COZ Protocol: Cross-chain Synchronizer based on ZK-Rollup
Coz Protocol is a universal layer which synchronizes states between multi-chain smart contracts. Current cross-chain synchronization has two major challenges. First, contracts from different main blockchains cannot communicate with each other, which makes it hard to establish a trustworthy communication channel to share and maintain a universal state between each other. Second, transactions on different blockchains can hardly be ordered so a novel way is needed to avoid and handle the conflicts. Coz Protocol is a ZK-Rollup based multi-blockchain synchronizer on top of which rich cross-chain applications can run safely and efficiently.
As a new distributed computing paradigm, blockchain is rapidly evolving in areas such as decentralized finance and cryptocurrency. However, existing blockchain projects adopt different blockchain architectures and protocols, which results in the difficulty for value flow and communication between each other. Different blockchain systems have become isolated islands that brought limitations to the usable range, function and scalability for blockchain technology. In order to build trust between different blockchain networks, cross-chain technology has been proposed and received vast attention. Below are some previous cross-chain solutions:
The main idea of notary schemes is to elect one or more trusted nodes as a notary public and verify transactions in different blockchain networks through notaries which can also prove to the nodes in the other blockchains. Therefore, the data exchange between different blockchains is completely managed by notaries. However, the notary scheme does not only rely on a single entity; it can be divided into Centralized Notary Schemes and multi-sig Notary Schemes. Current cross-chain projects using the notary scheme include Corda launched by R2 and The Interledger Protocol (ILP) proposed by Ripple Lab. The centralized notary schemes can reach high operation and processing efficiency but suffer from single point failure problems. Therefore, a multi-sig notary scheme has been proposed to reduce the centralized problem. However, this multi-sig notary scheme can only act as a temporary transition plan since it still has potential evil risks.
A 2-way peg (2WP) allows the transaction of assets from one blockchain to another and vice-versa. The assets are not transferred technically but temporarily locked on the source blockchain while the same number of tokens are released in the target blockchain. The transferred asset can be withdrawn when the equivalent number of tokens on the target blockchain is locked again. The problem with this scheme is that the transaction is not completed until the target blockchain has released the equivalent amount of assets. Therefore，any 2WP system must compromise and rely on assumptions of the honesty of the actors involved in the 2WP.
The concept of a sidechain was first proposed in 2014. The main goal of the sidechain is to extend the scalability and functionality of the blockchain system. When using a sidechain as a trusted centralized entity in a 2WP system, it can be used as a standalone transaction dealer. The sidechain can enforce the security of transactions by implementing a consensus-validated protocol. Since a sidechain needs to update state changes back to the underlying blockchains, the blockchains need to trust or verify the transactions sent out by sidechains. Usually, the cost of trust (a vulnerable sidechain) or verification (gas fee) is very high.
Cross Chain Gateway and relays
Blockchain relay schemes verify transactions across blockchains in a decentralized manner. While this enables blockchain interoperability applications like cross-blockchain token transactions, relays can become expensive since state-of-the-art relays require every single block header of the source blockchain to be stored by the destination blockchain.