Paper 2023/628

SEC: Fast Private Boolean Circuit Evaluation from Encrypted Look-ups

Abstract

Encrypted computation has over the past thirty years, turned into one of the holy grails of modern cryptography especially with the advent of cloud computing. Modern cryptographic techniques like Fully Homomorphic Encryption (FHE) allow arbitrary Boolean circuit evaluation with encrypted inputs. However, the prohibitively high computation and storage overhead coupled with high communication bandwidth of FHE severely limit its scalability in practical applications like real-time analytics or machine learning inference. In summary, the current cryptographic literature lacks robust and scalable methods for efficient encrypted computation in practical outsourced applications. In this work, we introduce a new approach for encrypted computation called SEC (Symmetric Encryption-based Computation) which offers fast Boolean circuit evaluation with optimal storage and communication overhead while scaling smoothly to real applications. SEC relies on an efficient Searchable Symmetric Encryption (SSE) construction to leverage the power of encrypted lookups in Boolean circuit evaluation. SEC is specifically suited for client-server systems, and the server, honest-but-curious receives the client’s encrypted inputs and outputs the encrypted evaluation result while leaking only benign information to the server. SEC essentially extends the capabilities of SSE schemes from searching over encrypted databases to arbitrary function evaluation over encrypted inputs. SEC supports Boolean function composition, allowing it to evaluate complex functions efficiently without blowing up storage overhead. SEC outperforms the state-of-the-art FHE, namely, Torus FHE (TFHE) scheme with an average 103× speed-up in basic Boolean gate evaluations. We present a prototype implementation of SEC and experimentally validate its practical efficiency. Our experiments show that SEC executes arbitrary depth Boolean circuit in a single round of communication between client and server with a significant improvement in performance than the fastest TFHE backends. We exemplify the applicability of our scheme by implementing one byte AES SBox using SEC and comparing the results with TFHE.