Kill a new opportunity? What is the controversial Bitcoin Rollup?

The Bitcoin NFT boom brought about by the Ordinals protocol is leading to new changes in the Bitcoin ecosystem, and more and more participants are beginning to discuss the scalability of Bitcoin.

We have introduced Bitcoin layer 2 scaling solutions such as "Lightning Network". In addition to the above solutions, the application of the Rollup protocol on Bitcoin to improve scalability is also attracting more attention.

Bitcoin Rollup

When it comes to Rollup, Ethereum is usually associated with it.

But in October 2022, John Light has published a report

Validity Rollups on Bitcoin, shows the feasibility planning and application method of Rollup protocol on Bitcoin.

Note: The Validity Rollups on Bitcoin report is available at:

Bitcoin builds a relatively simple blockchain architecture, and hopes that all users can run "nodes" on the chain. When necessary or necessary, users can also easily become developers of blocks on the chain.

However, if a blockchain aims to make it easy for "all" users to run full nodes, it must have rules that limit the amount of computation that can be done to validate blocks on the chain.

Such a contradiction is actually a contradiction between decentralization and the scale of computing power distribution. With the development of Bitcoin, this tension has become more and more obvious, and the key solution to ease this tension lies in the improvement of blockchain scalability.

To improve scalability, solutions that are currently receiving high attention include sharding, on-chain optimization, or off-chain channel setting. "Lightning Network" is a solution to build a payment channel under the chain, aggregate it to the chain for settlement, and achieve expansion by reducing the number of transactions; while the solution using the Rollup protocol is a solution that tries to place as little data as possible on the chain. A solution that also keeps transaction execution off-chain.

The difference between the two is that a large amount of transaction data in the "Lightning Network" is stored off-chain, but the deployment of the Rollup protocol is not to process a large amount of transaction data off-chain, it is still an expansion solution for data optimization on the chain .

Bitcoin Rollup hierarchical display example image source/bitcoinrollups.org

The figure above shows the layered application of the Rollup protocol on Bitcoin: there are two Rollup protocols on the second layer of Bitcoin, one is used to provide data availability, and the other is used to provide secure payment and contracts; there are also two Rollup protocols on the third layer of Bitcoin. The 3 Rollup protocols are also used for different use cases, including P2P payments, financial contracts, and game asset transfers.

Rollup type

At present, among the Rollup solutions applied to Bitcoin, the Sovereign Rollup solution (often translated as "sovereign Rollup") is the most discussed solution, which is different from the classic Rollup protocol commonly seen in the past. Is it independent of the main network**.

The solution of applying the classic Rollup protocol, using the first layer of the blockchain (that is, the "main network")** as the data availability layer and settlement layer, the relevant data will not only be stored on the main network, but the second layer related data Also writes to Tier 1. At the same time, transactions are verified by smart contracts on the main network, such as the well-known Rollup projects Arbitrum and Optimism on Ethereum.

Apply Sovereign Rollup's solution, using only layer 1 of the blockchain as an available layer for data, but not using layer 1 to perform settlement. The data stored in the second layer will not be written to the first layer, which has a certain degree of independence. At the same time, the transaction is verified by the nodes on Sovereign Rollup, that is, the layer 2 where Sovereign Rollup is located is used for execution settlement.

Sovereign Rollup's hierarchical structure diagram on the chain & verification logic display diagram Source/celestia.org

The value of the Sovereign Rollup mode of operation is that whether the first-tier mainnet is hacked or needs technical upgrades, the second-tier will not be affected; secondly, the second-tier has not lost the data security and security of the first-tier. Censorship resistance - this mode of operation is undoubtedly more desirable for Bitcoin, a blockchain with limited mainnet computing power.

Learn about Rollkit

Interest in the Sovereign Rollup in the Bitcoin community arose in March 2023.

At that time, Rollkit, an open source technology framework developed by Celestia, had just announced the completion of a research that could store Rollup data directly on the Bitcoin chain. Developers have since been able to use Rollkit to deploy the Rollup protocol on top of Bitcoin to improve scalability and minimize network operating costs.

One of the biggest features of the Rollkit framework is that it allows developers to customize the data availability layer and execution layer, and supports developers to deploy Sovereign Rollup.

Rollkit modular development framework diagram source/rollkit.dev

Application Outlook

The active application deployment of Rollup on Ethereum has gradually changed blockchain users' perception of transactions, data storage, and on-chain verification on Ethereum.

Although the deployment of Rollup on Bitcoin is still in its infancy, with the evolution of development tools such as Rollkit, Rollup may also bring more new paradigms worth exploring to the Bitcoin community in the near future.