Host: Jomosis, Geek web3

Guests: Kevin He, Co-Founder of Bitlayer;

Baiyu, CKB Eco Fund Partner;

Kai, Researcher of Bool Network

On the evening of May 16, Geek web3 invited guests from Bitlayer, CKB, and Bool Network to discuss various issues related to Bitcoin Layer 2 on Twitter Space. Many interesting topics were covered, and due to the extensive discussion, the written record has been divided into two parts. The second part of the discussion includes:

Compared to Ethereum, Bitcoin is not suitable as a base layer for Layer 2. What are the obstacles it poses to Layer 2?

Recently, the xlink cross-chain bridge was hacked for over $4 million due to a key leak. The security of cross-chain bridges, especially withdrawal bridges, is one of the core issues of Layer 2. How does your team address the security issues of withdrawal bridges?

The Lightning Network and RGB protocol were once highly anticipated, but their ecosystem development has been disappointing. What are your views on this?

In the current Bitcoin Layer 2 ecosystem, which projects are superior in terms of technology or overall narrative? Why?

What issues need to be resolved for Bitcoin Layer 2 to achieve the popularity of Ethereum Layer 2?

During the discussion, the guests frequently made insightful remarks. Baiyu candidly stated: "I think the biggest obstacle for the Bitcoin ecosystem is that Ethereum has been too successful, leaving many with a deeply ingrained Ethereum mindset."

Due to the extensive content, we have divided it into two parts. Below, we welcome you to read the second part and draw inspiration from the guests' brilliant speeches.

1. Jomosis: Bitcoin is actually not suitable as a base layer for Layer 2. What are the obstacles it poses to Layer 2?

Kevin: The main obstacle is the implementation of Layer 2 technology. Personally, I believe the key to Layer 2 is whether large holders, especially whales, recognize and feel secure with it. However, from what I understand, many large holders or whales are still reluctant to move BTC to Layer 2 or enter such unreliable yield channels, and they often distrust CEX.

We can see projects like Babylon with a clear security model that can solve some issues, gradually gaining recognition from Bitcoin holders and even institutional investors. This allows more people to see that Bitcoin can move to Layer 2 or another area securely, locking it on the original chain and earning yields elsewhere, gradually gaining acceptance in user perception.

Returning to our initial question, from a technical standpoint, the core issue is Bitcoin's limitations. Specifically, Bitcoin lacks verification capabilities on-chain. When it lacks verification capabilities, it becomes difficult to verify a withdrawal action on Layer 2 when moving back to Layer 1, making secure bi-directional cross-chain bridges hard to implement.

Additionally, under the UTXO model, each UTXO is an independent parallel space, making it difficult to create interrelated scenarios. Features like Covenants have not yet gained community acceptance.

Another point is that Bitcoin lacks a global state. Without a global state, many functions like escape hatches and forced withdrawals, or scenarios based on certain verification results, cannot be implemented. They can only be achieved through off-chain indexers, light nodes reading transactions, or specific transaction methods for reverse indexing or linking.

In summary, the understanding of Bitcoin and Layer 2 needs to advance, and technical breakthroughs are needed. For example, CKB has innovations like the Cell model, and BitVM attempts to implement verification on Bitcoin, making the Bitcoin ecosystem very different and better than before.

Baiyu: I think the biggest obstacle is that Ethereum has been too successful, leaving many with a deeply ingrained Ethereum mindset. Ethereum was very avant-garde back then, breaking through the Bitcoin fundamentalist community and showing that blockchain could be used as a smart contract platform, abandoning the UTXO model for an account model.

Although Ethereum seemed avant-garde back then, over the years, it has become clear that Ethereum is best suited for financial applications. Even its founder admits it is a highly financialized world, with ENS being the only large-scale non-financial application, which was ironically boosted by a comment from Vitalik Buterin.

Currently, when we build in the Bitcoin ecosystem, we habitually bring over things from Ethereum. People are building in the Bitcoin ecosystem, not knowing when they might be swayed by a comment from the existing Ethereum forces. Recently, I met a friend who I wanted to join the CKB North America team, but he had been in the Ethereum community for a long time. After hearing my ideas, he asked, "Why do this in the Bitcoin ecosystem when it's already on Ethereum?"

Many elites share his view, thinking that what is being done in the Bitcoin ecosystem is already available on Ethereum, so why bother with Bitcoin? Why start over? I am tired of hearing such questions, so I believe the most important thing this time is to think about how to use the Bitcoin ecosystem to do things that the Ethereum ecosystem cannot. Ethereum keeps changing, ultimately focusing on Staking and Restaking. Should we do the same in the Bitcoin ecosystem?

I think breaking free from the Ethereum mindset is key and the biggest obstacle to attracting top talent to the Bitcoin ecosystem. How can we attract the best minds to build in the Bitcoin ecosystem and push blockchain forward?

2. Jomosis: Recently, the xlink cross-chain bridge was hacked for over $4 million due to a key leak. The security of cross-chain bridges, especially withdrawal bridges, is one of the core issues of Layer 2. Many Layer 2 solutions still use simple multi-signature bridges, which are prone to internal collusion or external attacks. Could the guests introduce how their teams address the security issues of withdrawal bridges?

Kai: To put it simply, the problem with Bitcoin cross-chain bridges is that, due to Bitcoin's non-Turing complete script, it is impossible to perform certain verification calculations on the Bitcoin chain using Ethereum's mechanisms. Based on this issue, we at Bool Network have thought of many solutions. The simplest way is to treat each Layer 2 as a centralized CEX, where a decentralized asset custodian manages cross-chain transactions.

Bool Network continues this approach by making asset custodians more decentralized. To achieve this, the first step is to solve the security issue of cross-chain bridge witnesses, which can be achieved through permissionless access using POS. Then, we use TEE and MPC along with our proposed RingVRF to dynamically select cross-chain bridge witnesses from the Bool network. Simply put, out of 200 nodes, a few are randomly selected by an algorithm to act as cross-chain bridge witnesses.

TEE ensures that all code logic runs according to specified constraints, making it difficult for external parties to breach the code running in TEE or maliciously modify the data. Based on this, our MPC solution can continuously switch the cross-chain bridge key custodians among hundreds of nodes within the Bool network.

However, Bool network nodes are public, so we also need to address privacy issues to prevent attackers from deducing who the cross-chain bridge key custodians are. We propose RingVRF with privacy protection features. Simply put, you can prove that your public key is part of a set of N public keys (the set itself is hidden through cryptographic methods), and then you prove that you belong to

When a member of the set is realized through ZK, you can prove your identity without revealing which public key is yours, only needing to broadcast a temporary communication public key.

So our overall logic is very clear: We hide the DHC (Dynamic Hidden Committee) nodes of the cross-chain bridge within the entire witness network, which may have hundreds or thousands of nodes. Then, we use ZK+RingVRF to hide the identity (public key) of each witness node within the DHC, so that the outside world does not know who the witnesses of the cross-chain bridge are. Additionally, since each node must run TEE, the private key shards of MPC and core programs, and all computational processes are hidden within the TEE environment, no one knows the specific computational content. Even the selected cross-chain bridge witnesses do not know they have been selected, fundamentally preventing collusion or external breaches.

Baiyu: For CKB, we categorize assets into two types: one is Bitcoin itself, and the other is derivative assets issued on Bitcoin, such as BRC-20 or various runes. We have internally researched that if Bitcoin does not undergo a hard fork or soft fork, the most ideal bridge/second-layer solution for verification capability is BitVM, but BitVM still requires a long time to be implemented. Therefore, it can be considered that in the short term, there is no cryptographically secure way to safely move Bitcoin back and forth between the first and second layers.

In this situation, we believe that Bitcoin cross-chain bridges are prone to two extremes: either extreme centralization, such as financial institutions with licensed custodians, where large holders feel secure because of legal oversight. The representative of this type of solution is actually WBTC, which has a market value of tens of billions on Ethereum, right? It is done by the company BitGo.

The other extreme cross-chain bridge solution is as decentralized as possible. But the differences between bridges are very significant; not all bridges are the same. The differences between bridges can be even greater than the differences between bridges and non-bridges. It is crucial to understand the trust level of the bridge. The ultimate goal is to achieve something similar to the POS model, relying on economic security measures to approach cryptographic-level security, where witnesses can be punished if they act maliciously.

However, various models of Bitcoin cross-chain bridges have been experimented with on various BTC-ETH cross-chain bridges, and many methods have been thought of long ago to move Bitcoin to the Ethereum chain. There is no need for us to think of other things. Among the more decentralized solutions, I have seen TBTC, but TBTC may not be very user-friendly and is not widely used.

We at CKB are also talking with Bool Network to see how to cooperate. We are also working on solutions similar to WBTC. Another one is similar to RGB++ or other UTXO-type asset protocols, which can achieve trustless transfers between CKB and other UTXO public chains through homomorphic binding.

As for whether homomorphic binding can be combined with DLC or some progress on the BitVM side to allow it to be verified on BTC, and then we use RGB++ to issue an RBTC, similar to Wrapped BTC, we are considering this type of solution, which seems to have some hope, but we cannot draw a conclusion yet.

So everyone should be aware that a bridge is like a honeypot, with so much money locked inside, and there is also a risk that, besides hacker attacks, the team might suddenly encounter irresistible external forces, like Multichain, and the money could be lost.

Kevin: Let me briefly talk about the issue of bridges. First, there is no absolute correlation between security and decentralization, like FireBlocks, which also manages a lot of funds, but we haven't seen them lose a lot of money. On the contrary, those decentralized bridges lose money every day, so currently, there is no absolute correlation between security and decentralization.

Second, we still need to find more advanced bridges, which requires us or the community to create innovative things to make a bridge trustless, because Trustless itself will benefit the custodian of the bridge, making it safer, which is what we need to pursue.

Then let's look at the model of the bridge. Traditional bridges basically have users entrust their funds to the bridge operator for safekeeping, and users completely lose control over their assets. The direction of the funds is controlled either through multi-signature, POS, fraud proofs, or ZK verification to prove the validity of cross-chain messages. This type of model has a problem: users completely lose control over their assets, so is there a way for users to retain some control?

During our research at Bitlayer, we found that the DLC model might bring some new changes. In the DLC model, when users and the platform lock assets, it is done through 2-2 multi-signature and pre-signature methods, predicting future outcomes, so users do not completely lose control, and if it is an OP-DLC bridge, the worst-case scenario is encountering a non-cooperative cross-chain bridge, but it won't result in asset misappropriation. Ultimately, we found that bridge solutions based on DLC or channels can bring new changes in trust models or power distribution schemes.

So in our technical white paper and the second phase of the testnet, there will be some involvement in this area, hoping to provide the market or community with a new choice.

Let's talk about the issue of key leakage. Most of the major theft incidents in the past were due to key leakage, either through social engineering or other reasons. So how should we manage keys? The MPC solution can solve part of the problem, and then there are principles like cold-hot separation and multi-signature role separation, which are actually industry standards. We will provide our developer community with something similar to a Security Codebook.

3. Jomosis: The next question is about the Lightning Network and the RGB protocol. Both projects were highly anticipated in the past, but their ecosystem development has been disappointing. What are the guests' views on this?

Baiyu: Our favorite route for Bitcoin is the Lightning Network. As Cipher and Jan said, the Lightning Network is the beacon of the Bitcoin world, and we very much hope to promote things related to the Lightning Network. However, the Lightning Network has been building in the Bitcoin ecosystem for five or six years, right? A big company like Lightning Labs is pushing it, but the progress has been very slow. I think this is a problem exhibited by the Bitcoin community, so more teams like CKB need to emerge.

We see that CKB proposed to build its own Lightning Network, and then RGB++ can be reused in the Lightning Network, and the development actions of Lightning Labs have also accelerated. We believe that the Lightning Network should become more open, rather than concentrating the right to speak in the hands of a few centralized companies, but becoming an open standard, which can be compatible with any standard-compliant UTXO asset on the Bitcoin layer. But Lightning Labs is now more focused on doing Taproot Assets themselves, and the Lightning Network infrastructure will first be compatible with Taproot Assets, not becoming completely open.

We hope that the Bitcoin ecosystem can continue to promote the openness of technical standards such as the Lightning Network. In our view, it is currently more ToB rather than directly ToC. Many users cannot tolerate the operational experience of the Lightning Network, and the latter sacrifices UX convenience for security. To achieve convenience, some security must be ceded. Many service providers similar to financial institutions survive in the Lightning Network ecosystem. We can see that these institutions have made some compromises on security, but their products are very convenient, such as LSD, which also considers compliance in the solution design. This is what I know about the progress of the Lightning Network.

Then CKB's own Lightning Network will be on the testnet around mid-June, and some tests will begin. We look forward to everyone testing some of our things. We hope that the Lightning Network, combined with RGB++, and a PassKey wallet like Joyid, can truly be used on a large scale.

Regarding the second topic, RGB, I think when we discuss it, it is better to directly discuss the two things it includes. One is CSV, which is client-side validation, a very important scaling idea in the Bitcoin community. Unfortunately, CSV has been buried and not much discussed. More people still want to use Ethereum's approach to scale Bitcoin, but when scaling Bitcoin, it is not about creating another chain outside the Bitcoin chain, but about creating a P2P network outside the chain.

The core of the Bitcoin community, in my opinion, is P2P, which is peer-to-peer connection, allowing us to directly verify important things with each other. CSV is basically this idea, which is to build a P2P network outside the Bitcoin chain, where everyone can spontaneously verify the validity of transactions between two people. To achieve this, there is another core concept, which is single-use seals, using UTXOs on the Bitcoin chain as Single-Use Seals.

The above two points are the core of the RGB protocol.

心的两点，可以做很多很多文章，CSV你可以把它看作一个服务，然后你可以做一个DAPP形态的CSV平台，CSV可以用as a service的形式去做。当然CKB基于RGB做的最核心的事，就是做了RGB ++，我们把CKB当做RGB在链外的一个客户端，通过同构绑定就可以保证安全。

其实还有一个比较大胆的想法，就是基于比特币做CSV可能不是最好的选择，因为比特币的验证能力有限，但你可以在CKB上去做CSV，包括在CKB上结合Nostra去做一些事情。我们这几天可能就会发布一个技术方案，就是说 Nostra怎么结合CKB，然后鼓励很多项目方来做一些社交相关的东西。

总而言之，我总结一下，大概就是比特币社区有RGB的思路，有闪电网络的思路，这些都是比特币社区非常优秀的协议，应该被发扬光大，结合这些东西就可以做出我前面提到的以太坊上做不到的东西。以太坊当年是想做闪电网络的，如果是进圈早的人，应该知道以太坊有一个东西叫雷电网络，后来做着做着就不做了，完全放弃掉了，但这是比特币能做的事情，那我们为什么不沿着这个方向继续往下走呢？

而且据我所知，以太坊那边也有一些项目在做CSV客户端验证的事情，但这些东西其实都来自于比特币社区，所以我们是可以把它发扬光大的。

Kevin：关于闪电网络，没记错的话，最早是想要做小额支付，但这里有个根上的问题，就是用比特币来做小额支付不如用稳定币做，闪电网络本身支持的资产类型比较匮乏是个问题。像Ordinals还有BRC-20、Runes这种协议的被认可，结合这种新的资产发资产协议来推出稳定币，然后在闪电网络里面进行支付或者交换，这个事情是不是可能有新的发展？我也是非常期待。

我们在启动Bitlayer之前其实调研过RGB，但我们没有采用这样的技术路线，觉得这种小众的协议还需要一些市场的教育。对于我们来讲，会更加考虑市场多一些，会更加考虑被广泛被接受的东西，所以我们最终尝试在比特币上去做BitVM，并且以现在的BitVM社区规模，新的技术突破真的有希望实现，在不需要多少的BTC主网软硬分叉的情况下都可以做，而且我们关于BitVM的POC已经跑通了。

总体来讲的话，我们这边的思路是期望整个比特币生态百花齐放，让更多的观念得到大家的认可。Bitlayer其实也有多个VM或者多个安全模型的支持能力，在验证能力方面有了突破后，我们也可以支持不同的编程模型。

Kai：闪电网络更多还是受限于它的非图灵完备，没有智能合约，没办法去很好的拓展应用，因为闪电网络最初定位也只是小额的快速支付。对于CKB来说，它是对闪电网络的一个很大改进，可以实现图灵完备。

Baiyu：我觉得刚才Kevin老师和Kai都讲到了很重要的两点，其实当今的闪电网络已经不是单纯用来小额支付的了，现在没有人会用比特币去做支付了，大家还是把它用作资产存储，而且散户手里没有多少比特币，真正可能的场景是，我觉得闪电网络会成为一个基础设施，会去兼容在比特币上发行的各种资产协议。

比如说你用RGB++去发行USDT，然后这个USDT可以进到闪电网络，所以闪电网络更像一个高速路，你可以让其他的车子也进去，原来里面只有一种车就是比特币，现在可以让其他车也进去，这是它最大的一个变化。

第二点我觉得比较重要的是，刚才Kai老师说的，比特币的闪电网络还是非图灵完备的，但是在CKB上闪电网络可以去加一些条件，起码可以让闪电网络里兼容多种资产协议，然后你就可以完成swap，甚至你可以在闪电网络里面做defi，这里面想象空间很大。

4.Jomosis：比特币二层想要达到以太坊二层的体量，还有多少问题要解决？

Kevin：第一个是认知问题，大家需要认可比特币除了价值存储以外的特性，第二个就是技术问题，还要去解决链上验证的问题，还有就是客户端验证的这个思路，要被大家广泛接受。

Baiyu：我觉得大家其实放低了对比特币生态的预期，以太坊生态发展了很多年，然后探索出来了适合其技术架构的应用，但比特币生态还需要更长的时间来构建出繁荣的生态，所以会站在以太坊的肩膀上，在生态建设上会对其有一些借鉴，我觉得这是重要的一点。

当然，我们还要围绕着比特币原有的一些东西去探索，比如说UTXO到底可以做什么？比如说我们在探索UTXO是否更适合去做NFT相关的东西，因为它本来就是并行化的，而且是用户个人拥有的，不是被智能合约所拥有的资产。

然后在Defi赛道里看UTXO，其计算流程是在比特币链下做计算，在链下做完了计算后把结果放到链上去验证，链下计算—链上验证这样的技术架构，更适合做intent和OrderBook，做Orderbook型交易平台最早就是以太坊的想法，但他们的order book做得不理想，最后出来的是AMM自动化做市商，但在比特币生态这边未必是这样。这些都需要更长的时间去摸索，然后需要走向市场。

Kai：比特币二层要保证它的去信任和安全性的，给出一套标准化的Layer2解决方案，同时这个Layer2的体验要好，比如很多二层支持的账户体系，还是以太坊的账户体系，但你也可以直接沿用比特币的那套账户，到二层上面去开辟场景。当然这些只是设想，我感觉最后的话肯定会有更好的方案出现，来解决现有的一些问题。

5.Jomosis：在当前的比特币二层生态中，哪些项目方在技术或者是综合叙事上，是你们比较欣赏的？

Kevin：这个问题肯定要说Bitlayer了，哈哈。我觉得Bitlayer有比较清晰的架构，还有解决问题的思路，我们找准了待解决的问题，也找到了解决问题的好方法，同时我们这边也针对既有方案做了一些创新，例如说，我们可以在不依赖OP_CAT操作码的情况下，基于Taproot在BTC链上做FRI或对STARK进行验证（基于BitVM），这其实也是我们的创新。

之前提到的OP-DLC桥，也是我们寻找到的更好的资金控制模型，还有这个多VM的设计，我们都还是花了比较多的思考和精力的。总的来讲就是，我们希望说能推动BitVM相关的技术社区往前走一步，比如说我们帮助BitVM中文社区和极客web3联合落地了BTCEden这个比特币二层风险评测网站，期望也是能提供一些public goods给社区。

同时我们也帮助了BitVM社区建立社群，BitVM的中文社区现在应该有大几万的follow，我们做了大量的科普，坚持的去做BitVM的周报，相当于是把我们内部的研究内容外化为一个产品的形式，期望说能将更多的人吸引到BitVM 的研究和开发过程中，这对于所有的开发者都有益处。

然后我们其实也很高兴的看到，BitVM这个大家庭在快速壮大，至少超过6、7个项目都是要围绕着BitVM进行构建，我们也是BitVM的一个核心贡献者，我们的研究员刚赢得了关于SHA256 OPCode的挑战赛，获得了奖金。我们也期望是有更多的项目方一起加入进来，在这方面进行探索和突破，使得比特币上真的能不需要太多软硬分叉也能实现验证能力，这将会造福整个比特币生态。

同时像今天在坐的CKB团队，还有Bool，我觉得也是非常有特色的团队，有自己的坚持，有自己的特色，也有很好的落地，这个也非常值得尊重。

Baiyu：我最欣赏的当然就是RGB和RGB++代表的CSV路线，和闪电网络这样一个快速支付的路线，这两个路线有一个特点都是在链外扩容，然后在一定程度上依赖比特币UTXO的安全性以及比特币脚本很有限的能力，这是比特币生态里很独特的东西。

我们总是想把比特币改的像以太坊一样，比如智能合约的验证能力，然后可以做很多很多的事情。大家会一直在链下探索怎么搞更多的东西。然后我也是希望更多的团队可以探索出创新之路，我们总是羡慕一个Uniswap出来了， 500行代码就可以写出一个Uniswap，但其实在Uniswap之前也，有其他的Defi协议，还有更多的人做了很多尝试，最后才有Uniswap跑出来。

我觉得现在比特币生态也处在这样一个前夕，就是有大量的创新想

Law, various ideas, but they have not been fully realized by everyone or turned into products and brought to market. In fact, many such opportunities can be found, this is my opinion.

Kai: I think the BitVM bridge is a very good solution, but it will take a long time to implement. In the meantime, some alternative solutions may be needed, such as multi-signature or MPC solutions to address some of the current issues with Bitcoin's second layer. Therefore, our Bool Network can help Bitcoin ecosystem projects in the early stages to quickly build some applications from Bitcoin to the second layer.