Zk-SNARK Marketplace with Proof of Useful Work

TL;DR

The paper tackles the energy waste inherent in traditional PoW by introducing a PoUW protocol where the useful work is the generation of zk-SNARK proofs. It presents a consensus design that integrates SNARK generation, forming a decentralized marketplace for proof computation at the consensus layer and ensuring PoW-like properties are preserved. Key contributions include the network roles, a layered block proposer lottery with mechanisms to reduce wasted work (including bucketing and chained proofs), a circuit registry subnetwork, and an initial extension to handle private inputs via Witness Obfuscating Outsourcing. The work demonstrates, through modeling and discussion, that SNARK generation can secure the chain while producing verifiable, useful cryptographic proofs, with practical considerations for proof time, scalability, and privacy that open avenues for real-world deployment and further privacy-preserving extensions.

Abstract

Proof of Work (PoW) is widely regarded as the most secure permissionless blockchain consensus protocol. However, its reliance on computationally intensive yet externally useless puzzles results in excessive electric energy wasting. To alleviate this, Proof of Useful Work (PoUW) has been explored as an alternative to secure blockchain platforms while also producing real-world value. Despite this promise, existing PoUW proposals often fail to embed the integrity of the chain and identity of the miner into the puzzle solutions, not meeting necessary requirements for PoW and thus rendering them vulnerable. In this work, we propose a PoUW consensus protocol that computes client-outsourced zk-SNARKs proofs as a byproduct, which are at the same time used to secure the consensus protocol. We further leverage this mechanism to design a decentralized marketplace for outsourcing zk-SNARK proof generation, which is, to the best of our knowledge, the first such marketplace operating at the consensus layer, while meeting all necessary properties of PoW.

Figures (12)

• Figure 1: Diagram illustrating the lifecycle of a single block, including the different roles of users within the protocol.
• Figure 2: The lottery mechanism during block mining (as described in \ref{['sec:lottery']}). A lottery is performed every time a new proof is added to the block in progress.
• Figure 3: The overlap probability $P_{overlap}(m,t)$ of two randomly selected transaction sets of size $t$ from the mempool of size $m$.
• Figure 4: Sycomore ledger creates a split in the block DAG in times of high traffic. Transactions here are color-coded based on their prefix, which determined their position after a split. Adapted from sycomore.
• Figure 5: Stochastic Time Colored Petri Net (STCPN) modeling the consensus protocol with two miners and a single bucket. The network can be extended to more miners or buckets by replicating the miner or bucket component.