GOAT Network released the GOAT BitVM2 White Paper, reducing the challenge period from 14 days to 1 day, accelerating the implementation of Bitcoin zkRollup.

GOAT BitVM2 uses the Bitcoin network as the settlement layer and builds a decentralized sorter network as the computation layer.

Source: GOAT Network

The GOAT Network officially released the GOAT BitVM2 white paper, proposing the first feasible Bitcoin-native zkRollup protocol. This protocol builds upon the advantages of the original BitVM2 protocol while introducing multiple innovations, systematically addressing key issues in security, challenge mechanisms, and economic incentives, laying the foundation for the scalability and programmability of the Bitcoin ecosystem.

The Potential and Real Bottlenecks of BitVM2

The BitVM2 protocol proposed by Robin Linus and the ZeroSync team in 2024 is an innovative path that allows for the on-chain verification of arbitrary computations without changing the Bitcoin mainnet protocol, creating possibilities for Bitcoin zkRollup and cross-chain bridges. However, there are still the following key issues when moving toward practical applications and using BitVM2 for production-level cross-chain bridges:

• Operator (Operator) Double-Spend Attack: BitVM2 currently allows operators to submit verifiable but in fact fraudulent states (e.g. from forked chains), which could trigger the risk of a double-spend attack when a user withdraws.
• Challenge process is inefficient: The existing mechanism uses one-to-one ( staking, challenges ) relationships, and has a lengthy challenge cycle, leading to high computation and coordination costs. At the same time, it does not support flexible withdrawal amounts, reducing capital utilization and user experience.
• Lack of effective incentive mechanisms: The protocol lacks effective incentives to drive the participation of various roles in the Rollup ecosystem, especially challengers who often do not receive rewards, leading to insufficient willingness to honestly and timely initiate challenges. In systems that rely on crowdfunding incentives, there may also be issues where rewards are allocated to the wrong participants, further undermining the accuracy and effectiveness of incentives.

GOAT BitVM2: Three Major Mechanism Innovations

GOAT Network, from an engineering perspective, has launched the GOAT BitVM2 enhancement plan and has deployed it as the core execution system of GOAT Network, marking the first practical implementation of Bitcoin zkRollup. This plan revolves around fundamental improvements in three mechanisms:

1. Cryptoeconomic Security Layer

Combining the native Script verification of Bitcoin and the dual punishment mechanism of the GOAT network consensus layer significantly increases the cost of malicious behavior for operators. This mechanism also maintains a reasonably sized set of operators, ensuring high system activity under the "1-of-n honest node" assumption.

2. Accelerated Dispute Resolution

By adopting a multi-round challenger rotation mechanism, the challenge processing cycle has been greatly shortened, effectively reducing the finality time to less than 1 day.

3. Incentive-Aligned Challenge Economy

Successful challengers can receive a "fraud bounty" consisting of the stake from malicious proposers. This mechanism increases the participation rate of challenges and aligns the economic incentives between challenging behavior and the risk of operator misconduct.

General Operator Model: Integrated Reconstruction of Economics and Architecture

To achieve the above mechanism, the GOAT Network integrates and reconstructs the complex separation of roles in BitVM2.

In the traditional BitVM2 architecture, the Rollup system includes various roles, such as Sequencer, Challenger, Operator, and Committee members. Due to the significant differences in responsibilities and costs among these roles, designing a fair and efficient Rollup economic model and incentive mechanism has become a highly challenging task.

The core innovation of the GOAT Network lies in unifying these roles into a single identity - Universal Operator (referred to as Operator), and through a role rotation mechanism, allowing all participants to take on different responsibilities in turn at different times. All Operators are required to stake in L2, and each round will be assigned to a specific role, bringing the following four major advantages:

• Revenue and Cost Balance: The GOAT network ensures a relative balance between income and expenditure in the long term by rotating operators between profitable roles and high-cost roles, avoiding the situation where some operators bear high computational costs for extended periods.
• Incentive mechanism alignment: The cross-subsidy mechanism between different roles smooths income fluctuations and incentivizes operators to maintain honest participation in any role.
• Lowering the participation threshold: Small and medium nodes do not need to continuously bear high-cost roles, and can easily participate, enhancing the system's decentralization and openness.
• Enhance system resilience: Even if individual operators go offline, the system can maintain operation through flexible role allocation, avoiding dependence on a single point.

In summary, the GOAT Network unifies roles such as sorters, calculators, and challengers into a role pool composed of staker operators, with all operators taking turns to assume responsibilities and being subject to a penalty mechanism. Proposers who submit fraudulent states will be punished, and challengers who fail to perform their duties or maliciously challenge will also face penalties. This mechanism ensures that honest behavior is economically optimal while preventing the long-term concentration of roles in specific individuals through a clear rotation mechanism, thus reducing the risks of centralization.

Overview of Protocol Architecture: A Systemic Closed Loop Built Around General Operators

This architecture must not only cover the cross-chain in and out processes of assets (Bridge-In & Bridge-Out), but also achieve trusted submission of the sorter set, on-chain coordination of the challenge process, and efficient generation and verification of zk proofs. The following are the core components of the GOAT BitVM2 protocol architecture:

Universal Operator Model

In GOAT BitVM2, each general operator runs the same software and stakes BTC for participation eligibility. Through deterministic rotation or a random mechanism based on stake weight, these operators take turns performing the following roles: Sequencer (responsible for block production), Prover (generating zkSNARK proofs), Publisher (submitting state data to L1), and Challenger (to dispute fraudulent states). Each operator will experience roles that are both profitable and incur costs, thus avoiding role concentration and enhancing the system's fault tolerance through diversity.

Deposit and Withdrawal Process (Bridge-in and Bridge-out)

• Deposit: Users lock BTC and obtain PegBTC on L2.
• Withdrawal/Peg-out: There is no need to rely on L1 to verify the complex BitVM2 withdrawal script. Instead, GOAT uses an atomic swap mechanism to complete the withdrawal process directly with the operator, while incorporating anti-fraud protocols to ensure safety and reliability.

Sequencer Set Commitment

• The operator submits the Merkle Root of their public key set via the OP_RETURN of the Bitcoin main chain.
• L2 utilizes the Transaction Introspection feature to verify the historical BTC status and match it with the set of orderers on L1. This design does not require modifications to the Bitcoin consensus rules while achieving strong alignment with the native BTC state.

Efficient Dispute Resolution and zkMIPS Performance Enhancement

For the native zkRollup of Bitcoin to be viable, it must have an efficient fraud detection and dispute resolution system. GOAT BitVM2 has made the following designs in terms of challenge model and proof performance:

Multi-Round Random Challenger Selection

When a challenger is needed (for example, during the operator reimbursement process), the system will randomly select a challenger from all staked nodes. If the selected challenger does not timely initiate a challenge, the system will randomly select a new challenger as a substitute. If the new challenger successfully identifies fraud and initiates a challenge, all previous challengers who failed to perform their duties will be penalized (their stakes will be forfeited). It is worth noting that anyone can initiate a challenge in any round, thus maintaining the security of the "1-of-n honest participants" assumption.

In addition, the random role assignment and fully penalizable staking mechanism effectively prevent behaviors such as bribery attacks, system ransom-style extortion, and malicious interference (griefing).

On-Chain and Off-Chain Execution

Most of the computational logic (such as ZKP generation, fraud verification, BitVM2 interactive scripts, etc.) is executed on L2, with only the final results (state submission, challenge processing, penalty operations, etc.) uploaded to L1. This design significantly reduces on-chain gas costs while ensuring the verifiability of the entire system.

ZKP performance improvement: self-developed zkMIPS

GOAT's self-developed zkMIPS is a zkVM compatible with the MIPS instruction set, optimized for STARK/SNARK backends. By batch processing multiple blocks and generating a unified proof periodically (e.g., every hour), GOAT's prover achieves high cost efficiency. In challenges, the "truth-table" method of BitVM2 can be used to locate disputed positions, thereby quickly resolving disputes.

Summary

Compared to the original BitVM2: faster, more stable, more practical

GOAT BitVM2 uses the Bitcoin network as the settlement layer and builds a decentralized sequencer network as the computing layer. Under the assumption of "1-of-n honest participants", the scheme successfully solves key problems in BitVM2 such as flexible amount withdrawals and insufficient challenger incentives. To speed up optimistic verification, GOAT has introduced a multi-round challenge mechanism to greatly improve the efficiency and effectiveness of fraud detection. In addition, combined with zkMIPS' ability to efficiently generate ZK proofs, GOAT BitVM2 has become the most secure and performant zkRollup protocol in the current Bitcoin ecosystem, which is expected to significantly accelerate the actual implementation of BitVM2 in the market.

Not only has the GOAT BitVM2 made breakthroughs in its technical architecture, but it has also built a powerful economic system based on generalized operator rotation. This system ensures that responsibilities such as sorter, prover, challenger, and publisher are fairly distributed among all stakers. Through transaction fee sharing, fraud bounties, and penalty mechanisms, the protocol encourages honest behavior while economically penalizing malicious actions, thereby creating a sustainable, fair, and resilient decentralized ecosystem.

GOAT BitVM2, as the first truly implemented Bitcoin zkRollup protocol, has achieved:

• Native security and compatibility without hard forks
• Rapid Challenge Mechanism
• Economic Incentive Reconstruction
• Efficient Zero-Knowledge Proof Engine
• BitVM2 moves from theoretical models to engineering practice

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