Zero-knowledge (ZK) rollups, a technology that allows for a significant scaling of Bitcoin while maintaining privacy, are set to revolutionize the original cryptocurrency. Two separate projects, Chainway and Kasar Labs, have taken steps to make ZK rollups a reality.
Chainway has announced the open-source release of their data availability (DA) adapter, a crucial piece of technology that enables developers to leverage Bitcoin’s security and finality to create rollups with the Sovereign Software Development Kit (SDK). This launch aims to enable Bitcoin’s first ZK rollup.
In a similar vein, Kasar Labs has partnered with Taproot Wizards to release a DA adapter for Bitcoin. This adapter allows developers to integrate the Madara stack into Bitcoin and run a Starknet-based rollup using the Cairo programming language created by StarkWare.
So, what exactly are ZK rollups? Essentially, rollups bundle non-standard Bitcoin transactions, such as those for sidechains, together and publish them on the main blockchain, like Bitcoin. This process significantly reduces the computational cost of verifying these transactions while benefiting from the security of the Layer-1 blockchain.
ZK rollups rely on zero-knowledge proofs, a cryptographic technique that ensures integrity without compromising privacy. With zero-knowledge proofs, a prover can confirm the correctness of a computational statement to a verifier without revealing the specific information used to compute the proof. This feature allows any observer to verify the statements or transactions by only knowing the final proof, ensuring privacy for those using the rollup.
The advantages of ZK rollups include the ability for users to receive payments without needing to be online and the elimination of liquidity management. Furthermore, ZK rollups are not dependent on low fees on the Bitcoin base layer, and developers can add any desired programming environment on top of Bitcoin.
There are two main mathematical tricks used for ZK proofs: SNARKs and STARKs. SNARKs provide a high level of privacy to users and are used in cryptocurrencies like Zcash. On the other hand, STARKs focus on better security, scalability, and privacy. Unlike SNARKs, STARKs are post-quantum secure, making them resistant to quantum computing attacks.
Given Bitcoin’s history of impeccable uptime and resistance to deep reorgs, it is ideal for rollup transactions that rely on the mainchain for accessing crucial data. The mainchain also ensures the availability and functionality of the rollup.
To implement ZK rollups properly on Bitcoin and establish trustless bridges between BTC and the rollup, a soft fork would be necessary. This fork would introduce a new opcode to Bitcoin, enabling native support for verifying ZK proofs. If this were to occur, users would only need to run Bitcoin nodes to verify the proofs posted by a rollup and manage their accounts and balances.
The projects mentioned earlier, Chainway and Kasar Labs, do not assume a consensus change to Bitcoin. Instead, they leverage the Ordinals Protocol, specifically the concept of inscription envelopes. Inscription envelopes allow developers and users to encapsulate data using a specific flag and a few opcodes. For ZK rollups, users can scan Bitcoin blocks for these envelopes to verify the rollup’s latest state using the ZK proof.
Let’s delve into the unique aspects of the designs of the two projects:
Sovereign: The Sovereign SDK aims to provide a standard interface for rollups to communicate with DA layers, simplify deployment on new DA layers, and support existing rollups. It integrates cryptographic compilers to convert code into cryptographically verifiable form and offers default implementations of common blockchain primitives.
Chainway’s DA adapter makes it easier to connect Sovereign applications to Bitcoin. It allows Sovereign rollups to leverage Bitcoin as their DA layer, enabling trustless verification of computations outside the main chain. Transactions from Sovereign rollups are relayed to a sequencer, which ensures their publication to Bitcoin with ZK proofs. Although this process may seem centralized, the presence of validity proofs makes it impossible for the sequencer to act maliciously.
Starknet: Starknet also facilitates the development of rollups but with a more opinionated ecosystem. It relies on Ethereum as its DA layer and utilizes STARK proofs for privacy, security, scalability, and lower transaction costs through transaction batching.
Both projects leverage the unique features of their respective protocols to enable the implementation of ZK rollups without requiring consensus changes to Bitcoin.
ZK rollups represent a significant step forward in scalability and privacy for Bitcoin. With the development of innovative technologies like Chainway’s DA adapter and Kasar Labs’ collaboration with Taproot Wizards, the future of Bitcoin as a privacy-focused, scalable cryptocurrency is becoming increasingly promising.
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