Author: Master of Five Fireballs

Original Title: "The Multi-Chain Era Erupts: A Comprehensive Look at Those 'Promising' New Solutions from Five Perspectives"

"To get rich, first build the road."

I believe that as long as you are not too young, you should be very familiar with this slogan. What does it have to do with blockchain? Because we are also starting to "build roads," but here we call it "bridges."

Originally, there was only one Ethereum in the world, like a big village where all production and consumption activities took place—blacksmith shops, farms, money houses, markets… Everyone was very close to each other, and there was no issue of "building roads."

Now, the blockchain has officially entered the multi-chain era, with many other villages opening up next to Ethereum Village. Although none of them are as large as Ethereum Village, they all have their own blacksmith shops, farms, money houses, and markets…

Gradually, many villagers who found Ethereum Village too crowded and expensive "immigrated" to other villages, and over time, the populations of several villages increased, marking the end of Ethereum Village's dominance.

Then, the matter of building roads was officially put on the agenda, as there needed to be economic and information exchanges between the villages, and many villagers needed to transfer funds between them.

So the question arises: how should this road (bridge) be built? Smart people have thought of the following methods:

Find a Bank

Originally, Ethereum Village had a few large money houses, such as Bian'an and Shui Bi. As the surrounding villages gradually became prosperous, these money houses opened branches in other villages. Since these money houses had a good reputation, the villagers trusted them.

When they needed to transfer funds or send money to other villages, they often turned to these money houses, which provided deposit and transfer services for various villages. This was the earliest commonly used CEX solution.

Strictly speaking, this cannot be considered a "bridge," but it is indeed a simple and effective solution, or rather, the only solution before the bridge era.

However, having only money houses is not enough, as they could also go bankrupt. More importantly, in a blockchain environment that emphasizes "decentralization," relying on "centralized" money houses for such important business is quite embarrassing…

Thus, other solutions emerged.

Single Point External Verification

A simple understanding of cross-chain bridge solutions: single point external verification, multi-point external verification, and native verification, etc.

Setting aside the drawbacks of centralized money houses, in many scenarios, money houses cannot meet people's demands at all.

For example, the Bitcoin held by villagers in Bitcoin Village is recognized by every village, but this Bitcoin cannot be taken out of Bitcoin Village. What should people do if they want to use Bitcoin in Ethereum Village or other villages?

Someone found a respected elder who did not belong to any village and discussed this matter with him: if villagers from Bitcoin Village deposit a certain amount of Bitcoin with the elder, he would issue them a receipt that could circulate freely in Ethereum Village, representing the same value as the Bitcoin deposited with him.

At the same time, the Bitcoin deposited with the elder would also be "locked" with him and could not circulate until someone presented the receipt to "unlock" the Bitcoin.

The benefit of this approach is convenience. When people from Bitcoin Village want to use their Bitcoin in Ethereum Village, they only need to find the elder to deposit their money and receive the receipt, which works just like Bitcoin in Ethereum Village.

The downside is that this respected elder, although reputable, might succumb to the temptation of easy money and run away with everyone's deposited Bitcoin.

The Bitcoin receipts circulating in Ethereum Village would become worthless without the backing of the deposited Bitcoin assets, causing significant losses to users. It is not hard to see that this represents the "single point external verification" bridge exemplified by WBTC.

All security depends on the reputation of the institution that holds the BTC and issues WBTC.

Multi-Point External Verification

Since we are not too confident in that "respected elder," how about finding several reputable elders to handle the deposit, locking, and issuing of receipts together?

Each of them may not have the same reputation and virtue as the previous "respected elder," but there are more of them! Moreover, they usually have to pledge a large amount of assets to qualify as "validators."

Under the conditions of asset pledging and gaming, the likelihood of them collectively "acting foolishly" is significantly reduced, making them overall more reliable than a single elder.

This is why we talk about "decentralization." Representatives of multi-point external verification include the recently popular Anyswap, Synapse, and the previously well-known Rune.

Native Verification

A simple understanding of cross-chain bridge solutions: single point external verification, multi-point external verification, and native verification, etc.

It sounds impressive, but what is native verification? Everyone knows that the order of each village is maintained by the police (miners) in the village.

Villages with a long history, such as Bitcoin Village and Ethereum Village, have always had very good public safety, and people have a high level of trust in the police. Newer villages, although they have not yet accumulated enough reputation, such as Near Village and Cosmos Village, also have good reputations and orderly public safety.

What if we conduct asset transfers between two reputable villages under the collective witness and guarantee of the police (miners) from both sides? Wouldn't we no longer need to find one or more elders from the outside world?

Even better, under the witness of the police from both sides, people from both villages can not only transfer assets but also exchange messages! This truly achieves "shouting across the void." Clearly, the security and reliability of the native verification model do not require external individuals or asset pledging…

However, the downside is also obvious: it requires the participation of the police from both villages each time (developers need to deploy new lightweight client smart contracts on both the source and target chains for this native verification bridge), so it lacks flexibility compared to external verification models.

Bridges of this style are naturally represented by the well-known Cosmos IBC and Near's Rainbow Bridge. Multi-coin and Layer Zero, which was recently invested in by Binance Lab, are also noteworthy newcomers.

Local Verification (Liquidity Network)

This model is basically an extension based on the Bitcoin Lightning Network model. To understand the typical model of this bridge, one must first understand two terms: atomic swaps and hash time locks.

What does this mean? For example, if a person wants to transfer their Ethereum from Village A to Village B, is there a method more reliable than an elder or even the police from both villages?

Indeed, there is: a robot without emotions or moral flaws! The atomic swap based on hash locking is such a robot. The robot receives a payment with a hash lock from your address in Village A and specifies an expiration time lock, then sends a transfer with the same hash lock to your address in Village B.

After you discover this transfer at your address in Village B, you publish the key in Village A to unlock the hash lock and release the funds to the robot. Then the robot uses the same key in Village B to unlock the hash lock and give the funds to you. If you do not publish the key, both parties can return their funds through the contract after the time lock expires.

In this case, you do not need to rely on the robot's reputation or moral standards, but rather on cryptography to achieve Code is Law, known as "routers." The liquidity-providing relay nodes and contracts form the "robot" mentioned above.

The representative of this type of bridge is undoubtedly the recently popular Celer, while Hop and Connext, which have not issued tokens, differ slightly in technical implementation from Celer but overall also belong to the local verification liquidity network bridge model.

Summary

Currently, mainstream bridges can be categorized into these five major types. However, the world of blockchain is changing rapidly, and the multi-chain era has officially arrived. As various public chains continue to develop technologically, the underlying technologies, economic incentives, and game models of bridges will also continue to evolve.

Different scenarios and needs will certainly require different types of bridges to meet them. Let us look forward to the "hundred flowers blooming" of public chains and the fierce "battle of a hundred bridges"!