Does the BitVM white paper imply that the Bitcoin network can replicate all narratives of ecosystems like Ethereum?

Author: Haotian

A white paper titled "BitVM: Compute Anything On Bitcoin" has sparked heated discussions among developers, seemingly indicating that the Bitcoin network can achieve Turing-complete contracts and execute any computable function.

Does this mean that the Bitcoin network can replicate all narratives of ecosystems like Ethereum? Moreover, it does not require changing the existing Bitcoin consensus or even any upgrades; it can endow the Bitcoin network with "complex" programmability solely based on the current Bitcoin op_codes, allowing it to perform Turing-complete computations?

Wait, let's not get ahead of ourselves. First, let's explore the conceptual path of BitVM. How does the Script space execute complex programming? What does the Optimism Rollup concept refer to? What is the principle of Fraud Proof? What obstacles exist for the implementation of BitVM? Next, we will analyze its general logical framework step by step to facilitate understanding. (We won't delve too much into specific technical implementation details.)

How to Achieve Complex Programmable Features?

Due to the very limited programming capabilities of Bitcoin, which only supports simple logic and a limited set of op_codes in script scripts, it is impossible to develop complex smart contracts on the Bitcoin network. The core point of the BitVM proposal is that it achieves various program instructions similar to binary circuits through a taproot address matrix or taptree, which together equate to a complete contract execution.

Specifically, we can treat each UTXO spending condition instruction in a Script script as the smallest unit of a program. A script execution results in either true or false. If certain code is input into the taproot address, it can yield a deterministic 0 or 1. By combining a large number of taproot addresses into a matrix, we can form an ordered taptree, and the execution results can produce a lot of binary circuit text effects like 011001, which can be viewed as an executable binary program. The complexity of the program depends on the number of combined taproot addresses; the more addresses there are, the richer the pre-set instructions in each Script within the Bitcoin framework, and the more complex the entire taptree can execute.

This idea is indeed quite ambitious. However, according to this logic, the smallest unit instructions are indeed completed by Bitcoin full nodes, and the infinite combination of taproot addresses can lead to many complex calculations. To some extent, it is not an exaggeration to say it is Turing complete. But the infinite combination of taproot addresses will only increase cost consumption; theoretically, it can achieve Turing completeness, but it is impractical.

Therefore, the mention of Turing completeness in the white paper is merely a statement under extreme ideal conditions, which raises some suspicion of "conceptual substitution." Even Ethereum, which claims to be a supercomputer, cannot fully achieve Turing completeness, let alone the Bitcoin network that relies solely on scripts.

A Brief Analysis of Several Complex Concepts

Based on the understanding of the core framework above, let's revisit the concepts mentioned in the white paper, such as Optimism Rollup, Fraud Proof, and Bit commitment, and what Logic Gates are. Since a single taproot space and executable code logic are limited, executing complex programs off-chain and placing only the key verification steps on-chain is essentially a form of Rollup thinking, right?

Fraud Proof can be understood this way: the Prover and verifier first compile a huge binary circuit. When the Bitcoin network executes the circuit, a prerequisite is that the Prover must pre-sign and stake a certain amount of Bitcoin assets. If the Verifier finds that the Prover has malicious intent, they can similarly send a transaction to the chain to trigger the UTXO unlocking conditions of the on-chain taptree "program." If successful, the verifier can confiscate the Prover's staked assets, effectively completing a fraud proof process.

In this logic, it is not difficult to understand why BitVM is only suitable for two parties with a consensus agreement; that is, they must share the total circuit diagram before execution, must execute the fraud proof program within a valid period, and must stake certain assets and pre-sign. If both parties do not collaborate off-chain to establish a set of agreed consensus, relying solely on the limited on-chain execution environment of the Bitcoin network, it is challenging to facilitate a true "contract" execution.

What Obstacles Might BitVM Face in Implementation?

1) BitVM is currently only suitable for on-chain operations between two parties with a consensus agreement; the on-chain environment is merely the process of executing contracts transparently. Currently, it can only be realized between two agreed parties; achieving N-N would require more complex technical logic design.

2) How BitVM applies the script of a single taproot address to implement the smallest programming unit cannot exceed the execution logic framework of Bitcoin, such as hashlock, timelock, etc. It cannot exceed the limited storage conditions. In an optimistic scenario, a taproot address can program hundreds of logic gates; more would require combining a large number of addresses to construct a taptree. The problem arises that executing the preset unlocking conditions of taproot addresses requires paying miner fees, and the more addresses combined, the greater the cost incurred. In the future, perhaps the bidirectional channel technology of the Lightning Network can reduce costs, but overall, relying on the Bitcoin network to execute logic gate circuits is not only slow but also a costly endeavor.

3) The ideal scenarios supported by BitVM are very limited and are more suitable for heavy off-chain computation; only certain consensus and asset transfer scenarios need to rely on the chain, such as asset disposal in games, etc.

Overall, BitVM is a highly creative and ambitious concept, but based on its implementation technical framework, it is likely to remain in the conceptual stage of the white paper in the short term. The exploration of long-term application scenarios and practical implementation still faces significant challenges. To illustrate with a simple analogy: BitVM is like building a giant computer larger than a room in an era where everyone can use mobile terminals.

Note: The above interpretation is only applicable for understanding the general technical framework of BitVM, to help everyone grasp the underlying technical logic. Specific practical methods may vary, and if there are technical experts with in-depth research on technical details, they can correct and supplement in the comments.