The Race for Programmable Bitcoin: BitVM Arms Race in High Gear

The quest to programmably extend Bitcoin without soft-fork upgrades has ignited one of crypto’s most dynamic, creative “arms races.” At the center of the action is BitVM.

BitVM: Evolving Bitcoin’s Provable Computation Framework

BitVM (proved Bitcoin VM) facilitates proving complex off-chain computations on Bitcoin using fraud proofs. The framework has seen two iterations:

• BitVM1: The original version employed a multi-round interactive protocol for fraud proofs.
• BitVM2: A significant simplification to a single-round fault proof, utilizing a split SNARK (Succinct Non-Interactive Argument of Knowledge) verifier. This iteration is already being explored by pioneers like Build on Bitcoin (BOB) and Citrea.

BitVM3: Ambitious Reductions, Significant Challenges

The latest iteration, BitVM3, pushes the boundaries further, with the ambitious goal of slashing on-chain fraud proof costs by roughly 1,000x. However, BOB co-founder Alexei Zamyatin cautions that BitVM3 remains fundamentally under development:

“The overall design of the BitVM bridge between BitVM2 and BitVM3 remains the same. The key difference is swapping the SNARK verifier (BitVM2) with a garbled circuit (BitVM3)…”

Garbled circuits are cryptographic tools where one party pre-commits to a computation that can be verified by another without revealing the private inputs. Promisingly, this could exponentially reduce the Bitcoin on-chain footprint for each logic gate.

Despite the promise, garbled circuit implementation on Bitcoin faces hurdles: current research indicates it requires substantial further work before production deployments, addressing complexity, security, and data availability challenges.

In the Trenches: BitVM2 Poised for Deployment

If BitVM3 remains aspirational research, BitVM2 is moving towards concrete implementation.

“It is important to note that the majority of the work to build a bridge using BitVM stays the same [when] using BitVM2 or BitVM3.”

Meanwhile, Zamyatin estimates pessimistic worst-case on-chain fraud proof transaction costs for BitVM2 at around $16,000, cheaper than BitVM proof costs on other chains like Ethereum. Test nets are launching.

Garbled Circuits vs. Other Snouts

Other teams are exploring garbled circuit permutations:

• Citrea’s Approach: Classic Yao-style garbling combined with cut-and-choose verification. Straightforward, security-focused, but currently more resource-intensive.
• Alpen Labs’ Approach: Exploring designated-verifier SNARKs, trading communication overhead for dense cryptography that marries better performance but relies on newer, less tested techniques.

Dependence on New Opcodes: Path to Simpler Scaling?

The entire BitVM progression could become significantly more efficient if the Bitcoin Core developers approve soft-fork opcodes directly into Bitcoin, bypassing the need for complex Bitcoin multisig setups.

However, consensus progress remains agonizingly slow. While CTV (Covenant Type Witness‘) is generating more favorable chatter than a recent BEHOLD proposal less supportive of the BitVM ecosystem.

Conclusion: A Future Layer 2 Scaling

While BitVM3 represents thrilling theoretical progress, its scalability ambitions hinge on future proof research. For near-term execution, BitVM2 bridges and similar approaches appear destined to be Bitcoin’s next major stride towards trust-minimized layer 2 scaling. Breakthroughs via soft-fork opcodes, however, would undoubtedly accelerate this journey.