Future Development Directions of Cross-Chain Services

In recent years, numerous independent public chains and Ethereum Layer 2 solutions have emerged in the blockchain field. Due to differences in security, cost, transaction speed, and developer and user communities across chains, users often need to switch between different chains. Compared to the Ethereum mainnet, Layer 2 and other independent public chains usually offer lower fees and faster transaction speeds. Therefore, users have to rely on cross-chain bridge services to reduce transaction costs or to use high-quality applications on other chains.

If we compare cross-chain bridges to "armored trucks," then regardless of the threats faced, the armored truck itself must possess strong defensive capabilities, without any security risks. Every stage from design, production to operation must be error-free. However, the cross-chain bridge solutions currently available on the market have, to varying degrees, architectural design flaws, code vulnerabilities, or rely on certain trust assumptions during the sending, receiving, and relaying processes, all of which greatly diminish the security of cross-chain bridges.

As a bridge connecting various public chains, cross-chain bridges not only solve the problem of liquidity fragmentation between public chains but also serve as a key solution for asset cross-chain transfer. However, user demand for cross-chain technology is not limited to asset cross-chain; this is merely one application of the entire cross-chain protocol in the DeFi field. Through cross-chain protocols, two completely different networks achieve interoperability, which not only requires the transfer of tokens between independent platforms but should also support inter-chain communication of large files and data packets.

In the Web3.0 multi-chain ecosystem, the ideal scenario for users is to interact with all mainstream public chains for asset and data exchange through a single application, without the need to frequently switch wallets and networks. In the current landscape of "one dominant and many strong" public chains, users urgently need a more secure, more versatile, and more user-friendly cross-chain communication protocol.

Mainstream Cross-Chain Communication Models

native verification mode

The native verification mode operates lightweight clients in the virtual machines of both the source chain and the target chain, facilitating inter-chain communication through relayers. The advantage of this mode is that it does not require the operation of an additional intermediary chain. If zero-knowledge proof technology is employed, as in certain projects, it can also avoid the trust assumptions required by other solutions.

external verification mode

The external verification model relies on one or a group of validators monitoring specific addresses on the source chain. When a user sends assets to that address, the assets are temporarily locked. Third-party validators need to verify this information and reach a consensus. Once consensus is reached, the corresponding assets will be generated on the target chain.

The disadvantage of this communication model is the existence of a "trust assumption," which can easily lead to asset theft due to "single points of failure" or "local failures."

local verification mode

Local validation is a peer-to-peer liquidity network. Each node acts as a "router", providing the native assets of the target chain instead of derivative assets.

The limitation of this model lies in the lack of "universality"; it is only applicable for cross-chain asset transfer and cannot achieve inter-chain transmission of general information and data.

upstream chain model

The upstream chain requires the dApp to deploy smart contracts on its chain so that messages can be copied and sent to other Layer 1 public chains for state updates.

The main disadvantage of this model lies in the business realm, where the upstream chain will compete with all Layer 1 chains rather than collaborate, as all parties are vying for dApps to be deployed on their own chains.

zkRelayer: The Key to Cross-Chain Communication

An outstanding cross-chain communication solution should possess the following characteristics:

• Trustless assumption, secure and reliable
• Permissionless, decentralized
• Highly versatile
• Good scalability
• Fast, low cost

However, not all cross-chain solutions can meet these conditions simultaneously, and the importance of each feature varies. Users may be able to accept relatively slower or more expensive cross-chain services, and they may not necessarily need immediate support for various data formats in cross-chain transfers. However, the "no trust assumption" is urgent and important.

The early external verification model attempted to solve the communication problems of other public chains with a single chain, which from a methodological perspective is a rather cumbersome approach. It is difficult to address the communication issues between EVM and non-EVM, as well as between PoW and PoS chains. At the same time, the intermediary chain itself is a singular centralized tool, making it hard to "prove its own innocence," as it lacks decentralized security and has no trustless security.

Some solutions in native verification mainly emphasize the roles of the sender and receiver clients, downplaying the importance of relays and oracles. There are several issues here: first, users must trust that relays and oracles will not collude for malicious purposes; second, users must also trust that the protocol itself will not act maliciously in the relay stage. In other words, current solutions cannot achieve true trustless security. Single points of failure and local failures are like a ticking time bomb, lurking in cross-chain communication solutions that have inherent flaws.

zkRelayer is a new type of zero-knowledge proof relay for cross-chain communication, whose greatest advantage lies in the fact that users do not need to trust any external third parties, nor do they need to trust the protocol itself. As long as the mathematical and cryptographic proof process is complete and correct, this system can gain public recognition. It is worth noting that a fundamental change has occurred here: users trust "truth," not any individual or organization. Individuals or organizations may make mistakes or act maliciously, but truth never does.

In the entire communication link (Chain A → Sender → zkRelayer → ZK Validator → Receiver → Chain B), the position of the zkRelayer will surpass that of the two light clients, the Sender and the Receiver, becoming the core of the entire solution.

The core components of zkRelayer include ZK provers and message aggregators. Some projects adopt zero-knowledge proof methods that have characteristics such as fast, recursive, and trustless, with linear proof time and sublinear verification time reaching theoretical limits. Applying this technology to relays for cross-chain communication will ensure that the entire communication process is trustless, efficient, and low-cost.

zkRelayer is expected to be the key to opening a new chapter in cross-chain communication. With its support, cross-chain communication technology will usher in revolutionary development.