## CryptoDB

### Paper: A New Simple Technique to Bootstrap Various Lattice Zero-Knowledge Proofs to QROM Secure NIZKs

Authors: Shuichi Katsumata , AIST, Japan DOI: 10.1007/978-3-030-84245-1_20 (login may be required) Search ePrint Search Google CRYPTO 2021 Many of the recent advanced lattice-based Sigma-/public-coin honest verifier (HVZK) interactive protocols based on the techniques developed by Lyubashevsky (Asiacrypt'09, Eurocrypt'12) can be transformed into a non-interactive zero-knowledge (NIZK) proof in the random oracle model (ROM) using the Fiat-Shamir transform. Unfortunately, although they are known to be secure in the __classical__ ROM, existing proof techniques are incapable of proving them secure in the __quantum__ ROM (QROM). Alternatively, while we could instead rely on the Unruh transform (Eurocrypt'15), the resulting QROM secure NIZK will incur a large overhead compared to the underlying interactive protocol. In this paper, we present a new simple semi-generic transform that compiles many existing lattice-based Sigma-/public-coin HVZK interactive protocols into QROM secure NIZKs. Our transform builds on a new primitive called __extractable linear homomorphic commitment__ protocol. The resulting NIZK has several appealing features: it is not only a proof of knowledge but also straight-line extractable; the proof overhead is smaller compared to the Unruh transform; it enjoys a relatively small reduction loss; and it requires minimal background on quantum computation. To illustrate the generality of our technique, we show how to transform the recent Bootle et al.'s 5-round protocol with an exact sound proof (Crypto'19) into a QROM secure NIZK by increasing the proof size by a factor of 2.6. This compares favorably to the Unruh transform that requires a factor of more than 50.
##### BibTeX
@inproceedings{crypto-2021-31108,
title={A New Simple Technique to Bootstrap Various Lattice Zero-Knowledge Proofs to QROM Secure NIZKs},
publisher={Springer-Verlag},
doi={10.1007/978-3-030-84245-1_20},
author={Shuichi Katsumata},
year=2021
}