✓ Introduction:

BitVM is a “Computing paradigm to express Turing-complete Bitcoin contracts” proposed by Robin Linus, which does not require a soft fork.

Bitcoin script is designed to be Turing-incomplete, making it impossible to implement arbitrary contracts like those implemented on VM-based chains. Previous proposals to realize Turing-complete contracts on Bitcoin required a soft fork to activate new opcodes. BitVM is different from these proposals as it does not require one.

Please note that it still has important limitations:

・Contracts are limited to those between two parties

・A significant amount of computation and interaction between the two parties is required (i.e., Hundreds of MB to several GB data interaction; local storage)

Despite these constraints, the proposal has spurred vibrant community debate.

✓ What is BitVM??

BitVM, short for Bitcoin Virtual Machine, is a proposed virtual engine that seeks to bring complex smart contract-like functionality to Bitcoin without making any changes to the protocol.

It will give Bitcoin the option to mimic functionalities normally known from Turing-complete blockchains like Ethereum. Turing completeness in blockchains refers to the capability of a blockchain's programming language to execute any computable function, allowing for the creation of complex and diverse smart contracts and decentralized applications (dApps).

However, Bitcoin’s virtual machine differs from a “full VM” like the Ethereum or Solana Virtual Machine because it can only support two-party transactions instead of multi-party transactions beyond two participants.

Also, BitVM performs most computations off-chain to avoid clogging the network. Conversely, common VMs like the Ethereum Virtual Machine (EVM) are integrated into the blockchain and conduct computations on-chain.

Although BitVM will help Bitcoin handle Turing-complete smart contracts, BitVM contributor Sam Parker observes that the proposed virtual machine will not make the blockchain any more Turing-complete in the technical definition than it is now.

Rather, BitVM will increase the length of the programs that one can run on Bitcoin, making the blockchain Turing-complete enough for smart contracts or programs to be executed.

A system is considered Turing-complete if it can carry out any computation given enough resources and time. Native Bitcoin smart contracts are simple and not Turing-complete.

Robin Linus released BitVM’s whitepaper on October 9, 2023. Linus is the Project Lead of ZeroSync, an organization focused on scaling Bitcoin with zero-knowledge proofs. BitVM’s first proof-of-concept was developed by the pseudonymous developer Super Testnet.

HOW DOES BITVM WORK?

BitVM acts as a middle layer that minimizes on-chain footprint by performing computations off-chain. Like optimistic rollups, the VM bundles multiple off-chain transactions and posts them to the base layer for storage.