A fully homomorphic encryption (FHE) scheme allows a client to encrypt and delegate its data to a server that performs computation on the encrypted data that the client can then decrypt. While FHE gives confidentiality to clients' data, it does not protect the server's input and computation. Nevertheless, FHE schemes are still helpful in building delegation protocols that reduce communication complexity, as the ciphertext's size is independent of the size of the computation performed on them. We can further extend FHE by a property called circuit privacy, which guarantees that the result of computing on ciphertexts reveals no information on the computed function and the inputs of the server. Thereby, circuit private FHE gives rise to round optimal and communication efficient secure two-party computation protocols. Unfortunately, despite significant efforts and much work put into the efficiency and practical implementations of FHE schemes, very little has been done to provide useful and practical FHE supporting circuit privacy. In this work, we address this gap and design the first randomized bootstrapping algorithm whose single invocation sanitizes a ciphertext and, consequently, serves as a tool to provide circuit privacy. We give an extensive analysis, propose parameters, and provide a C++ implementation of our scheme. Our bootstrapping can sanitize a ciphertext to achieve circuit privacy at an 80-bit statistical security level in between 1.3 and 0.9 seconds, depending which Gaussian sampling algorithm is used, and whether the parameter set targets a fast Fourier or a number theoretic transform-based implementation. In addition, we can perform non-sanitized bootstrapping in around 0.27 or 0.14 seconds. Crucially, we do not need to increase the parameters to perform computation before or after sanitization takes place. For comparison's sake, we revisit the Ducas-Stehlé washing machine method. In particular, we give a tight analysis, estimate efficiency, review old, and provide new parameters.

IACR Communications in CryptologyJan 13, 20255 citations

A Comprehensive Survey on Lattice-based Cryptography and Homomorphic Encryption

Wenjie He, Jing Wang, Yuan Gao

With the popularization of cloud computing model, the outsourcing of data storage and computing services has become an indispensable trend, which lead to the related data security and privacy protection issues that have attracted extensive attention in the industry. Fully homomorphic encryption, as an encryption technology that can process ciphertext information without exposing plaintext information, has natural user data security and privacy protection characteristics. Meanwhile, the excellent quantum-resistant performance and homomorphic properties of lattice ciphers have made lattice-based homomorphic encryption schemes a much-attend research hotspot in the field of cryptography in recent years. In this paper we mainly introduce the status of all-pass encryption and several typical references for the research of lattice-based all-homomorphic cryptography.

International Academic Exchange Conference on Science and Technology Innovation (IAECST)Dec 8, 20231 citation