GECO: A Confidentiality-Preserving and High-Performance Permissioned Blockchain Framework for General Smart Contracts

Data confidentiality is essential for blockchain applications that handle sensitive data. A promising approach to achieving data confidentiality is executing smart contracts on homomorphic encrypted ciphertext and then verifying correctness through non-interactive zero-knowledge proofs (NIZKPs). However, existing solutions cannot tolerate non-deterministic (ND) contracts whose correct execution cannot be proven by NIZKPs, and suffer from poor performance for deterministic contracts due to the use of using homomorphic encryption. We present Geco, a confidentiality-preserving and highperformance permissioned blockchain framework for general smart contracts. Geco shifts part of correctness enforcement from cryptographic primitives to the blockchain layer, thereby tolerating ND contracts and maintaining verifiable correctness at the system level. To support fully homomorphic encryption (FHE) without incurring significant performance overhead, we present Стм protocol, which merges multiple conflicting transactions into a single one, thereby reducing both conflicting aborts and expensive cryptographic computations. Geco ensures strong confidentiality and supports general smart contracts. It outperforms four confidentiality-preserving blockchains by achieving up to 7.1 times higher throughput and reducing 99% tail latency down to 48.2% of the baseline.