Rollup will become the king of the Layer 2 world, so where will sidechains go?

Editor's Note: This article comes fromBabbitt Information (ID: bitcoin8btc)Editor's Note: This article comes from

Babbitt Information (ID: bitcoin8btc)Ethereum Roadmap, Author: barryWhiteHat, Compiler: Free and Easy, released with authorization.

Translator's Foreword: With the first wave of impact of decentralized finance (DeFi) applications on the Ethereum mainnet, the call for "expansion" is undoubtedly getting louder, and its attention is even comparable to that of Bitcoin's "block expansion". "In comparison, after the DeFi hype ebbed, the frequency of "Layer 2" keywords began to soar. Vitalik himself even proposed a rollup (Note: the most promising Layer 2 technology) at the beginning of this month.

Ethereum Roadmap

To put it simply, in the short and medium term (in the next 2 years), the expansion of Ethereum and DeFi is mainly based on the rollup layer 2 network. At present, leading DeFi projects such as Uniswap, Curve, and Synthetix have proposed to migrate applications to rollup Layer 2 network plan.

The original author is BarryWhiteHat, a Layer 2 technology researcher.

Introduction

Thanks to Albert Ni for reviewing and discussing this article.

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Introduction

The importance of Layer 2 to Ethereum is growing every week and everyone knows it.

However, "layer 2" is an imprecise label, and nowadays, when people say "layer 2", they often mean "non-Ethereum layer 1". However, the way you interact with Ethereum layer 1 is very important. All the different solutions considered "layer 2" may have completely different properties. Arguably, layer 2 should only refer to something with specific properties (e.g. we might all agree that something that exists on AWS isn't layer 2, but there are items that arguably have similar security guarantees and are therefore considered layer 2). But that might be another topic for discussion.

In this post, I want to delve into the nature of sidechains.

Sidechains play an important role in the Ethereum ecosystem. They have been a scalability and usability stopgap while the research community was still working on better solutions. Products like xDai have highlighted the need for a better user experience that has spilled over into other areas.

• censorship resistance;

• However, sidechains do not have the security properties that the wider Ethereum community expects, but that doesn't mean they should never be used. If people using sidechains are fully aware of the lack of certain properties, and still want to use them, that's within their power. The tradeoff may be worth it, but it can be dangerous when people don't care about it. The purpose of this post is to provide some information, and it wouldn't hurt if everyone knew about the properties, but it would make sense if it would help people recognize false assumptions.

• What security properties do sidechains lack? Almost all sidechains fail to provide:

Guarantees regarding funds;

anti-censorship

I want an open discussion about these properties to benefit everyone.

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It should not be disputed that sidechains are less censorship-resistant than well-designed blockchains, otherwise there would be no need for blockchains. Let's break it down a bit further, though.

If N verifiers are involved in a sidechain, and a transaction can be reviewed as long as M verifiers agree, then NM is the number of collusion verifiers that need to be colluded in order to review a block. This leads to a delicate balance where it is harder to censor transactions, making it easier to censor blocks. Considering that both transaction censorship and block censorship are undesirable, this makes it fundamentally difficult for sidechains to have strong censorship-resistant properties.

This concern extends to using Proof-of-Stake (PoS) consensus mechanisms, which can get worse as the numbers involved are weighted by stake, meaning that the number of distinct entities required to reach a certain threshold may or even lower.

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• Data Availability Guarantee

• We know that NM validators can create a block. We also know that in order to validate a new state, all other validators need to have data about the entire state. So if NM validators are malicious, they can:

Create a new block:

effectively removes N - (NM) = M validators from consensus, thereby controlling the system;

How likely is this to happen? This obviously depends on many details of a particular situation, but we can start by considering the incentives for rational validators to share data with all other validators. For traditional Proof-of-Authority (PoA), not doing so can result in reputational damage. However, side chains based on Proof of Stake (PoS) may have risks. However, this is not easy to do because there is no way to prove that some data is unavailable without someone else putting all the data on-chain. Does this sound a bit like optimistic rollup? Yes, this means that sidechains with better security properties are essentially reduced to optimistic rollup.

In most sidechains, validators receive some form of payment. For honest validators, this reward is shared among N validators. For dishonest verifiers, the same reward is shared between N−(N−M)=M (the most important thing here is that M

state1 => state2 => state3

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finalization

Imagine a series of state transitions as follows:

state1 => state2 => state3

After consensus is reached through the Ethereum main network, the side chain checkpoint block. This might lead one to think that the finality of sidechains is basically equal to the finality of Ethereum. The specific statement is: "In order to restore a block on the sidechain, you need to roll back the block on Ethereum", but this is not the case.

This is because finality is about restoring transactions, not replacing old states with new ones. Thus, NM validators are able to perform the following transitions:

(Replace state3 with state1 so that state2, which is supposedly confirmed, can be restored without needing an Ethereum mainnet rollback)

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Guarantee of ownership of funds on the side chain

Suppose there is a state state1 ={Alice:1000, Bob:0}

So Alice has 1000 and Bob has 0. Now suppose Bob is malicious, and he effectively (or effectively colludes) controls the vast majority of POA validators, what happens?

This is tantamount to stealing all of Alice's funds and giving them to Bob.

Therefore, the defense of the sidechain is reduced to: Assume that N - M validators can never be persuaded to handle this illegal state transition. A lot of people know this, but I think it's useful to remind everyone.

Now, there may be a few people (validators) who can be trusted in this way, just as many of us trust different centralized service providers. Sometimes there are tradeoffs, and it's important to be aware of those tradeoffs.

Problems with governance as a defensive measure

The argument is sometimes made that "we can use governance to solve all the problems mentioned so far."

This is of course flawed as it basically degrades the whole system to governance. One reason this argument worries me in particular is that it implies that other properties of sidechains are bauble (in which case, why should they be?). For example, if governance is the last resort to prevent the above problems, then this means that Proof of Stake (PoS), Proof of Authority (PoA), etc. do not really matter.

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• If you specifically want N−M validators to be able to perform arbitrary state transitions. An example would be an enterprise application that wants to have a master control switch;

final thoughts

When M = 0, and you want N validators to be able to perform arbitrary state transitions (e.g., in a four-party game). One problem here though is that 1 validator can unilaterally stop the blockchain;

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• final thoughts"In the past, sidechains were the only viable solution for certain use cases that wanted to maintain compatibility and interoperability with Ethereum. And now, as other layer 2 scaling solutions mature, it is a good time to consider how to make sidechains more compatible with these solutions."；

• Enables mass migration at no cost to ensure users can exit without being locked out due to costhere）；

• stuck

• Replace the leader election mechanism with a stronger anti-censorship function (PoS seems to be a wrong direction, see

here