One of our research areas is to create a secure, private, flexible smart contract scheme (“SPF,” hence the name “Sunscreen”). What initially started as a small(er) project to instantiate private smart contracts on Ethereum has become much more ambitious once we realized we cannot achieve our vision for a privacy-preserving smart contract (PPSC) scheme on Ethereum (at least in its current form).
What are private smart contracts?
Private smart contracts allow us to “hide” the inputs and outputs of a smart contract. They can be viewed as an extension to private transactions, allowing for a rich variety of applications to be represented in a privacy-preserving fashion—from voting to complex financial derivatives. There have been some previous proposals in the community for private smart contract schemes but they support limited computations, do not rely on provable security, or are prohibitively expensive for even (relatively) simple contracts.
What is fully homomorphic encryption?
Fully homomorphic encryption (FHE) is a privacy-preserving technology for arbitrary computation. Interest in FHE has been on the rise in both academia and industry; however, the primary focus so far has been on applications to machine learning. FHE has long been neglected in the blockchain community but recent advancements in efficient zero-knowledge proofs for lattice-based cryptography show promise. We’re excited to explore FHE’s applications to PPSCs. NuCypher’s mission is to create cryptographic infrastructure for privacy-preserving applications; we hope to accomplish this by providing individuals with a variety of choices for privacy-preserving technologies, and working in the vanguard of our field.
The Past and Future
We hope to have more exciting work to share in the coming months. For now, our past work (primarily internal documentation) can be found in our “Sunscreen” repository.
- In "Zero-Knowledge Proofs for Privacy-Preserving Smart Contracts and Transactions," I look at the main types of efficient ZKPs, some of their uses in private transaction schemes, and offers suggestions for our direction.
- In "The Future of Privacy-Preserving Smart Contracts," I outline design goals for our PPSC scheme and some cryptographic primitives such a scheme might use. This document can be viewed as the beginnings of a whitepaper.
- In "Log Proofs for RLWE Ciphertexts," Bogdan provides a prototype implementation from the paper "Short Discrete Log Proofs for FHE and Ring-LWE Ciphertexts" (by Del Pino et al.). Bogdan has previously worked on other exciting implementations in the FHE space (such as nuFHE, a GPU-accelerated FHE library).
You can also check out our talks at IEEE S&P 2020, and Devcon 2019.
Note: This is currently a separate, parallel project from our network.