Blockchain technology has penetrated into different industries and scenarios such as finance and supply chain, effectively breaking the value islands between different participants in the same scenario. However, at this stage, it is difficult for value to flow between different industries and different scenarios. This makes the participants of different blockchains become small closed groups, which is obviously not conducive to the social circulation of value. Therefore, it is imperative to realize the interoperability of the blockchain. At present, the interoperability of blockchain is mainly realized through cross-chain technology. According to specific technical routes, cross-chain technology can be divided into four categories: notary technology, side-chain technology, atomic exchange technology, and distributed private key control technology.
(1) Notary public technology
In the notary technology, transaction participants select a group of credible notaries in advance to ensure the effective execution of the transaction. The InterLedger protocol proposed by Ripple is a typical case of notary technology. InterLedger realizes cross-blockchain transfers. Before the sender of the A chain transfers to the receiver of the B chain, it needs to find a set of connectors, and the linkers send funds to the receiver hop by hop. Each linker needs to appoint a group of notaries, and the notaries shall supervise the validity of this group of transactions.
The main problem of notary technology is the need to trust a specific group of notaries, which violates the original intention of the blockchain decentralization design and introduces certain security risks.
(2) Side chain technology
With the help of side chain technology, one blockchain can read and verify the events and status of other blockchains. At present, side chain technologies can be divided into two categories: a pair of side chains and star side chains. One-to-one side chain technology includes new blockchains represented by BTC Relay and RSK. This type of blockchain can interact with an existing blockchain (such as Bitcoin), and the main purpose is to realize the functional expansion of the existing blockchain. The star-shaped side chain technology mainly includes cross-chain infrastructure represented by Polkadot and Cosmos, which connects multiple other blockchains by constructing a new blockchain to form a star topology to realize inter-blockchain communication. Value and information flow.
(3) Atomic swap
The basic idea of atomic swap is that when the two parties on the two chains exchange assets, the two parties in the transaction maintain a mutually restrictive trigger through technologies such as smart contracts to ensure the atomicity of asset exchange. That is, the asset exchange between A and B occurs at the same time or does not occur at the same time, and the transfer of A to B is completed, but B does not transfer to A.
A typical case of such cross-chain solutions is Blocknet. On the basis of atomic swap, Blocknet has added functions such as order matching and transaction matching to realize decentralized cross-chain currency exchange. However, the application scope of atomic swap technology is relatively narrow, limited to the field of cross-chain transfer, and cannot meet other cross-chain requirements.
(4) Distributed private key control technology
Distributed private key control technology aims to map various digital assets to a new blockchain through distributed private key generation and control technology, so as to realize the free exchange of different digital assets on the same blockchain.
Fusion is a representative project of distributed private key control technology. Its core idea maps the digital assets on each blockchain to the public blockchain built by Fusion. In simple terms, just like different blockchain users depositing digital assets in the "bank", the digital assets in the bank can be freely circulated and exchanged, and the user account balance can be updated in real time. The account balance shall prevail.
Distributed private key control technology is similar to atomic exchange technology, and can only complete cross-chain asset transfer, and cannot yet perform more complex cross-chain interoperability. If the function cannot be further expanded in the future, the application scope of distributed private key control technology will be far from the expected effect.
It can be seen that there are obvious shortcomings in existing blockchain interoperability solutions. First, the application range is narrow. For example, BTC Relay can only complete one-way operations from Bitcoin to Ethereum, while InterLedger and Fusion can only complete cross-chain transfers and cannot perform other types of operations. Second, the compatibility is poor. For example, systems such as Cosmos only support the interconnection of blockchains with the same structure. In short, the existing cross-chain and interoperability solutions are still in their infancy, and there is still a long way to go before practical applications. Optimizing for such problems is also the future evolution direction of blockchain interoperability. In addition, the interoperability research of blockchain is directly related to the interface standard of blockchain communication. However, the most influential cross-chain solutions are currently proposed by foreign companies and research institutions. When designing cross-chain solutions, relevant entities will first consider their own economic interests. Therefore, my country should promote the research of blockchain interoperability as soon as possible, and actively participate in the formulation of cross-chain standards, so as to gain more voice for the domestic blockchain industry.