Polkadot - EVM Bridge
Introducing ZKLiquid
ZKLiquid is a cross-chain liquidity protocol and interoperability oracle network that provides siloed blockchains with a decentralized and secure means to transmit on-chain assets and sync data, thereby facilitating interoperability between these blockchains.
The primary goal of ZKLiquid is to create a reliable and secure EVM-nonEVM interoperability network. This involves developing an EVM-Polkadot/Kusama decentralized relay network and liquidity bridging protocol to enable seamless interoperability between numerous EVM blockchains and the Polkadot/Kusama ecosystem.
The team's motivation for building ZKLiquid stems from the lack of robust cross-chain interoperability solutions connecting EVM chains to the Polkadot/Kusama ecosystem. While there are many protocols for EVM-to-EVM interoperability, there is a significant gap in scalable, default interoperability solutions for EVM to Polkadot/Kusama. This gap limits the ability of projects within these ecosystems to integrate and leverage cross-chain technology for growth.
Interoperability frameworks must prioritize security. In 2022, over $2 billion worth of crypto assets were lost due to exploits in interoperability protocols that relied on centralized infrastructure. Such centralized solutions introduce single points of failure, making them prime targets for attackers aiming to tamper with cross-chain data.
This security challenge further motivates the team to build ZKLiquid; a scalable, secure EVM-Polkadot/Kusama interoperability network and liquidity protocol. This solution aims to securely facilitate interoperability between numerous EVM chains and Polkadot/Kusama parachains, facilitating growth of the ecosystem.
The technical details and architecture of ZKLiquid is as follows
Core Components of ZKLiquid
The core components of ZKLiquid infrastructure and technology are the ZKLiquid EVM Blockchain (zklEVM), a parachain on Polkadot/Kusama, and the ZKLiquid Interoperability Oracle Network (ZION), a decentralized oracle network that facilitates the secure transmission of data between EVM blockchains and the Polkadot/Kusama ecosystem. These components make up the main infrastructure of ZKLiquid and facilitate its primary functionalities. A brief overview of these components is presented below:
1. ZKLiquid EVM (zklEVM) Blockchain
zklEVM is a fully EVM-compatible blockchain (parathread) on Polkadot/Kusama, designed to become a parachain. It implements both the EVM pallet by Frontier and the XCM pallet, among others. This combination allows zklEVM to support Ethereum-compatible smart contracts while also enabling cross-chain communication with other parachains within the Polkadot/Kusama ecosystem.
With this capability, data on zklEVM can be seamlessly transmitted within the Polkadot/Kusama ecosystem, allowing dApps developed and deployed on zklEVM to inherit the interoperability of the Polkadot network. This enables them to interoperate with all other parachains, facilitating a broader range of decentralized applications and use cases across the Polkadot/Kusama networks.
In addition, as a future parachain of Polkadot, zklEVM leverages the robust security model of Polkadot's relay chain. This includes shared security, where the consensus and security of zklEVM are backed by the entire Polkadot network. This setup enhances the trustworthiness and resilience of smart contracts deployed on zklEVM, as they benefit from Polkadot's decentralized validation and governance mechanisms.
2. ZKLiquid Interoperability Oracle Network (ZION)
The ZKLiquid Interoperability Oracle Network (ZION) is a decentralized oracle network (DON) that facilitates the transmission of data and assets between any EVM blockchain (non-Polkadot) and zklEVM, as well as other parachains on Polkadot/Kusama. ZION consists of several oracle nodes that sync data from a source chain and then transmit it to the destination chain, where on-chain validation of the transmitted data is performed.
Additionally, ZION implements a proof-of-stake-like consensus and slashing mechanism, ensuring that each oracle node has vested interest in the overall security of the network and nodes with malicious intentions are punished through stake slashing, maintaining the integrity and reliability of the network.
While the primary functionality of ZION is the transmission of data from EVM blockchains (non-Polkadot) to zklEVM and other EVM-compatible parachains, the data can then be transmitted to any non-EVM-compatible parachain via XCM, thus expanding the communication capabilities of parachains to include EVM blockchains.
Technical Architecture and Detail of ZION
The main technology the facilitates the interoperability of Polkadot/Kusama on ZKLiquid is the ZKLiquid Interoperability Oracle Network (ZION). ZION is a decentralized oracle network (DON), essentially a decentralized system of oracle nodes that uses a proof of stake-like (PoS) consensus mechanism to validate and sync transaction/state data between Polkadot/Kusama parachains and EVM chains, facilitating secure interoperability between the Polkadot/Kusama ecosystem and EVM chains.
ZION Security Considerations
To ensure the secure and tamper-proof transmission of data between chains, ZION implements several security mechanism and measures, these includes:
Decentralization and Oracle Nodes: The oracle network is secured by multiple oracle nodes, with a minimum requirement of 20 nodes transmitting and validating data. This high number of validators ensures decentralization, significantly reducing the risk of a 51% attack.
On-chain Validation of Data: With combined decentralized aggregation of data by multiple oracle nodes, ZION validates the accuracy and integrity of data aggregated from the nodes directly on-chain before it is used in smart contracts.
Staking Requirements: Oracle nodes are required to stake DOT tokens. The amount required to become an oracle node validating data must exceed a specified minimum stake, ensuring that validators of transmitted data have a vested interest in the network's integrity.
Penalization via Stake Slashing: Oracle nodes that misbehave or act maliciously are penalized through stake slashing. This means that a misbehaving node will lose a portion of its staked tokens as a penalty, deterring dishonest actions.
Random and Proportional Selection of Executor Node: To ensure security and fairness, the selection of the node (executor) that executes a finalized data is both random and proportional to the amount of DOT staked. For example, if Node A has 1000 DOT staked and Node B has 3000 DOT staked, Node B has three times the chance of being selected as the forger compared to Node A. However, the selection process remains fundamentally random.
By implementing these security measures, ZION ensures robust, decentralized, and secure interoperability between the Polkadot/Kusama ecosystem and EVM chains.
Functional Components of ZION
ZION has two main independent, decentralized oracle network, these are:
Data Transmission DON
The Data Transmission DON (Decentralized Oracle Network) is a group of oracle nodes responsible for transmitting data/state values between source and destination chains. These nodes do not perform any state changes themselves; instead, they contribute to the pool of aggregated data that will be validated on-chain consensus oracle contract.
The above shows a more detailed schematic of ZION with components that participates in data validation.
Execution DON
The Execution DON consists of nodes responsible for executing data/state upkeeps based on incoming data from the destination chain. These nodes also validate the incoming data on the source chain against the validation provided by the Transmission DON before executing the state upkeep.
By separating responsibilities between the Data transmission DON and the Execution DON, ZION ensures efficient and secure data transfer and state updates across blockchain networks.
A high level architecture of ZION connecting a bridge on an EVM chain to Polkadot/Kusama is as follows:
How it works
When crypto assets are sent from an EVM chain (source) to a Polkadot parachain (destination), the process of transferring the asset is as follows:
Asset Locking: The token sent is locked in the bridge liquidity pool on the source chain. This action ensures that the asset is securely held and cannot be double-spent during the transfer process.
Data Transmission and Validation: Validators within the decentralized Data Transmission Decentralized Oracle Network (DON) receive the data regarding the locked token. This network is responsible for securely transmitting and validating transaction data across chains.
Finality and Data Availability: After data validation finality is reached on the source chain, the transfer data—which includes the token address on the destination chain, the amount, and the recipient's address—is securely transmitted and made available to the destination chain. This ensures that the transaction details are accurate and immutable.
Execution and State Update: The execution process then updates the state of the bridge liquidity pool on the source chain to reflect the locked asset. The corresponding tokens are minted or unlocked on the destination chain and transferred to the recipient's address. This final step involves performing an upkeep operation to ensure the accurate and secure transfer of assets.
This decentralized and secure approach ensures that asset transfers are conducted without a single point of failure, enhancing the security and reliability of the cross-chain bridge.
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