A surprising proposal that is already causing a lot of talk, called " BitVM » could potentially profoundly transform the Bitcoin ecosystem. Recently announced by the developer Robin Linus who is currently working at ZeroSync, this proposal offers exciting prospects for the development of Bitcoin applications using so-called Zero Knowledge Proof.
Thus, BitVM would make it possible to introduce virtually any arbitrary calculation into the Bitcoin ecosystem that would be executed off-chain. BitVM presents itself as a computing paradigm that allows turing-complete contracts to be expressed on Bitcoin without the need for any modification to the network's consensus rules. To summarize BitVM, we can say that it would be a kind of extension that would allow Bitcoin to do more sophisticated calculations without modifying it.
The most notable aspect of BitVM is that it does not require any changes to the existing Bitcoin consensus. It is also on this precise point that the proposal is seen as interesting by a majority of the Bitcoin community who do not wish to modify the protocol or overwhelm it with transactions perceived as useless. However, other members remain skeptical about the innovation that BitMV entails.
BitVM’s technical proposal
To understand how this works, it’s essential to delve into the foundations of the proposition. First of all, it is important to know that computer calculation, including Bitcoin transactions, relies on basic logical operations performed by logic gates. Logic gates take binary values (1 or 0) as input and produce a binary value as output based on a simple logic operation. BitVM is based on a logic gate called a "NAND gate," which can perform all the necessary logic operations.
To construct a NAND gate in the Bitcoin script, BitVM uses hashlocks and two specific opcodes: OP_BOOLAND and OP_NOT. THE hashlocks are fork scripts that can be spent in two different ways, by revealing the preimage of a specific hashlock. One of these ways puts a 1 on the stack, while the other puts a 0. This allows these hashlocks to be used to "unlock" a bit for the input of a NAND gate.
BitVM then uses OP_BOOLAND and OP_NOT to perform logical operations. OP_BOOLAND produces a 1 as output if both of its inputs are 1s, while OP_NOT inverts the input value (1 becomes 0 and vice versa). By combining these opcodes with the hashlocks, BitVM can perform NAND operations within the Bitcoin script, verifying that the output matches what the user claims.
The revolutionary aspect of BitVM lies in its ability to build complex circuits using these NAND gates. Users can slice any arbitrary computation into a series of NAND gates, then encode each gate into a tree of taptrees that can be locked with a UTXO. They then pre-sign a series of transactions for a challenge and response game that can be run on-chain.
The idea is that the complex calculation is first verified off-chain, but in case of disagreement or behavior that would be deemed dishonest, it can be challenged on-chain. According to the author, they would be verified in the same way as what is done with "optimistic rollups".
What are the doubts regarding bitVM?
Although the proposal seems promising in that it will be easier to create programs on the Bitcoin network without modifying it, there are still challenges to overcome. For example, managing the enormous amounts of data generated by BitVM is a major challenge. Indeed, the cost of managing off-chain data would be absolutely colossal. Some then question the merits of such an initiative. This, for example, is what has been criticized for the concept of Ordinals and this is a sore point for Bitcoin users.
The other problem that BitMV raises is that this solution only works between two parties (the one who proves and the one who verifies), which limits its usefulness in certain cases. There will certainly be additional research to generalize with several participants.
Final word on the contribution of BitVM
Ultimately, BitVM represents a significant advancement in the Bitcoin field by allowing the introduction of arbitrary calculations while preserving the integrity of the Bitcoin network. Thus, thanks to BitVM, it would be possible to consider more advanced calculations which would only have been possible by performing softforks for example.
Some even go so far as to say that it is the end of altcoins on other blockchains and that everything will now be done on Bitcoin.
Although issues remain, this proposal is generating great interest in the Bitcoin community and deserves continued attention.
BitVM might just be the ultimate innovation that Bitcoin needs to evolve into new possibilities for using Bitcoin.
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