Sisu: A Decentralized Trustless Bridge for Ethereum Full Node Verification

Core Concepts

Sisu protocol presents a detailed approach and implementation to efficiently prove Ethereum full node using recursive SNARK, distributed general GKR, and Groth16. The protocol addresses the challenges of proving Ethereum full node, including validating public keys under previous beacon state and ensuring pairwise distinct public keys, without requiring worker-to-worker communication.

Abstract

The Sisu protocol is designed to provide a decentralized trustless bridge for Ethereum full node verification. The key highlights and insights are:

Sisu introduces an algorithm to prove that the majority (more than 2/3) of validators in an Ethereum epoch are valid under the previous beacon state and are all pairwise distinct. This allows Sisu to replace the RANDAO algorithm in Ethereum consensus.

Sisu proposes a new approach that requires no worker-to-worker communication and minimal traffic between worker and master, enabling better scalability compared to previous designs like zkBridge.

Sisu uses a distributed general GKR system with a new type of "accumulation gate" to reduce the number of layers and gates in the circuit, achieving a 3-4x speed-up compared to a layered circuit.

Sisu incorporates GPU hardware acceleration with multiple optimization strategies, first implementing on CPU and gradually porting to GPU for the parallelizable parts.

Sisu is designed towards decentralized proving, making a trade-off of increased constraints for better decentralization, which aligns with the emerging distributed prover market model.

Stats

The Ethereum mainnet has about one million validator nodes at the time of writing.
Each Ethereum block has around 32,000 validators producing 32,000 signatures.
Proving the validity of one Ethereum block requires verifying the aggregation of 32,000 signatures, ensuring each signature belongs to an active validator under the previous beacon state, and validating the RANDAO algorithm for selecting validators.
Proving the RANDAO algorithm for 32,000 validators requires an estimated 100 billion to 1 trillion gates, exceeding the computational capacity of current proving systems.

Quotes

"To prove that one block is valid with regard to current beacon state, here is a list of necessary but not exhaustive tasks a prover needs to prove: 1) All these 32,000's signatures should be aggregated (in different committees) and valid under the new block hash. 2) Each of these signatures belongs to an active validator under the previous beacon state. 3) Each validator index must abide by an RANDAO algorithm which randomly shuffles and selects a set of validators for each epoch."
"The challenge of proving Ethereum full node is generating proof for 32,000 nodes. The second and third tasks require proving multiple SHA256 hashes. To prove the second task for one validator, a prover needs to show that the validator's public key is part of a Merkle path whose root is the previous beacon state hash. Ethereum consensus uses SHA256 for hashing and the current best SHA256 proof requires about 27,000 constraints. Each path length from validator info leaf to the root is between 50 and 60. We are looking at 1,350,000 constraints per Merkle path per validator. Multiplying this number by 32,000 yields 43.2 billion constraints."

Key Insights Distilled From

Sisu: Decentralized Trustless Bridge For Full Ethereum Node

by Billy Pham,H... at arxiv.org 04-17-2024

https://arxiv.org/pdf/2404.10404.pdf

Deeper Inquiries

How can Sisu's approach be extended to support other blockchain networks beyond Ethereum

Sisu's approach can be extended to support other blockchain networks beyond Ethereum by adapting the protocol to the specific consensus mechanisms and structures of those networks. Since Sisu focuses on proving the validity of a full Ethereum node using zero-knowledge proofs, a similar approach can be applied to other blockchains with smart contract capabilities.
To support other blockchain networks, the following steps can be taken:

Understanding the Consensus Mechanism: Analyze the consensus algorithm of the target blockchain to determine the requirements for proving node validity.
Adapting the Circuit Design: Modify the circuit design to accommodate the specific data structures and operations of the new blockchain network.
Implementing Network-specific Features: Incorporate features unique to the target blockchain, such as different hashing algorithms or consensus rules.
Testing and Validation: Thoroughly test the adapted protocol on the new blockchain network to ensure compatibility and security.

By following these steps and customizing the Sisu protocol to fit the requirements of different blockchain networks, Sisu's approach can be successfully extended to support a variety of platforms beyond Ethereum.

What are the potential security implications of replacing Ethereum's RANDAO algorithm with Sisu's validator uniqueness proof, and how can this be further analyzed and mitigated

Replacing Ethereum's RANDAO algorithm with Sisu's validator uniqueness proof introduces potential security implications that need to be carefully analyzed and mitigated. The RANDAO algorithm is a crucial component of Ethereum's consensus mechanism, and any changes to it must be thoroughly evaluated to ensure the security and integrity of the network.
Security Implications:

Risk of Sybil Attacks: Without the RANDAO algorithm, malicious actors may attempt to manipulate the validator selection process by creating multiple fake identities.
Increased Centralization: Depending on how the uniqueness proof is implemented, there could be a risk of centralization if certain validators have an advantage in the selection process.
Validation Accuracy: Ensuring that the uniqueness proof accurately identifies and verifies validators is essential to prevent fraudulent activities.

Mitigation Strategies:

Comprehensive Testing: Conduct extensive testing and simulations to evaluate the effectiveness and security of the uniqueness proof mechanism.
Peer Review: Engage with security experts and the blockchain community to review the proposed changes and provide feedback on potential vulnerabilities.
Continuous Monitoring: Implement monitoring tools to detect any anomalies or suspicious behavior in the validator selection process.
Fallback Mechanism: Have a contingency plan in place to revert to the original RANDAO algorithm if any security issues arise.

By conducting thorough security assessments, implementing robust mitigation strategies, and involving the community in the evaluation process, the potential security implications of replacing Ethereum's RANDAO algorithm with Sisu's validator uniqueness proof can be analyzed and mitigated effectively.

Given the focus on decentralization, how can Sisu's design be adapted to incentivize a diverse set of prover participants and ensure fairness in the distributed prover market

To adapt Sisu's design to incentivize a diverse set of prover participants and ensure fairness in the distributed prover market, the following strategies can be implemented:

Incentive Mechanisms: Implement reward systems such as token incentives or transaction fees for prover participants based on their contribution to the network.

Random Selection: Use a random selection process to assign tasks to prover participants, ensuring equal opportunities for all participants to engage in the network.

Proof of Contribution: Introduce a mechanism where prover participants are rewarded based on their level of contribution to the network, encouraging active participation and fairness.

Community Governance: Establish a governance model where participants have a say in decision-making processes, promoting transparency and inclusivity in the network.

Diverse Participation: Encourage participation from a diverse range of individuals and organizations to prevent centralization and promote decentralization in the prover market.

Fair Competition: Ensure that all prover participants have equal access to resources and opportunities within the network, fostering a competitive yet fair environment.

By incorporating these strategies into Sisu's design, the protocol can incentivize diverse participation and ensure fairness in the distributed prover market, ultimately enhancing the decentralization and security of the network.