Original title: "Bitcoin Network Cross-Chain Message Transmission Protocol Based on zkBridge"
Original source: Polyhedra Network
Polyhedra Network has launched a zkBridge-based Bitcoin cross-chain messaging protocol to significantly improve the interoperability of the Bitcoin network. This innovation aims to enable the Bitcoin network to efficiently and securely interoperate with other layer-1 and layer-2 blockchain networks.
Bitcoin Network as a Sending Chain: Trustless access to any data and protocol on the Bitcoin network using zkBridge
In order to promote interoperability between Bitcoin and other blockchain networks, it is essential to implement a cross-chain protocol in which the Bitcoin network acts as both a sending chain and a receiving chain. In the direction where the Bitcoin network acts as a sending chain, the Bitcoin network is fully compatible with the Polyhedra Network's zkBridge framework. zkBridge enables the updater contract (i.e., light client contract) on the receiving chain to directly verify Bitcoin's consensus mechanism and verify each transaction on Bitcoin by verifying the Merkle proof. This compatibility ensures that zkBridge can fully cover the Bitcoin network's PoW consensus proof and each transaction Merkle proof.
The Bitcoin network’s zkBridge significantly enhances the interoperability of the Bitcoin ecosystem. Our zkBridge system allows the transfer of all current and historical data on Bitcoin to any layer-1 and layer-2 blockchain network (such as Ethereum, BNB Chain and Arbitrum) as well as any app. Our solution is also compatible with the latest innovative protocols on the Bitcoin network such as Ordinals, BRC-20, Atomics, etc. This enables smart contracts on other blockchain networks to access any data and protocols on the Bitcoin network without trust and implement various computing logic. System security is guaranteed by the zero-knowledge proof system.
The Bitcoin network as a receiving chain: writing data from other chains to the Bitcoin network through a decentralized and crypto-economic trust model
The Bitcoin network interoperability protocol based on zkBridge can significantly optimize the interoperability of the Bitcoin network and enhance the security of the overall blockchain world. However, when transferring messages and assets from other blockchains to the Bitcoin network across chains, we will face a major challenge: the Bitcoin network lacks support for native smart contract functionality. Therefore, the Bitcoin network cannot serve as a standard zkBridge receiving chain because we cannot build a light client contract on the Bitcoin network to verify the status of the sending chain. Therefore, we need new models that can allow data from other blockchains to be safely written into the Bitcoin network. In order to simplify the following discussion, in this article, we will use Ethereum as the representative sending chain and Bitcoin as the receiving chain to explore how we transmit data from other chains to the Bitcoin network.
Diagram: Safely writing data from Ethereum to the Bitcoin network
To ensure the security of these cross-chain transactions, we use a mechanism similar to Proof of Stake (PoS). This involves inviting validators to stake Ethereum native ETH tokens. If the sending chain is the BNB chain, then the validators need to stake BNB tokens. These staked owners are then authorized to write data on the Bitcoin network. In order to reach a consensus on the correct message sending, these validators will use the Multi-Party Secure Computation (MPC) protocol. It is worth noting that the use of the MPC protocol is intended to enhance the robustness and reliability of our protocol.
The core feature of our proposal is that the security of our protocol does not rely on the accuracy of the multi-party secure computation (MPC) protocol. Even in the case where a malicious entity controls a majority of the MPC protocol members and tampered with the correct information, our protocol can still provide sufficient security for users. If a malicious entity controls the MPC protocol, the user can automatically initiate a zkBridge request to send the malicious message written to the Bitcoin network from the Bitcoin network to Ethereum and verify it through zkBridge. After receiving the message, the slashing contract on Ethereum will evaluate its validity (i.e. verify whether the message is really a malicious message) and impose a slash on the MPC committee if necessary. Part of the slashed staked funds will then be compensated to the users who suffered losses. By introducing decentralization and cryptoeconomic trust based on the staking/re-staking mechanism, our solution ensures that user assets are still sufficiently safe in the presence of potential illegal behavior in the MPC protocol, thus ensuring that data from any blockchain network can be securely written to the Bitcoin network through the zkBridge protocol.
Our detailed plan is as follows:
1. Stakers initially deposit ETH tokens on Ethereum as collateral.
2. In this case, if a staker behaves maliciously, any honest staker or user can report this fraud on Ethereum. We then use zkBridge to pass the relevant data written on the Bitcoin network to Ethereum. . In particular, as mentioned above, the one-way zkBridge structure with Bitcoin as the sending chain is very simple. Our zkBridge includes a decentralized zero-knowledge proof generation network. Any node in the network can pass the current block header of the Bitcoin network and its zero-knowledge proof to Ethereum. Ethereum can then use these block headers to verify any cross-chain transactions that appear on the Bitcoin network.
3. At the same time, there is a dedicated smart contract on Ethereum that is ready to automatically verify the validity of messages transmitted from the Bitcoin network. Once a malicious message is discovered and confirmed, the contract will automatically execute the operation of slashing the ETH deposit of the dishonest pledger.
4. This ensures that as long as at least one committee member or one user on the Bitcoin network remains honest, our staking mechanism remains secure, trustless, and decentralized.
Essentially, the staking/re-staking mechanism we introduced not only enhances the utility of Bitcoin, but also strengthens the trust and security between Proof-of-Stake (PoS) blockchains, marking a major step forward in the field of digital assets and decentralized finance.
Summarize
In summary, the Bitcoin interoperability protocol introduced by Polyhedra Network marks a major leap forward in blockchain technology. By enabling the Bitcoin network to act as both a sender and a receiver, combined with zkBridge, our interoperability protocol paves the way for unprecedented interaction between Bitcoin and various blockchain networks. For the case where the Bitcoin network is the sending chain, zkBridge allows all current and historical data on the Bitcoin network to be transferred to any layer-1 and layer-2 blockchain network without trust. For the case where the Bitcoin network is the receiving chain, our system not only ensures strong security through staking and slashing mechanisms, but also enhances the utility and reach of Bitcoin. This innovation not only taps into the potential of idle Bitcoin, but also strengthens trust and security between proof-of-stake blockchains, heralding a new era of digital assets and decentralized finance integrated into the Bitcoin ecosystem.
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