Paper 2025/1985

OUF: Oblivious Universal Function with domain specific optimizations

Abstract

The growing need for secure computation has spurred interest in cryptographic techniques that operate on encrypted data without revealing its content. Fully Homomorphic Encryption (FHE), especially LWE-based schemes, enables such processing while preserving confidentiality. Decentralized computing offers scalable resources without requiring in-house servers, but it relies heavily on the confidentiality guarantees of underlying schemes. While many existing protocols successfully protect input privacy, function confidentiality remains a largely overlooked but crucial aspect of secure delegated computation. In this work, we present a novel Oblivious Universal Function (OUF) scheme that enables a client to outsource computation of an arbitrary function to an untrusted server while hiding both the input data and the function being applied. Our construction leverages LWE-based FHE and a virtual-tape evaluation model to support composable, non-interactive, and reusable function execution. Crucially, the server remains oblivious not only to the encrypted inputs but also to the structure, type, and identity of the function it is executing. OUF thus bridges the gap between theoretical privacy guarantees and practical secure computation in decentralized environments.