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Numerous projects have launched in the past year, called themselves Bitcoin Layer 2 networks. Many of those projects have failed to gain traction with users, or make meaningful, verifiable progress toward inheriting native Bitcoin security.

To understand the challenges of successfully launching a Bitcoin Layer 2 network, let’s first define what we mean.

A Bitcoin Layer 2 network is a technical solution designed to improve the transaction speed of Bitcoin. By moving some transactions off-chain from the Bitcoin main chain, a Bitcoin L2 reduces the burden on the main chain, enhancing transaction processing speed and reducing transaction costs. Common Layer 2 network technologies include Lightning Network, State Channels, and the popular BitVM2 bridge solution combined with zkRollup.

Challenges Faced by Bitcoin Layer 2 zkRollup Solutions

- Security: Security is the most critical factor for Bitcoin holders. Security needs to address network consistency, liveness, and resilience. 

Consistency, or consensus security, ensures the immutability of the entire network’s ledger. 

Liveness ensures the overall network’s availability.

Resilience ensures the network can quickly recover from attacks or abnormalities. 

To ensure Bitcoin mainnet security inheritance, a Bitcoin zkRollup Layer 2 network must fully commit to the transactions on Layer 2, with commitments verifiable directly by Bitcoin miners. However, the difficulty lies in the current Bitcoin script's inability to implement Covenant. Recently, promising solutions have emerged, including BitVM2, function encryption, and the latest ColliderScript protocol. 

Another challenge is maintaining the liveness and resilience of Layer 2 networks. Many zkRollups face centralization issues due to centralized sequencers, leading to high centralization within the Rollup chain and a lack of sufficient incentives for other players to participate, forming a vicious cycle.

- Programmability: Programmability is the infrastructure for BTCFi. 

Bitcoin, the largest asset in the blockchain ecosystem, has long been seen as a store of value. However, it lacks practical applications and revenue generation opportunities due to its scalability limitations and the inherent restrictions of its scripting language, making it difficult to support complex decentralized finance (DeFi) applications. 

For Bitcoin holders, earning returns from their BTC typically requires depositing assets in centralized exchanges or using bridging services to convert BTC into wrapped tokens (such as wBTC). However, these methods introduce additional risks, such as trust risks with centralized platforms, which contradict Bitcoin's decentralized nature. Drawing from the experience of the rich DeFi ecosystem under ETH, introducing EVM compatibility becomes very important.

GOAT Network: Bitcoin Layer 2 Network with EVM Compatibility Based on zkMIPS

GOAT Network is the first Bitcoin Layer 2 network to enhance security using zkMIPS, BitVM2, and decentralized sequencers. It achieves 100% EVM compatibility and ensures Bitcoin network security with just a 1-of-n assumption. The core highlights of GOAT Network include:

• True Decentralization: Through the groundbreaking permissionless decentralized sequencer protocol, all cross-chain messages, including asset peg-ins, peg-outs, and Layer 2 network state rollups, can achieve consensus on both Bitcoin and GOAT Network. This completely eliminates reliance on a single centralized entity, ensuring true decentralization. This innovation significantly simplifies the trust setup of the BitVM2 protocol while providing equivalent security guarantees.
• Full Bitcoin Verification without Forking: GOAT Network combines decentralized sequencers with the BitVM2 protocol, making the BitVM2 protocol practical by allowing Bitcoin scripts to directly verify proofs, thus inheriting Bitcoin’s native security. zkMIPS serves as the scalability infrastructure for GOAT, enabling 100% EVM compatibility and significantly accelerating proof generation and verification, bringing unprecedented ecosystem scalability to GOAT.
• Dual Punishment Mechanism Ensures Security: GOAT Network introduces a "dual punishment" mechanism in Bitcoin Layer 2, combining Bitcoin's native penalty mechanism with the GOAT consensus layer penalty system. This effectively reduces the probability of dishonest behavior in the GOAT Rollup protocol. The mechanism specifically targets risks such as double signing, node downtime, and malicious reimbursement attacks from Sequencer nodes, significantly enhancing network security and reliability.

This technological breakthrough marks the beginning of a new era of decentralized Bitcoin Layer 2 networks, setting a new industry standard for blockchain technology’s future.

In the integration of zkMIPS with BitVM2, zkMIPS not only optimizes the Groth16 proof speed; it also optimizes the verification stage in various ways, such as using hints to reduce the complexity of Bitcoin script's Miller loop calculation, segmenting the verifier circuit for commitments, compressing zkVM public input commitments, and leveraging decentralized sequencers to ensure that the public input and superblock are on the same fork. This reduces the complexity of the BitVM2 optimistic challenge process to some extent.

zkMIPS: The First Zero-Knowledge Virtual Machine (zkVM) Based on the MIPS Instruction Set

zkMIPS is the first zkVM based on the MIPS instruction set. The MIPS instruction set is a mature instruction set with several advantages:

1. MIPS32r2’s instructions are richer than RISCV32IM, with J/JAL series instructions offering jump lengths up to 256 MiB, making it easy to implement jumps in statically linked scenarios. MIPS32r2 also has rich bit manipulation instructions that are absent in RISCV32IM, which require the B extension. MIPS32r2 features MOVN/MOVZ condition selection instructions that can replace jump instructions in many cases, improving performance and reducing instruction count. It also has integer multiply-accumulate instructions, enhancing performance and reducing instruction numbers. MIPS32r2 includes SEH and SEB symbol extension instructions that easily handle sign extension for char and short data types.
2. MIPS32r2’s instructions have been in use for over 20 years, ensuring robust integration without module interconnection issues or potential disputes over copyrights. Extensions to MIPS might have integration issues, but MIPS as an instruction set is a well-established and mature system. The MIPS instruction manual provides clear and detailed descriptions of instruction behavior. MIPS has been successfully used in blockchain applications, such as the Optimism fraud proof verification, which is based on a MIPS VM.

zkMIPS is fully functional and allows developers to prove any program written in widely used high-level languages such as Rust and Golang. It provides a suite of developer-friendly tools, including ZKM Playground, ZKM-Project-Template, and ZKM Proof Network, which help developers build their ZKP products with a low barrier to entry.

zkMIPS helps developers in ensuring the safety of circuit logic. Developers can use familiar languages to implement any application without needing to audit the zero-knowledge proof circuits. Unlike traditional ZKP development, zkMIPS strictly adheres to the MIPS32r2 instruction set, meaning that if developers have already audited their application’s business logic, there's no need to audit the circuit again.

ZKM provides a proof network that helps developers and projects quickly generate proofs and supports horizontal scaling, enabling real-time proof generation. This allows developers and projects to build their decentralized Web3 applications with high efficiency. Additionally, zkMIPS supports precompiles and other proof acceleration solutions.

zkMIPS supports various innovative zkVM use cases (including Bitcoin L2 for GOAT Network), promoting widespread adoption of zkVM technology across sectors such as zkLLM and zkIdentity.

As the first zkVM based on the MIPS instruction set, zkMIPS combines MIPS' mature ecosystem with ZKM’s ZKP infrastructure, and will significantly accelerate the deployment of zkVM.