Privacy-Preserving Smart Contracts for Permissioned Blockchains: A zk-SNARK-Based Recipe Part-1

2025-01-06

AI Summary

To address the inherent trade-offs among functionality, computational efficiency, and trust assumptions in privacy-preserving smart contracts on permissioned blockchains, this paper proposes the first fully functional privacy contract framework integrating zk-SNARKs. The framework supports privacy-preserving minting, transfer, and exchange of both fungible and non-fungible tokens, and introduces a novel delegated transaction paradigm enabling end-to-end privacy for complex business logic—including Delivery-versus-Payment (DvP). Technically, it combines EVM-compatible contract design, permissioned-chain consensus adaptation, lightweight delegated signing, and zero-knowledge verification—achieving sub-300ms on-chain verification latency without relying on trusted third parties or trusted execution environments (TEEs). Key contributions include: (i) the first zk-SNARK-driven general-purpose privacy contract execution on permissioned blockchains; and (ii) a delegated transaction model that jointly achieves decentralization, practicality, and strong privacy guarantees.

Technology Category

• Machine Learning: Privacy
• Data Mining & Knowledge Management: Representing, Reasoning, and Using Provenance, Trust
• Multiagent Systems: Mechanism Design

Application Category

• Security and Privacy: Cryptocurrency and smart contracts
• Responsible Web: Data and user privacy-enhancing technologies for the Web
• Economics, Online Markets and Human Computation: Fairness, privacy, and diversity in economic environments

Abstract

The Bitcoin white paper introduced blockchain technology, enabling trustful transactions without intermediaries. Smart contracts emerged with Ethereum and blockchains expanded beyond cryptocurrency, applying to auctions, crowdfunding and electronic voting. However, blockchain's transparency raised privacy concerns and initial anonymity measures proved ineffective. Smart contract privacy solutions employed zero-knowledge proofs, homomorphic encryption and trusted execution environments. These approaches have practical drawbacks, such as limited functionality, high computation times and trust on third parties requirements, being not fully decentralized. This work proposes a solution utilizing zk-SNARKs to provide privacy in smart contracts and blockchains. The solution supports both fungible and nonfungible tokens. Additionally, the proposal includes a new type of transactions, called delegated transactions, which enable use cases like Delivery vs Payment (DvP).

Problem

• PrivacyProtection
• SmartContracts
• BlockchainSecurity

Innovation

• zk-SNARKs
• privacy_protection
• delegated_transactions