Author: Qingzhou
Today, we can see that many public chains are using multi-chain structures, such as cross-chain projects Polkadot and COSMOS, such as Ethereum’s sharding (old roadmap) structure. From a technical logic point of view, the multi-chain structure exists in many ecosystems. As long as the process of communication between different layers and different chains (or nodes) is involved, some design on the multi-chain structure is required.
In this article, we will take a look at a very important part of the multi-chain design, mutual protection of security.
Mutual protection of PoW chains
Plan Bai had seen some security protection solutions in the early days. At that time, when the industry focus did not focus on the PoS network (Ethereum), the cryptocurrency industry still highly respected the security brought by PoW. .
In the past few years, there have been many incidents of PoW network attacks. The reason for this is related to the computing power of the PoW network. The computing power in the consensus process of the PoW network is also one of the determining factors, which is what we call 51% computing power attacks. , When you have more than 51% of the computing power, you can generate an attack chain to replace the original longest chain.
Here, the attacker used rented or own computing power to attack the network. This is very common for many networks where the total computing power is not high and the computing power is not scattered enough. For example, the ETC network that is in the problem of client changes, and the BTG network that has insufficient computing power.
Therefore, we can think about how a PoW network with very low computing power can improve the security of its own network without changing the network structure, consensus algorithm, and causing forks.
Here you can choose the idea of seeking protection. For a low computing power blockchain, you can use a high computing power blockchain for protection. It is very simple to understand. The low-computing power blockchain believes that the high-computing power blockchain has a sufficiently high and decentralized computing power, and has higher security.
The picture shows the structural design case of using BTC network to protect BTG network
The security of the low-power blockchain is not high because it is prone to double spending of the ledger, so if the ledger of the low-power blockchain is packaged into the high-power blockchain through cryptography and communication protocols In the block, there is a fair proof just outside the own blockchain. This proof can reversely prove whether the data of the original blockchain is correct.
This is the idea of a high-computing power blockchain sharing its security with a low-computing power blockchain, because the blockchain itself is a distributed proof system, as long as it conforms to the idea of safe proof, it can be Security, many networks that lack security or require higher security can obtain security through this proof method (for example, some networks that have just been created).
In addition to PoW chains that need to be protected due to low computing power, in the multi-chain structure, there are many “copy proof” processes, so the protection relationship widely exists in the multi-chain design.
Those multi-chain structures with protective relationships
Why is there a multi-chain structure? The fundamental reason still needs to rely on the multi-chain structure to solve the problems that a blockchain cannot solve, that is, capacity expansion, data sharing, security, etc.
In the multi-chain design, security is still the core, because the biggest highlight of the blockchain is to solve the double-spending problem.
Many of the cases we have seen that are designed as multi-chain are based on security.
For example, the most commonly seen design: anchor currency, anchor currency is a good design for liquid assets on a network with higher performance, and anchor currency is the result of a single asset being protected by another chain.
This design may not be obvious to understand, because, for example, Ethereum does not use the security of the Bitcoin network, but Bitcoin uses the Ethereum network to increase the liquidity of assets.
We take this idea to a clear deduction. When chain a needs to generate blocks from chain b to confirm the security of information on chain a, chain b is protecting chain a. In this structure, the a chain will also generate its own data, but the data in the b chain block chain has the ability to prove.
The picture shows the multi-chain structure of Polkadot
For this structure, we can use Polkadot’s relay chain, COSMOS’ Zone chain, the bridge of the cross-chain solution to HUB, the design of the Ethereum beacon chain and sharding, and the plasma side chain.
Their common feature is this: the lower chain relies on the upper chain to confirm the final ledger, and the next chain needs the upper chain to prove itself that the data on the chain is correct.
When your own chain has a consensus, your own chain can operate safely and independently. When you need to obtain some proof, you can get the correct information from the upper chain.
Security protection structure of cross-chain relay
The COSMOS fire in 2019 and the Polkadot fire in 2020 are both cross-chain projects, and the ecology of both projects is a multi-chain structure. In the multi-chain structure, the ultimate security is the mainnet of the two projects. COSMOS is the COSMOS HUB, and Polkadot is the Polkadot mainnet.
For the chain connected in the Polkadot ecology and the COSMOS ecology, both need to rely on the security of the main network, and this security is reflected in the chain and the relay part of the main network. COSMOS is Zone, and Polkadot is the relay chain.
The role of Polkadot relay chain and Zone is the same. They are both a transit and security proof part of the communication between the chain and the chain.
The first thing to say is that the relay part is the part responsible for information transmission. The simplest model is the gateway, which is mainly the function of information transmission and translation. After the upgrade, it is the relay node to perform the information communication process. Once you have your own ledger and consensus, you will have higher security. It can be a part of protecting other chains.
The picture shows the chain structure of COSMOS
In COSMOS and Polkadot, the relay level is very high, because the relay nodes are all part of the main network nodes, and the data synchronized by the full nodes is the chain’s general ledger. The nodes of the relay also include the nodes of the lower chain, that is, the ledgers of the lower chain and the relay chain are also synchronized. The consensus of the relay chain protects the security of the ledger of the lower chain, and the lower chain also participates in the consensus process of the relay chain.
Particularity of side chain or layer2
The existence of relay is in a cross-chain structure that is indeed a multi-chain, and in the structure of the only main network in the ecology like Ethereum, all other chains are forked Ethereum, or through a node Synchronize the data of Ethereum and use the data security of the Ethereum main network.
This approach is common in side chains.
This structure means that the transaction and contract operation processes are all on the side chain, and the transaction structure is on the chain, and the resulting data is packaged by the Ethereum main network and becomes a security proof.
In the usual introduction of the side chain, it will be introduced that the side chain relies on the main network to provide security. Even if the side chain itself has a consensus, the side chain itself will exist when the main network data synchronization is required, that is, the side chain The data source is not credible, and only the data packaged in the Ethereum block or the data after collaboration through the Ethereum node can be trusted.
The picture shows the technical structure of the Ethereum sidechain solution Matic
For example, if Defi is running on the side chain, the data of ERC20 tokens and the token price on DEX are all based on the data on the Ethereum chain.
The side chain is a type of Layer 2, and the wide range of layer 2 solutions does require the main network to provide security, that is, to provide data confirmation and generate on-chain proofs. There is a logic here that the existence of layer2 is to expand the main network. Therefore, whether the layer2 network is an independent network and whether there is consensus is not the main design goal, because many layer2 solutions have no chain, only smart contracts.
Therefore, our topic today is the protection relationship between the chain and the chain. The layer2 solution that has been made into its own chain will meet the scope of today’s discussion, because it needs the security of the main network.
Ethereum’s sharding and other layered designs
In addition to other designs, the current understanding of inter-chain protection, in fact, the sharding structure of Ethereum 2.0 is very obvious.
From a structural analysis, sharding is a manifestation of the main chain and sub-chain structure. In this structure, the main chain is responsible for the final confirmation, and the main chain is naturally responsible for security.
In the future, when the beacon chain is responsible for the block confirmation of the entire Ethereum network, each shard of Ethereum, that is, the chain divided into independent regions, will have its own small ledger, and then communicate through the shard chain In this way, a general ledger is formed, and then the general ledger is packaged by the beacon chain.
Here, the function of the sharding chain is to calculate, store, and output the results, then communicate with the beacon chain, and finally synchronize the ledger of the beacon chain.
Even if Ethereum 2.0 has changed its roadmap now, Ethereum is now also using data sharding, which divides the structure after data generation into independent parts, which is similar to off-chain sharding, except that it does not divide the nodes of the chain. To separate pieces.
This kind of security protection relationship needs to be layered, so many chain designs draw on this idea.
The picture shows Oasis’ layered design ideas
For example, the consensus layer is designed separately, so that the consensus layer is responsible for the security of the entire network, and those calculations are separately processed in the chain outside the consensus layer. For example, in Oasis Network, the consensus layer is designed as Paratime, which is Separate Paratime chains, these chains form their own ledger to the consensus layer, and the security is protected by the consensus layer.
For another example, in addition to the consensus layer of Phala, pRuntime is designed, which is a stand-alone chain node running in the TEE, and it is also a shard of each chain. The security of its data is also protected by the consensus layer confirming the block data.
The cryptocurrency network technology has been very mature, because from the design of the chain over the years, it can be seen that the project party’s understanding of the solution is sufficient to build better infrastructure and applications, but it is worth improving that a chain wants Success is not determined by technology, but by the operation of the chain. The problem of chain operation is still being explored by the project parties and entrepreneurs.
