Deep Dive into Bitcoin DA Adapters Chainway and Kasar Labs: Does Bitcoin Need ZK Rollup?
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Deep Dive into Bitcoin DA Adapters Chainway and Kasar Labs: Does Bitcoin Need ZK Rollup?
At its core, Bitcoin is not necessary.
Navigating Web3 tides with focused insightsAuthor: Namcios
Compiled by: TechFlow
Bitcoin is about to get zero-knowledge (ZK) Rollups. Recently, two distinct projects have turned this development into reality—an advancement that could not only help Bitcoin scale more effectively but also offer additional privacy guarantees for users choosing to adopt it.
Last week, Chainway announced the open-sourcing of its data availability (DA) adapter—a technology enabling developers to leverage Bitcoin’s security and finality when building Rollups using the Sovereign software development kit (SDK). Sovereign offers bundled services for developers aiming to construct various types of Rollups, and Chainway's release aims to enable Bitcoin’s first ZK Rollup.
Coincidentally, Kasar Labs in collaboration with Taproot Wizards has simultaneously released a DA adapter for Bitcoin. This adapter allows developers to integrate the Madara stack into Bitcoin to run Starknet Rollups based on Cairo, the programming language created by StarkWare.
What Is a ZK Rollup?
Rollups batch non-standard Bitcoin transactions—such as those from certain sidechains—and publish them into blocks on the base blockchain (like Bitcoin). This significantly reduces the computational cost of validating these transactions while still benefiting, to some extent, from Layer-1 blockchain security. In this sense, Rollup transactions exist on Bitcoin. Users then run a node for that sidechain, which knows how to interpret the data published onto Bitcoin and reconstruct account balances. However, this requires everyone to run a full node of the alternative protocol—an approach that is inherently unscalable. This is where ZK comes in.
ZK Rollups utilize zero-knowledge proofs—a cryptographic method ensuring computational integrity without compromising privacy. It enables a prover to mathematically convince a verifier of the correctness of a computation statement without revealing any specific details used in computing that proof. In the context of Rollups, this is crucial because it means observers need only see the final proof to verify the statements or transactions. Using ZK proofs, participants in a Rollup can obtain mathematical certainty about the latest state directly from Bitcoin while maintaining full privacy.
Benefits of ZK Rollups include the ability for users to receive payments without being online—simply retrieving payment data from the chain when possible—no need to manage liquidity, and independence from low fees on Bitcoin’s base layer. Additionally, ZK Rollups allow developers to add any desired programming environment atop Bitcoin, such as Turing-complete smart contracts.
ZK proofs rely on two main mathematical techniques: SNARKs and STARKs. The former, Succinct Non-Interactive Arguments of Knowledge, predates the latter and has been applied in cryptocurrencies like Zcash, offering high levels of user privacy. Scalable Transparent Arguments of Knowledge were developed later, aiming to provide better security and scalability atop the desired privacy features. This is because SNARKs depend on a trusted setup to generate proofs, whereas STARKs are designed to be trustless. Finally, SNARKs are vulnerable to quantum computing attacks, while STARKs are quantum-resistant.
Given Bitcoin’s nearly flawless track record and resistance to deep reorganizations, it is the most suitable cryptocurrency for hosting Rollup transactions—since Rollups depend on the main chain to access critical data needed for spending. The main chain also ensures that the Rollup remains active and accessible.
To properly implement ZK Rollups on Bitcoin and allow users to trustlessly bridge their Bitcoin between Rollups, a soft fork would be required. This soft fork would add a new opcode to the oldest cryptocurrency, enabling Bitcoin itself to recognize and validate ZK proofs. If implemented, users would only need to run a Bitcoin node to trustlessly verify proofs published by a specific Rollup, check their accounts and balances, and withdraw funds from the Rollup.
The two projects mentioned earlier do not assume any consensus changes to Bitcoin. Instead, they leverage the Ordinals protocol to avoid requiring new opcodes. More specifically, they use the concept of inscription envelopes introduced by Ordinals—an innovation allowing developers and users to encapsulate any type of data using specific markers and several opcodes. In Ordinal inscriptions, this marker is "ord".
The marker and opcodes at the beginning of an envelope serve a dual purpose. First, they signal to Bitcoin nodes that they can skip over information envelopes unrelated to the Bitcoin network. Second, they act oppositely for users and applications aware of the envelope format—indicating that the content inside is relevant to them. In the case of ZK Rollups, users can scan Bitcoin blocks for these envelopes, learn about the latest Rollup state, and cryptographically verify it using ZK proofs.
Now that we understand ZK proofs, let’s return to the two projects mentioned earlier and explore the unique aspects of their designs.
SOVEREIGN
The Sovereign SDK itself has three primary goals. First, it aims to provide a standardized interface for communication between Rollups and the DA layer, making it easier to deploy Rollups on new DA layers and enabling new chains to support existing Rollups. Second, it integrates with cryptographic compilers to transform business logic code into cryptographically verifiable forms. Third, it provides default implementations of common blockchain primitives such as tokens, non-fungible tokens (NFTs), and cross-chain bridges.
As previously mentioned, Chainway’s DA adapter is designed to make it easier for applications built with the Sovereign SDK to connect to Bitcoin. In other words, the adapter enables Sovereign Rollups to use Bitcoin as their DA layer—a capability that was previously impossible. Data availability is essential for Rollups because it allows off-chain computations to be trustlessly verified and is a prerequisite for users to validate or modify their balances and withdraw funds from the Rollup.
For Sovereign Rollup transactions to be included in Bitcoin blocks, users submit their transactions to what is known as a sequencer. In Chainway’s DA adapter design, the sequencer is operated by the foundation itself and is responsible for establishing the connection between the sidechain and Bitcoin, ensuring all user-submitted transactions are published onto Bitcoin in the form of ZK proofs.
This may sound somewhat centralized—and indeed, it is. However, given the existence of validity-proof technology—specifically ZK-STARKs—the sequencer cannot act maliciously. This is because proofs privately confirm transaction legitimacy, and anyone can independently verify them. For example, the sequencer cannot steal user funds or execute unauthorized transactions. That said, theoretically, it could censor user transactions by refusing to include them in Bitcoin blocks and withholding the data. In such cases, users retain the option to publish their transaction data directly to Bitcoin by recording that information on-chain.
Chainway has stated that in the future, they plan to achieve decentralized sequencing through a small group of sequencers, with participation being permissionless and based on staking.
STARKNET
Like Sovereign, Starknet also aims to enable Rollup construction. However, Starknet is a more opinionated ecosystem, featuring clearly defined components such as Cairo, CairoVM, and Madara that developers can use to build upon.
Starknet is currently a ZK Rollup running on Ethereum, meaning it relies on Vitalik Buterin’s blockchain as its data availability layer. It uses STARK proofs to deliver the necessary privacy and security assumptions for users, along with improved scalability and lower transaction costs achieved by batching transactions before publishing proofs and new states to Layer-1. Cairo is a Turing-complete programming language for writing provable programs, where one party can prove to another that a computation was executed correctly without requiring the latter to re-execute the program. It is the first production-grade platform for generating STARK proofs for general-purpose computation.
The Cairo Virtual Machine receives bytecode generated by the compiler and executes it on a computer. The output of execution is a trace of the program, which can then be sent to a STARK proof generator to prove the validity of statements expressed in the Cairo code.
Madara serves as the sequencer for the Starknet stack, helping developers support ZK Rollups based on Starknet.
Until recently, this entire software stack was only available on Ethereum. Now, Kasar Labs and Taproot Wizards have launched a DA adapter for Bitcoin, designed to allow developers to anchor Rollups built using the open-source version of Starknet onto the original and most secure cryptocurrency network.
Does Bitcoin Need ZK Rollups?
In essence, Bitcoin does not need them. It functions extremely well in its current state, and there is little reason to believe Bitcoin needs significant changes. On the other hand, scalability is a real demand, and technologies like the Lightning Network have already proven useful in enabling more participation in Bitcoin’s economic activity for users who otherwise couldn’t participate.
ZK Rollups offer a different way of viewing Bitcoin. The two projects discussed above do not require any actual changes to Bitcoin itself. However, to unlock the full potential of this technology, a consensus change introducing a new opcode would be necessary. For now, research into ZK-based Rollup technology is pushing the boundaries of what’s possible with Bitcoin—an effort beneficial for expanding the Bitcoin user base, much like the Lightning Network did.
Similar to the Lightning Network, Rollups function by bundling multiple transactions together and publishing a single data source to Bitcoin. Of course, ZK Rollups take a very different technical approach—and rightly so. This technology isn’t trying to compete with the proven, low-cost second-layer payment systems that Bitcoin users already love. Instead, Rollups focus on different problems and aim to provide alternative solutions.
For those wishing to do more on Bitcoin, a scaling solution capable of enabling private, complex computations secured by mathematical proofs sounds appealing. Even so, fully trustless bridging of Bitcoin into and out of Rollups will ultimately depend on that new opcode. But even without it, the idea is now in motion.
It remains unclear whether ZK Rollups will gain any traction on Bitcoin. Bitcoin already has a sidechain—Liquid—that has operated on Bitcoin for years, yet its transaction volume remains low. Arguably, Liquid’s federated model has been a drawback, giving ZK Rollups a potential advantage in this regard. Perhaps Rollups might suffer the same fate as Liquid—low volume and low interest—as Bitcoin users continue to prefer simply “HODLing Bitcoin.” Or, they might usher in a new chapter in Bitcoin’s evolution and usage.
Regardless of whether the outcome is success or failure, pursuing high-quality research in this space is a natural and necessary endeavor. Whatever the result, new knowledge will be gained. One thing is certain—Bitcoin will keep hashing and producing blocks, allowing all users to enjoy the monetary certainty of hard money, regardless of any of these developments.
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