLink Nova: zkLink Nova is an EVM-compatible, aggregated Layer 3 rollup network built
on top of Ethereum and its Layer 2 Rollups. DApp developers can deploy Solidity smart
contracts on Nova’s open platform and have immediate access to liquidity and native assets
from all the integrated networks, such as Ethereum, Arbitrum, zkSync, Linea, and many others.
Nova inherits Ethereum security by achieving multi-chain state synchronization via an
Ethereum smart contracts, which forwards on-chain transaction sync hashes through thecanonical rollup bridges.
zkLink X: zkLink X is an aggregated rollup infrastructure for customized high performance
applications with their own sovereignty. zkLink X serves as a middle-ware that abstracts away
the complexity of multi-chain deployment, making developers feel like building on a single
chain with multi-chain liquidity. Its modular architecture allows developers to customize thekey components, for example, DA solution and multi-chain settlement scheme, to meet diverse
demands of different use cases. It provides a trading-specific-zkVM that empowers highthroughput, low-cost App Rollup solution for high performance financial applications such asorder book DEX.

2 zkLink Protocol Design
2.1 Protocol Overview
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Figure 1: zkLink Protocol Design
zkLink Protocol is an aggregated ZK-Rollup Infrastructure with a modular architecture,
allowing for various components or modules to be easily interchanged, upgraded, or added asneeded. This modular approach provides flexibility and scalability by combining multiple
specialized blockchains and technologies.
zkLink Protocol is composed of four layers: the settlement layer, the execution layer, thesequencing layer, and the DA layer. These four layers are decoupled for customized rollup
deployment. The following sections will introduce the protocol from the perspective of the four
layers. It is important to note that the core value proposition and most innovations of the zkLink
protocol are related to the settlement layer solutions and the execution layer solutions.

2.2 Settlement Layer
A classic ZK-Rollup network typically selects a single chain, i.e, Ethereum as the settlement
layer to verify the proofs and settle the transactions. The settlement layer maintains the security
and integrity of off-chain transactions.
In comparison to a classic ZK-Rollup architecture, zkLink proposes an aggregated ZK-Rollup,
a new type of ZK-Rollup architecture which integrates with multiple blockchains. In order tosecurely aggregate native token assets across L1s and L2s onto one single platform, users' assets
are locked inside the rollup bridge contracts deployed on the connected chains. Additionally,
the aggregated ZK-Rollup securely synchronizes multi-chain state via sync hash of on-chaintransactions using canonical rollup bridges, preventing malicious operations like fraud deposit.
zkLink offers two types of proprietary settlement solutions, zkLink Nexus and zkLink Origin,each designed to meet different network integration requirements.

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Solutions

zkLink Nexus

zkLink Origin

Supported Networks

Security Assumption

Ethereum and its L2sEthereum Equivalent

Ethereum, Alt-L1s and L2s

The Sequencer and the Light Oracle
Network cannot collude formalicious activities

Table 1: zkLink Nexus vs. Origin Settlement Solutions

2.2.1 Working Principle of An Aggregated ZK-Rollup

Figure 2: zkLink Settlement Architecture
In the architecture of an aggregated ZK-Rollup, on-chain transactions such as deposits will be
relayed to the rollup network in real-time to deliver the best user experience. However, the hard
finality of every transaction is achieved by multi-chain settlement, a new settlement paradigm
which depends on the result of ZKP verification and multi-chain state synchronization.
In order to optimize the verification cost, only one chain among the connected chains will be
designated as the primary chain, which is responsible for ZKP verification. While the otherchains will act as secondary chains that do not need to execute ZKP verification, throughmulti-chain state synchronization, it is equivalent to completing the verification on all chains.
The working principle of a classic ZK-Rollup typically contains three stages: the Commit stage,
Prove stage, and Execute stage. zkLink’s aggregated ZK-Rollup architecture introduces anadditional Synchronization stage following the Prove stage. The Synchronization stage
validates the consistency of all on-chain transactions in a transaction batch verified by ZKP.
The 4 stages are briefly described as below:
41. Commit: The sequencer submits the zk-proof and transaction batch to the verifier contract
on the primary chain.
2. Prove: The zkLink contract on the primary chain verifies the validity of the zk-proof.
3. Synchronization: The transaction sync hashes of secondary chains are forwarded to theprimary chain via secure message channels. The primary chain verifies if sync hashes are
consistent with the on-chain transactions previously relayed by the sequencer. Upon theverification of both ZKP and on-chain transaction consistency, the transaction batch can befinalized and the batch root will be sent to secondary chains for execution.
4. Settlement Execute: After receiving the batch root of the transactions including the Merkle
Proof for fund withdrawal, fund withdrawals will be approved and executed.

2.2.2 Nexus: Settlement on Ethereum and its L2sThe zkLink Nexus settlement solution only connects to Ethereum and its L2s. Nexus introduces
a new paradigm of multi-chain synchronization that maintains inherited Ethereum security of
L2s.
In the stage of multi-chain synchronization, transaction sync hashes from secondary chains areforwarded to the primary chain via Ethereum L2s’ canonical message bridge. Upon the
successful verification of both ZKP and on-chain transaction consistency, batch root will besent to secondary chains via canonical message bridge for execution.
As the correctness of the states and transactions of L2s is finalized on Ethereum via validity
proof (for ZK-Rollup L2s) and fraud proof (for Optimistic-Rollup L2s), the additional multichain state synchronization is finalized via Ethereum. Thus, the zkLink Nexus L3 rollup inherits
the security of Ethereum.

Figure 3: zkLink Nexus Settlement Process

2.2.3 Origin: Settlement on Ethereum, Alt-L1s and L2s
In contrast to Nexus, zkLink Origin's architecture allows for the integration with Alt-L1s like
Solana and Avalanche, in addition to Ethereum and its L2s.

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A zkLink Origin rollup settles the transactions and transition of states on networks connected,
as long as one of the networks supports zk-SNARKs proof verification. To establish a fast andsecure communication mechanism between the alt-L1s and Ethereum, zkLink introduces aLight Oracle Network for cross-chain message transfer.
The security assumption of zkLink Origin is that the rollup sequencers, responsible for batchingtransactions, cannot collude with all nodes of the Light Oracle Network for malicious activities.

Figure 4: zkLink Origin Settlement Process

2.3 Execution Layer
Execution entails executing transactions that update the state correctly. Thus, execution mustensure that only valid transactions are executed, i.e., transactions that result in valid statemachine transitions.

2.3.1 TS-zkVM for Trading-Specific dApps
zkLink Trading-Specific-zkVM (TS-zkVM) is based on tailored core ZK circuits and Risc0
zkVM extension ZK circuits. The TS-zkVM offers high-throughput and low-cost execution for
App Rollup developers. It supports various order book product features, including but notlimited to spot trading, derivatives trading, NFT trading, etc.

2.3.2 zkEVM for Universal dApps
In zkLink’s modular architecture, developers have the flexibility to build their own customized
rollups based on open-sourced zkEVM frameworks like ZK Stack and Polygon CDK. Basedon zkLink aggregated rollup infrastructure, dApp developers can easily build Solidity written
app-rollups that have the access to the aggregated liquidity from multiple blockchains androllups.
Based on ZK Stack, zkLink has officially built zkLink Nova (refer to section 3.1), a
permissionless, aggregated zkEVM Layer 3 rollup for universal dApps. dApps can have accessto the aggregated liquidity from Ethereum and its L2 networks, while still inheriting the security
from Ethereum.
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2.4 Sequencing Layer
The sequencing layer is a pivotal component in rollup systems, primarily responsible forreceiving user transactions, sequencing the transactions and bundling them into batches. Thesebatches are then committed to the settlement layer. Additionally, in scenarios where the system
employs an external DA layer, the sequencer also ensures efficient transmission of transaction
data to the DA layer.
Similar to other rollups, zkLink starts with a centralized sequencer model. While this approach
offers certain development efficiencies, it also presents challenges and risks, such as potential
single point of failure, transaction censorship and issues around miner extractable value (MEV),
affecting network fairness and transparency.
To address these concerns, the zkLink protocol aims to incorporate decentralized sequencer
solutions. These solutions, including platforms like Espresso, Astria, and Fairblock, aim to
mitigate centralization risks by processing and validating transactions across a distributed node
network. This strategy will not only boost network security and transparency but also strive tooffer a more secure, equitable, and efficient rollup solution to its users.

2.5 DA Layer
Data Availability (DA) entails making the transaction data available. A DA layer is a criticalcomponent for rollups to ensure the capability to reconstruct the rollup states when the rollup
service halts unexpectedly.
Firstly, zkLink by default supports the primary chain as the DA layer.
Secondly, zkLink supports Validium mode, which involves an external DA solution. zkLink
will integrate various third party modular DA solutions, such as Celestia, EigenDA, Avail, etc.,
to meet diverse demands from developers.
Furthermore, zkLink DAO will have the option to organize a Data Availability Committee(DAC). This DAC serves as another option for developers, providing an additional choice fordata availability assurance.

3 zkLink Nova: The Industry’s First Aggregated Layer
3 Rollup Network
3.1 zkLink Nova Overview
7zkLink Nova is the industry’s first aggregated Layer 3 zkEVM Rollup network built on top of
Ethereum and Ethereum Layer 2 rollups (L2s). zkLink Nova, based on zkEVM of ZK Stack, isan EVM-compatible, open platform for simple and fast smart contract development of any kind.
zkLink Nova’s platform allows for scattered assets across Ethereum Layer 2s to be aggregatedfor interoperable transactions. zkLink Nova is secured by zero-knowledge proof technology,
charges extremely low gas costs, offers fast finality, and inherits its security from Ethereum
based on the zkLink Nexus solution.

Figure 5: zkLink Nova Aggregation Illustration

3.2 zkLink Nova Key Features
3.2.1 Native Asset Aggregation
Users can deposit assets from the Ethereum Layer 1 as well as Ethereum Layer 2s directly to
zkLink Nova. These assets will be locked inside the canonical rollup bridge contracts hostedon the source chains before entering the zkLink Nova network. This feature allows forapplications on Nova to have access to all the connected Layer 2s’ native tokens, thereby
allowing users to trade their multi-chain assets with interoperability.

3.2.2 Supporting Universal dApps
zkLink Nova is EVM-compatible by utilizing the zkEVM of ZK Stack. DApp developers candeploy any kind of Solidity smart contracts such as DEXs, Lending, GameFi, SocialFi and moreon Nova’s open platform. These dApps have immediate access to liquidity and native assets
from all the integrated networks, such as Arbitrum, zkSync, Linea, and many others.

3.2.3 Stack Agnostic to the Supported Networks
zkLink Nova is stack agnostic, meaning it can connect to rollups of different stack choices,
including ZK Rollups, Optimistic Rollups, and any additional stacks they’re built upon. While8this approach sacrifices the atomic interoperability of cross-rollup transactions, it offers thebroadest liquidity that can be aggregated from the entire Ethereum ecosystem.

3.2.4 Low Fees and High Scalability
zkLink Nova's modular stack provides maximal scalability for dApps building on top of theecosystem. ZK Stack is used by zkLink Nova as the execution layer, which dramaticallyreduces execution costs and provides a blazing-fast user experience. In Validium mode, anexternal DA solution will further reduce the data portion of transaction costs on the network forend users.

3.2.5 Ethereum Equivalent Security
zkLink Nova inherits Ethereum security by directly settling on Ethereum through the zkLink
Nexus settlement layer solution. Every transaction on Nova first undergoes verification via
zero-knowledge proof followed by multi-chain state synchronization via the canonical rollup
bridge. Sync hashes forwarded via canonical rollup bridges are used to check if the data
commitment for ZKP is consistent with the transactions on all host chains. This preventssecurity risk of a malicious node operator submitting false on-chain transactions.

Figure 6: zkLink Nova Transaction Life Cycle

4 zkLink X: The App-Specific Aggregated Rollup
Infrastructure
4.1 zkLink X Overview
zkLink X provides a modular infrastructure for aggregated App-Rollups with their own
sovereignty. Applications using zkLink X App-Rollup solution will be able to access the native
tokens across the connected L1s and L2s, allowing users to trade multi-chain assets on a unified
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user interface. Cross-chain asset bridges are not needed in the process, thus avoiding crosschain asset bridging risks and bridging fees.
zkLink X decouples the four layers of the rollup framework and provides a fast and customized
rollup deployment solution with SDKs and APIs. Developers have the freedom to choose whichbuilding blocks they need. zkLink X focuses on the development of settlement layer (Nexus
and Origin solutions) and execution layer (TS-zkVM) solutions, and will integrate third party
modular solutions for DA layer and sequencing layer, allowing developers to customize the key
components to meet diverse demands of different use cases.
-Network Integration and Settlement Layer Solution. Developers can choose which chains
the App Rollup can access to, including but not limited to: ETH, BNB Chain, Avalanche,
Polygon PoS, Solana, zkSync, Starknet, Scroll, Polygon zkEVM, Linea, Taiko, Arbitrum,
Optimism, Base, etc.
-Execution Environment: TS-zkVM, zkEVM-Decentralized Sequencer: Espresso, Astria, Fairblock, etc.
-Modular DA Solutions: In addition to Ethereum, developers can choose Celestia, EigenDA,
Avail, DAC organized by zkLink, etc.

4.2 Trading Specific zkVM for High Performance DEX
The TS-zkVM constructed by zkLink is a high-efficiency ZKP execution environment
specifically designed for high-performance financial products such as CLOB DEXs. TS-zkVM
extends and integrates with the risc0 zkVM outside of the precompiled core circuit.

Figure 7: TS-zkVM Architecture
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The above figure shows a high-level overview of the TS-zkVM architecture, which is divided
into three sub-layers.

4.2.1 Storage sub-layer of TS-zkVM
The storage of zkLink TS-zkVM utilizes a Sparse Merkle Tree (SMT) to store the state. Thisdata structure provides the system with an efficient and secure way to maintain and verifychanges in the state. Compared to the SMT in the EVM, the customized and optimized SMT ofzkLink TS-zkVM is more streamlined and better adapted to the needs of high-frequency
financial transaction scenarios. With in-depth customization, the SMT has been specificallytailored to suit particular business needs, thereby achieving exceptional zero-knowledge proof
performance.

4.2.2 Execution sub-layer of TS-zkVM
The execution sub-layer of TS-zkVM is divided into two parts, each designed for different
performance and scalability requirements:•

Precompiled circuit: Requires high performance and includes various transactionrelated circuits, such as:o Fund Related Circuits (Deposit, Withdrawal, Transfer)o Spot Trading Circuitso Derivatives Trading Circuitso Derivatives Management Circuits (Liquidation, ADL, Funding)o Oracle Verification Circuitso Authorization Circuits (Passkey Verification, Social Login Verification)
These circuits are specifically optimized to handle corresponding financial transactions,ensuring efficiency and high response speed when the system processes transactions.
Each sub-circuit corresponds to different types of transaction operations or financial
instruments and handles the most performance-intensive tasks.

•

Extension circuit: The extension circuit is built using risc0 zkVM on the same Sparse
Merkle Tree (SMT), and the proofs generated by the zkVM are subsequently verified
by the plonk aggregation circuit in the aggregation layer. Developers will be able toperform custom operations using risc0 zkVM, such as:o Grid Trading Circuitso Option Trading Circuitso Broker Trading Circuits
An SDK based on risc0 zkVM will be provided, which includes common operations
on the TS-zkVM SMT, such as: verifying a Merkle Tree Proof for a specific account,checking if the balance change of an account complies with certain patterns, etc.

4.2.3 ZK Proof Aggregation sub-layer of TS-zkVM
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The aggregation sub-layer is responsible for aggregating the different transaction proofs andproducing a proof to verify the correctness of the entire batch of transactions, which achieves
increased efficiency in proof verification and reduced on-chain costs for transactions.

Figure 8: Aggregation Detail of TS-zkVM
Aggregation Details
The aggregation sub-layer is composed of the following modules:
•

•

•

•

Precompile Module: This module includes trading-specified precompiled circuits,
which need to be compiled into verification keys (vk). This provides the system with aflexible way to generate customized circuits for specific types of transactions andintegrate them into the entire verification system.
SMT State Transition Circuit: The state transition circuit uses an SMT to record
states, with changes in the root representing all users' ledger changes, ensuring thecorrectness and consistency of the system state. Each state transition (S1, S2, S3, ...,Sn) is constrained by the circuit to generate a transition proof.
zkVM: This section demonstrates how to deploy zkLink Trading-DSL contracts using
risc0 zkVM to generate custom trading operations (op). This mechanism allows users
to customize trading logic and ensures that these logics are correctly executed andverified.
PLONK Aggregator: The PLONK aggregator is responsible for checking theconsistency of state transitions and the execution layer. It integrates proofs from12

•

different sources and generates an aggregated proof. This process enhances verification
efficiency and reduces the costs required for on-chain verification.
Proofs: The architecture includes various types of proofs:
o Precompile Proof: Ensures the correctness of the precompile layer.
o Transition Proof: Ensures the correctness of state transitions.
o zkVM Proof: Ensures the correctness of custom trading operations.

Interactions Between Modules••••

Application Specific Circuits are eventually compiled into verification keys, and theseverification keys are stored in the root node of the vk tree.
zkVM allows for the deployment of Trading-DSL contracts, generating custom
trading operations.
Precompiled circuits, risc0 zkVM, and SMT State Transition Circuits areinterconnected, ensuring the correctness of each state change.
All proofs are collected by the Aggregator and verified in the aggregation circuit — tocheck if the transition set commitment in the transition proof is included in the(Algorithm id, Input, Output) tuple vector of the precompile proof and zkVM proof,a membership proof verification is also needed in the aggregation circuit. Thisultimately produces an Aggregation Proof for on-chain verification.

5 Tokenomics
ZKL will be a standard ERC20 token issued on the Ethereum Mainnet. The total supply of ZKL
is capped at 1 billion and is non-inflationary. ZKL will also be made available on the zkLink
Nova network.
ZKL serves as the native utility token and governance token for the zkLink protocol.
Utility wise, ZKL helps developers unlock the access to the App-Rollup infra service of zkLink
X and pay for the zero-knowledge proof computational resource.
ZKL is the governance token of zkLink DAO, which governs the development of the protocol.
For zkLink Nova, in the future, ZKL will present the right to participate in Nova’s decentralized
sequencing network.

5.1 Payment
App Rollups served by the zkLink X solution will need to pay a license fee in ZKL to thezkLink DAO (the DAO). The DAO will provide support for startups with a certain amount of
ZKL, for covering license fees in the beginning. In return, the App Rollup will share a portionof its future revenue or tokens with the DAO.

13ZKL is the payment token for the zero-knowledge proof generation service provided by provers.
Provers bid in zkLink’s proof auction market and complete the proving tasks to earn ZKL
tokens. Provers will need to stake a specific amount of ZKL to join the proof market. The
provers that fail to complete a task or exceed the time requirement will be punished. This
dynamic mechanism fosters competition and motivates provers to continuously improve theirservices and contribute to the entire zkLink ecosystem.

5.2 GovernanceZKL is the governance token of zkLink protocol. Holders will be able to stake ZKL to get
veZKL based on staking amounts and the remaining lock-up period. veZKL holders will
exercise governance rights over the direction and development of zkLink DAO.
Today, zkLink Nova’s revenue comes directly from the centralized sequencer, accruing to thezkLink DAO vault. In the future, ZKL grants the right to participate in zkLink Nova’s
decentralized sequencing network.

5.3 Optional Gas Token of zkLink Nova Network
The native gas token of zkLink Nova is ETH. However, users will have the option to pay thegas cost in ZKL at a discount rate when conducting transactions on Nova.

6 Conclusion
This paper presents the conceptual design and system structure of zkLink protocol, adecentralized aggregated rollup infrastructure protocol based on zero knowledge technology.
zkLink addresses the problems of liquidity fragmentation, lack of interoperability, high trading
cost, and complexity of multi-chain deployment via a novel aggregated rollup framework using
zk-SNARKs technology with multi-chain state synchronization.
Based on zkLink aggregated rollup infrastructure, zkLink Nova is built to be the industry’s first
aggregated Layer 3 zkEVM Rollup network for general purpose dApps, enabling developers
and users the access to the aggregated liquidity from the entire Ethereum ecosystem, including
Ethereum, ZK-Rollups and Optimistic Rollups.
For customized high-performance applications requiring their own sovereignty, zkLink X
serves as a middle-ware infrastructure that abstract away the complexity of multi-chain
deployment, making developers feel like building on a single chain with multi-chain liquidity
with SDK and APIs. Its modular architecture allows developers to customize the key
components to meet diverse demands in different use cases. The TS-zkVM provides a highefficiency execution environment specifically designed for high performance and low-cost
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financial products such as CLOB DEX, NFT trading etc., contributing to the mass adoption ofself-custodial, user-friendly DeFi products.

Glossary
ZKP
Zero-knowledge Proof
L1
A layer 1 blockchain such as Ethereum, Solana, Avalanche, BNB Chain, etc.
L2
A Ethereum layer 2 rollup network such as zkSync, Starknet, Arbitrum, Optimism, etc.
L3
A rollup network built upon L2.
TS-zkVM
A trading-specific execution runtime based on tailored low level core ZK circuits and opensource zkVM extension circuits, developed by zkLink.
zkLink Nexus
A multi-rollup Layer3 ZK-Rollup architecture proposed by zkLink, which connects EthereumL2s.
zkLink Origin
A multi-chain ZK-Rollup architecture proposed by zkLink, which connects various L1s andL2s.
zkLink App Rollup
An application-specific rollup network based on the rollup infra solution provided by zkLink,
deployed by developers that need high throughput and low transaction cost, for example, orderbook exchanges.

15References
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4.
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https://docs.celestia.org/developers/build-modular
https://docs.espressosys.com/sequencer/espresso-sequencer-architecture/readme
https://docs.polygon.technology/cdk/
https://docs.zklink.io/
https://docs.zk.link/
https://era.zksync.io/zk-stack
https://layerzero.network/publications/LayerZero_Whitepaper_V2.0.pdf

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