[Resource Topic] 2021/133: smartFHE: Privacy-Preserving Smart Contracts from Fully Homomorphic Encryption

Welcome to the resource topic for 2021/133

smartFHE: Privacy-Preserving Smart Contracts from Fully Homomorphic Encryption

Authors: Ravital Solomon, Ghada Almashaqbeh


Despite the great potential and flexibility of smart contract-enabled blockchains, building privacy-preserving applications using these platforms remains an open question. Existing solutions fall short in achieving this goal since they support a limited operation set, enable private computation on inputs belonging to only one user, or even ask the users themselves to coordinate and perform the computation off-chain. To address these limitations, we propose smartFHE, a framework to support private smart contracts using fully homomorphic encryption (FHE). To the best of our knowledge, smartFHE is the first to use FHE in the blockchain model; it is also the first to allow for building arbitrary smart contracts that operate on multiple users’ inputs on-chain while preserving input/output privacy. smartFHE does not overload the user since miners are instead responsible for performing the private computation. This is achieved by employing (single and multi-key) FHE so miners can compute over encrypted data and account balances, along with efficient zero-knowledge proof systems (ZKPs) so users can prove well-formedness of their private inputs. Crucially, our framework is modular as any FHE and ZKP scheme can be used so long as they satisfy certain requirements with respect to correctness and security. We formulate a notion for a privacy-preserving smart contract (PPSC) scheme and show a concrete instantiation. We provide formal definitions along with proofs of the correctness and security of our construction. Finally, we include preliminary benchmarks to evaluate the feasibility of our instantiation.

ePrint: https://eprint.iacr.org/2021/133

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