The year 2023 was rich in development for the Bitcoin network. Indeed, it saw the emergence of Ordinals and then BRC-20s. This opened up new possibilities on Bitcoin. In particular, introducing NFTs via Ordinals and fungible tokens via BRC-20s. Finally, at the end of the year, the introduction of BitVM made it possible to consider the creation of L2 on Bitcoin. Now, BitVM is evolving with the publication of BitVM2 on Bitcoin.

BitVM: a revolutionary solution

Since its inception, Bitcoin has stood out for its robustness and simplicity. However, this simplicity has also led to some limitations, particularly in terms of programmability.

Unlike Ethereum, whose virtual machine (EVM) allows the execution of complex smart contracts, Bitcoin was designed with a limited scripting language, unable to support so-called Turing-complete smart contracts. However, this limitation has not discouraged developers.

Thus, on October 9, 2023, BitVM was born from the hands of Robin Linus. It is an approach that allows Turing-complete contracts to be executed on the Bitcoin network. And this, without requiring any modification of the Bitcoin consensus or code. A central component, because the ossification of Bitcoin is a central feature of the project.

BitVM introduces a new way to use Bitcoin as a kind of universal calculator. Instead of performing calculations directly on the blockchain, BitVM relies on optimistic verification of the results.

The principle is simple. A prover (the participant wishing to execute a contract) performs an off-chain calculation and claims that the result is correct. A verifier (the other party to the contract) then has the possibility to contest this result by providing an on-chain proof of fraud, in the event that the calculation turns out to be incorrect. This verification model based on proofs of fraud is inspired by the optimistic rollups already well known in the Ethereum ecosystem.

A limited system

However, BitVM is not without limitations. The current model is restricted to a two-party framework, where a prover interacts with a verifier. Additionally, the complexity of off-chain computation and the communication required between parties can pose challenges for large-scale implementations. Despite this, BitVM ushers in a new era for Bitcoin.

The craze was such that several second-layer solutions for Bitcoin have already integrated BitVM into their system. This is notably the case of L2 Citrea,

BitVM2: BitVM but stronger

On Thursday, August 15, against all expectations, Alexei Zamyatin unveiled the BitVM2 whitepaper on the social network X. BitVM2 is presented as a “major improvement over previous versions of BitVM.”

The post is accompanied by a link to the whitepaper titled “BitVM2: Bridging Bitcoin to Second Layers.”

In practice, BitVM2 was made by Robin Linus, the creator of BitVM. He is joined by Lukas Aumayr, Alexei Zamyatin, Andrea Pelosi, Zeta Avarikioti and Matteo Maffei.





BitVM2 features several significant improvements designed to expand the computing capabilities on Bitcoin while optimizing the efficiency and security of the protocol. Let’s explore BitVM2’s evolutions together.

Challenges sans permission

One of the major innovations of BitVM2 is the introduction of permissionless challenges.

So, on BitVM, only specific actors could initiate challenges, i.e. contest evidence.

BitVM2, on the other hand, allows any user to challenge the results of the calculations, making the system more robust and decentralized.

Therefore, any user, owning a full Bitcoin node, can challenge an operator. This paves the way for permissionless proof management, where any user can challenge an operator’s claim, thus strengthening the security of the protocol.

As a reminder, a challenge is a verification mechanism where a user questions the validity of a calculation carried out off-chain by an operator.

The system is based on a proof-of-fraud model, where the prover, i.e. the party performing the computation, asserts that the result is correct. If the verifier or any other user believes that the prover is lying or has made a mistake, they can initiate a challenge.

This triggers an on-chain procedure where the prover must demonstrate the correctness of its calculation. If the prover fails to prove its good faith, the challenger wins and the prover is penalized, thus ensuring the integrity of the protocol. This system of challenges and proofs is already widely used by the various Ethereum rollups.

Reduction in the number of on-chain transactions

This new version also improves the efficiency of the protocol. To do this, it drastically reduces the number of on-chain transactions required to resolve disputes.

While BitVM could require up to 70 transactions to complete a verification, BitVM2 reduces this to just three transactions, making the process not only faster, but also more economical in terms of transaction fees.

Introduction des SNARKs

That’s not all! BitVM2 now integrates SNARKs. This allows you to verify complex calculations in a more concise and secure way.

Thus, BitVM was limited to simple fraud proofs in a two-party context. On the other hand, version 2 improves the fraud proof capability by integrating SNARKs, allowing to verify complex computations using fewer resources.

For this, BitVM2 uses a SNARK verifier implemented in the Bitcoin script, which is divided into manageable chunks that can be processed in Bitcoin transactions. This allows for compact verification of fraud proofs.

Improving bridge safety

So far, BitVM has mostly been used and explored in the context of creating a bridge between Bitcoin and an L2. However, in the context of BitVM, bridges required an honest majority among signers to ensure security.

A limitation that could be circumvented with BitVM2. So, where BitVM relied on an honest majority of signers to ensure the security of funds, BitVM2 reduces this requirement to simple honesty during the initial setup. Thereafter, the solution only requires an active and honest operator to maintain security.

During the initial setup, a set of actors is formed to set up the rules and transactions that will be used to execute contracts. The notion of “simple honesty” means that for the system to be secure, it is sufficient that at least one of the signatories is honest during this initial setup. This honest actor guarantees that the transactions or scripts created do not contain any flaws or malicious conditions.

This development is particularly important for second-layer solutions, which can now leverage BitVM2 to provide more secure and efficient bridges between Bitcoin and other blockchains.

As you will have understood, BitVM2 introduces many improvements in comparison with BitVM. These latter could well accelerate the rise of sidechains and other rollups on Bitcoin.

In July, the BitcoinOS project achieved the feat of verifying the first zero-knowledge proof on Bitcoin. A feat that was achieved without any modification to the Bitcoin code. These developments and those introduced by BitVM2 predict a second part of 2024 likely rich in developments for Bitcoin.#Bitcoin❗ #BinanceTurns7 #trainding