International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Efficient Lattice-Based Inner-Product Functional Encryption

Tilen Marc , Faculty of Mathematics and Physics, Ljubljana, Slovenia, XLAB d.o.o., Ljubljana, Slovenia
Azam Soleimanian , DIENS, Ecole normale superieure, CNRS, PSL University, Paris, France, INRIA, Paris, France
Angshuman Karmakar , mec-COSIC, KU Leuven, Leuven, Belgium
Jose Maria Bermudo Mera , mec-COSIC, KU Leuven, Leuven, Belgium
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Presentation: Slides
Conference: PKC 2022
Abstract: In the recent years, many research lines on Functional Encryption (FE) have been suggested and studied regarding the functionality, security, or efficiency. Nevertheless, an open problem on a basic functionality, the single-input inner-product (IPFE), remains: can IPFE be instantiated based on the Ring Learning With Errors (RLWE) assumption? The RLWE assumption provides quantum-resistance security while in comparison with LWE assumption gives significant performance and compactness gains. In this paper we present the first RLWE-based IPFE scheme. We carefully choose strategies in the security proofs to optimize the size of parameters. More precisely, we develop two new results on ideal lattices. The first result is a variant of Ring-LWE, that we call multi-hint extended Ring-LWE, where some hints on the secret and the noise are given. We present a reduction from RLWE problem to this variant. The second tool is a special form of Leftover Hash Lemma (LHL) over rings, known as Ring-LHL. To demonstrate the efficiency of our scheme we provide an optimized implementation of RLWE-based IPFE scheme and show its performance on a practical use case. We further present new compilers that, combined with some existing ones, can transfer a single-input FE to its (identity-based, decentralized) multi-client variant with linear size of the ciphertext (w.r.t the number of clients).
Video from PKC 2022
  title={Efficient Lattice-Based Inner-Product Functional Encryption},
  author={Tilen Marc and Azam Soleimanian and Angshuman Karmakar and Jose Maria Bermudo Mera},