Exclusive Interview with Zulu Network CTO: "Creating a True L2 Scaling Layer in the Bitcoin Network"

Author: Wenser, Odaily Planet Daily

As competition in Ethereum's L2 networks reaches a fever pitch and the Bitcoin network ecosystem becomes increasingly rich, Bitcoin's L2 networks are becoming the "next crypto stronghold." As a "new star" in the Bitcoin L2 network that adopts a dual-layer architecture and has recently successfully developed ZKP verification, Zulu Network is expected to be the first to connect the Bitcoin L1 network, Bitcoin L2 network, and L3 network.

Odaily recently conducted an in-depth interview with Zulu Network CTO Cyimon, sharing the behind-the-scenes dynamics of the Bitcoin L2 network.

Q: Could you please introduce yourself briefly, including your past work experience and the responsibilities you have taken on since joining the Zulu Network (hereinafter referred to as Zulu) team?

Cyimon: I entered the blockchain industry in 2018, mainly focusing on the ZK field, and I have about six years of technical experience now. I joined the Zulu team in October last year. The reason I chose the Bitcoin L2 track is mainly due to the release of the BitVM white paper. Based on these theories, we can truly realize the vision of Bitcoin L2. After joining the Zulu team, I have been handling the coordination of technical directions and development-related work, which we will detail later, including Zulu's unique design and current technical progress, etc. Overall, we at Zulu aim to bring more expansion capabilities to the Bitcoin ecosystem.

It is worth mentioning that as the industry's first Bitcoin L2 project to simulate ZKP implementation using Bitcoin Script, Zulu has also made significant contributions to the official BitVM 2 GitHub repository, earning high praise from BitVM inventor Robin Louis.

Tweet released by Robin

Q: What challenges does building an L2 on the Bitcoin network face? What technical solutions are being adopted by other Bitcoin L2 networks on the market?

Cyimon: I think this question is crucial as it directly reflects the core vision behind Zulu's establishment. As a Bitcoin L2 network, or rather before the Bitcoin L2 network became popular, most people had only heard of Ethereum's L2 networks. The main issue faced by both Bitcoin L2 and Ethereum L2 is: how does an L2 network, as an off-chain network of a public chain, inherit the security of the L1 network?

For Ethereum, this is a relatively straightforward task because it is already very mature; for example, it can verify ZKP and has a certain level of programmability. However, when placed on the Bitcoin network, this becomes a rather awkward situation because the limitations of ZKP's programmability directly lead to the inability to verify the on-chain state of the L2 network on the Bitcoin network. This limitation has resulted in many Bitcoin L2 networks on the market having on-chain states that are not directly related to the Bitcoin network itself. In other words, their on-chain states may claim to generate a ZK proof, but this proof has never been verified on the Bitcoin network. So, from a certain perspective, these Bitcoin L2 networks resemble sidechains. Therefore, I believe a key challenge in building an L2 network on the Bitcoin network is how to allow the L2 network to enjoy the security of the Bitcoin network without forking the Bitcoin network itself.

The security here mainly involves two aspects: the first aspect is the economic security of the Bitcoin network, which can form a POS network through staking to maintain the verification of off-chain states. If issues arise, corresponding assets will be penalized; the second aspect is the network security of the Bitcoin network itself, which is POW network security. In this state, ZKP verification is not conducted through a staking node network but rather by placing it on the Bitcoin network. This is what we truly want to achieve, and it is a key issue that a Bitcoin L2 network must solve: how to inherit the security features of the Bitcoin network? Therefore, the on-chain security of other Bitcoin L2 networks is actually not closely related to the Bitcoin network, and a challenging question here is how to complete ZKP verification on Bitcoin?

Zulu has actually been focusing on how to achieve programmability and implement ZKP on the Bitcoin network since the release of the BitVM white paper. After several months of effort, we finally announced a phased achievement last week, which is that we can currently implement ZKP verification using Bitcoin scripts * (Note: For details, see * Zulu Open-Sourced ZKP Verification Code Using Bitcoin Script, Involving Mainstream Algorithms Groth 16/FFlonk*). This is a significant technological breakthrough in the industry, representing that once zk verification can be implemented through Bitcoin scripts, it can punish malicious parties through a challenge mechanism similar to Arbitrum. Therefore, this indirectly allows us to enjoy the security of the Bitcoin network. Compared to other Bitcoin L2 networks, this is Zulu's unique technological implementation method and a leading solution approach.

Q: In terms of design thinking and philosophy, how should the dual-layer architecture mentioned multiple times in the official documentation be understood? For example, its characteristics, functions, competitive advantages, etc.

Cyimon: To discuss this, we need to start from the design philosophy behind Zulu, making it easier for those who are not very familiar with technology to understand the dual-layer architecture intuitively and clearly.

To discuss this, we must first clarify: why does the crypto industry need L2 networks, or why does Bitcoin need L2 networks more?

As mentioned in the first question, where does the security guarantee of the Bitcoin L2 network come from? The reason Zulu adopts a dual-layer architecture is primarily due to functional considerations. Taking Ethereum as an example, because it has programmability, Ethereum's L2 networks mainly help the L1 network solve two problems: one is TPS, and the other is operating costs. However, for the Bitcoin network, in addition to cost and TPS issues, we also want an L2 network to provide expansion support and realize functions that the existing Bitcoin network has not yet achieved, which is the reason for the dual-layer architecture design. Returning to Ethereum, during its early design phase, the Ethereum network was not a ZK-friendly native environment, and the emergence of L2 networks or the development route centered around Rollup provided an experimental ground for more innovative designs. This means that some innovative functions or technologies can be tried on the L2 network in a limited scope, and if the technological superiority is validated and recognized on a larger scale, it can then be fed back to the L1 network. This is also the reason why Ethereum gradually integrates Rollup and ZKEVM into the L1 network.

So, returning to the Bitcoin network, while helping the Bitcoin network expand TPS and reduce operating costs, functional expansion is also an important aspect.

This brings us to the other layer in our dual-layer architecture—the L3 network, which can be simply understood as a "functional expansion layer." This layer aims to increase programmability while maintaining the original UTXO asset types of the Bitcoin network, laying a foundation for more entrepreneurs to engage in research and development work in the future.

The currently launched L2 network primarily targets DeFi specific to the Bitcoin network, or what we in the industry generally refer to as BitcoinFi. Since the Bitcoin network and Bitcoin itself are high-value assets, if we want to activate these assets, we generally prefer to use a more mature DeFi framework. Zulu's L3 is an expansion platform based on UTXO programmability, often employing a newer programming language and a brand-new virtual machine. If we were to build DeFi applications right away, there could be potential security risks. Therefore, before that, to facilitate the rapid utilization of existing Bitcoin assets in relatively mature DeFi applications, a Bitcoin L2 compatible with EVM has become the best solution, which is to release existing liquidity through more secure applications. The L3 network is designed to lay the groundwork for more future development and innovation. This is Zulu's significant competitive advantage.

Currently, most Bitcoin L2 networks are EVM-compatible or only EVM-compatible, allowing users' Bitcoin assets to flow into DeFi applications. However, this offers relatively little innovation or increment for industry users and the Bitcoin network, as the gameplay is not much different from Ethereum. Therefore, Zulu's dual-layer architecture has more room for development compared to other Bitcoin L2 networks.

Finally, let me emphasize our security. As mentioned earlier, our security implementation mainly reflects that the L3 network will be terminated in the L2 network, and the state of the L2 network will enjoy the network security of the Bitcoin network itself through ZKP verification. This is also our latest development achievement. From this perspective, Zulu is the only Bitcoin L2 network that can enjoy the security of the Bitcoin network.

Q: I have also learned about the development progress of Zulu bridge and Lwaiz V4. Could you elaborate on this?

Cyimon: Lwazi V4 is the code name for the testnet version. The Zulu bridge is a unique bridging tool currently under development, which can achieve off-chain state verification on the Bitcoin network through ZKP. This is a core value of Zulu. If we get specific about user participation, we will later release a trust-minimized Bitcoin bridge, allowing users to participate in cross-chain and bridging of Bitcoin network assets. At the same time, user participation will help us test the security and convenience of the Zulu bridge. For details, please pay attention to the subsequent release of official documentation.

Zulu Network Three-Layer Design Architecture

Q: From a final perspective, what application scenarios does the Bitcoin network need to support, what necessary components are required in the ecological architecture? Will the Bitcoin network generate multiple L2 networks like the Ethereum network?

Cyimon: The application scenarios of the Bitcoin network are worth answering first.

Currently, we can see that besides Bitcoin, there is actually no second asset on the Bitcoin network, which is quite an exaggerated situation. Previous inscriptions and the recently popular rune project have not broken through the asset framework of Bitcoin. Therefore, I believe the Bitcoin network and Bitcoin itself contain immense potential. Specifically regarding application scenarios, firstly, there are projects like Babylon that aim to activate existing assets through staking or other actions to truly release the liquidity potential of these assets. This is one aspect. Whether it is possible to enhance network security while activating existing assets is also a very promising application scenario. This is also why some projects choose the asset staking or re-staking track on the Bitcoin network, as these trending projects are based on the massive funds of the Bitcoin network, aiming to realize the appreciation of Bitcoin network assets.

Given that the Bitcoin network currently lacks other high-market-value projects, another important scenario is to support programmability based on Bitcoin asset types, thereby providing possibilities for developers to engage in diversified application development based on UTXO asset types. Taking the previous Ordinals protocol as an example, many index indexes operate in a centralized manner, and different platforms have different operational standards, leading to discrepancies in asset recognition. If development is based on extending UTXO programmability, then the index can be written as an industry-recognized unified standard, similar to a so-called smart contract format.

Moreover, the concurrent capabilities of the extended UTXO (since each UTXO's spending can be independent, unlike the account model, which can only send transactions one by one) can support many scenarios that require concurrent processing capabilities, thereby aiding the industry's mass adoption.

As for the necessary components of the ecological architecture, I believe the bridge part is very core, namely how to achieve secure asset transfers between the Bitcoin network and L2 networks, while ensuring that L2 networks enjoy the security guarantees of the Bitcoin network. This is a very important module.

Finally, regarding the number and development pattern of Bitcoin L2 networks, my current feeling is that the development of Bitcoin L2 networks has borrowed a lot from Ethereum, so it may not have as many L2 networks as Ethereum. This is not the style of the Bitcoin network. In the future, Bitcoin L2 may release chains compatible with different virtual machines, such as some projects building EVM-compatible networks on the Bitcoin network, some doing Solana virtual machine-compatible networks, and others creating Move language virtual machine-compatible networks. To my knowledge, some are already attempting to build SVM on Bitcoin, as a significant reason is that the Bitcoin L1 network does not have a virtual machine, so L2 networks can adopt different types of virtual machines. Therefore, Bitcoin L2 networks will exhibit greater diversity compared to Ethereum L2 networks. For example, Zulu's L3 network runs an extended UTXO virtual machine, unlike many Ethereum L2 networks that are "reinventing the wheel." Thus, the Bitcoin L2 landscape will definitely be different. If a project wants to achieve more benefits, it needs to innovate in more combinatorial ways in the Bitcoin L2 network rather than simply copying and pasting.

Q: What are the development stages of Zulu, and what important milestones can we expect in the next three to six months?

Cyimon: Overall, it mainly includes three parts.

First, the most important Zulu bridge for the L2 network, which is the bridge aspect;

Second, the release of L3, which cannot be separated from our community members and our technical development team working together for testnet experiences, completing tests as soon as possible. We will also make timely official announcements regarding important activities and technical iterations;

Third, our Zulu team will uphold the entrepreneurial spirit of the Bitcoin community, gradually open-source various mature technologies and functions to facilitate more projects adopting our secure solutions, benefiting more projects in the market, and further enriching the development of the Bitcoin ecosystem.

In terms of timelines, these three parts will be carried out sequentially. Our current goal is to launch the Zulu bridge and testnet in the market before the end of the third quarter of 2024, encouraging more user participation. As for the specific timing, the development of the bridge is a highly challenging technical task, and there are no mature solutions or products to reference, so we are gradually overcoming difficulties. We can only say that we have already achieved the most critical and difficult part, and we still need to iterate on the existing modules to develop challenge protocols and penalty protocols. Once these are completed, the trust-minimized bridge can be launched on the testnet.

Q: In terms of ecological construction, from the perspective of technical developers, what plans or standards will be considered for choosing developers, applications, and partners?

Cyimon: From a technical perspective, regarding partner selection, considering the development of the Bitcoin ecosystem, Zulu is also very eager for more excellent projects and teams to emerge, such as Babylon and Nubit, to address DA issues and the economic security of asset staking, etc.

What Zulu aims to do is to be a "true Bitcoin L2 network," meaning it can help the Bitcoin network achieve functional expansion while enjoying the security guarantees of the Bitcoin network. This security guarantee includes both the economic security of the Bitcoin network and the network security of the Bitcoin network.

Specifically, economic security is formed by staking Bitcoin to create a POS network that protects the correctness of Zulu network's off-chain states. If anyone doubts the existence of issues within the Zulu network, they can initiate challenges on the Bitcoin network, executing the challenge's conclusion on the Bitcoin network. Currently, this is a function that only Zulu can achieve, which is also the focus of our future collaboration with Babylon: they provide a relatively complete asset penalty mechanism, while we serve as the off-chain execution operation network. Additionally, considering the data burden of the Bitcoin network, we also prefer to store data within networks focused on Bitcoin ecosystem DA applications. Therefore, in partner selection, we emphasize mutually beneficial cooperation.

As for the development of the developer ecosystem, I believe it is similar to traditional models. First, Zulu provides a "stage" for developers, which is a very meaningful thing. Once the L3 network is launched, Bitcoin ecosystem developers will be able to engage in diverse development attempts and application explorations. We will also invest a lot of energy and funds to help expand more application scenarios in the Bitcoin ecosystem, especially to conduct more types of fair asset issuance attempts based on extended UTXO types.

Moreover, based on the parallel mechanism, Zulu's L3 network supports the realization of more innovative gameplay, making the so-called mass adoption no longer a distant dream.

Zulu Official Website Interface

Q: In the future, will Bitcoin Lightning payments and the Lightning Network experience rapid development? As the Bitcoin white paper mentions, its original design intention was to be a peer-to-peer payment system, but currently, everyone focuses more on its asset value, viewing it as "digital gold." What are your thoughts on this?

Cyimon: Personally, I believe Bitcoin has already become equivalent to a precious metal asset like gold. Therefore, very few people are willing to trade it back and forth; most people want to hold Bitcoin and find ways to acquire more Bitcoin. Regarding the Lightning Network, I have developers around me working on related matters, and I look forward to them pushing the Lightning Network towards broader applications.

Q: Finally, what is Zulu's ultimate vision, and what milestones are set for different stages? Are they more data-oriented or of another type?

Cyimon: Regarding Zulu's ultimate vision, I would summarize it in one sentence: dedicated to helping the Bitcoin network achieve functional expansion, or in other words, Zulu is the "true expansion layer of the Bitcoin network." The expansion here includes a rich variety of content: performance expansion, cost reduction, and ecological expansion. I would also like to mention that I really like Babylon's market positioning, which is to leverage the economic value of 21 million Bitcoins. In contrast, we prefer to achieve a comprehensive expansion of the Bitcoin network. (Reporter follows up: Does this imply a kind of ecological combinatoriality?)

Cyimon: Yes, regarding different milestones, we focus more on technological iterations and updates because we feel that Bitcoin has fallen behind many other public chains in terms of infrastructure, yet it is the largest ecological network in terms of economic value. Therefore, we will continue to focus on Zulu bridge, L3 network, and Bitcoin ecosystem expansion as our three major goals that need continuous breakthroughs. (Reporter adds: Indeed, this perspective resembles the sense of product updates and iterations like V1, V2, V3 versions.)

Q: Lastly, are there any enlightening stories about the Bitcoin ecosystem or the technical development process that you can share?

Cyimon: Yes, there happens to be an interesting "industry misunderstanding" that I can clarify and express my personal views on, hoping more people can recognize what Zulu bridge's design truly represents, especially regarding the BitVM-related parts. Many projects in the market claim to be built based on BitVM while constructing their bridges, but there is a significant misunderstanding regarding the "BitVM bridge."

The inventor of BitVM, Robin, indeed wrote a bridge design within BitVM. However, this bridge is not the same as Ethereum's bridge; strictly speaking, it is not open to ordinary users for asset transfers. Instead, it focuses on asset issuance, designed more for fixed amounts of inflow and outflow.

For example, it can be understood as a centralized entity issuing an asset on Ethereum, such as WBTC, where users use the bridge based on their trust in this centralized entity, allowing the centralized entity to control this centralized asset. However, the BitVM bridge is designed to facilitate the binding of Bitcoin issued on its L2 network or other chains to have corresponding value on the Bitcoin network itself. Therefore, the BitVM bridge is designed for asset issuance, not for serving ordinary users' asset cross-chain transfers. Of course, Zulu will also release related articles later to explain the specific details and precautions regarding which is used for asset issuance and which is for ordinary user asset transfers based on BitVM cross swaps. But here, I will mention the most intuitive limitation: once a user crosses 1 Bitcoin over, and later through operations, this 1 Bitcoin becomes 1.5 Bitcoins, they cannot cross back because the bridge currently restricts users to only cross back 1 Bitcoin. Therefore, once a user's assets change, this bridge may become unusable, and this mechanism would be rendered ineffective. So, this bridge is not intended for ordinary users.