International Association for Cryptologic Research

International Association
for Cryptologic Research

IACR News item: 19 September 2022

Tianshu Shan, Jiangxia Ge, Rui Xue
ePrint Report ePrint Report
The post-quantum security of cryptographic systems assumes that the quantum adversary only receives the classical result of computations with the secret key. Furthermore, if the adversary is able to obtain a superposition state of the result, it is unknown whether the post-quantum secure schemes still remain secure.

In this paper, we formalize one class of public-key encryption schemes, named oracle-masked schemes, relative to random oracles. For each oracle-masked scheme, we design a preimage extraction procedure and prove that it simulates the quantum decryption oracle with a certain loss. We also observe that the implementation of the preimage extraction procedure for some oracle-masked schemes does not need to take the secret key as input. This contributes to the IND-qCCA security proof of these schemes in the quantum random oracle model (QROM). As an application, we prove the IND-qCCA security of schemes obtained by the Fujisaki-Okamoto (FO) transformation and REACT transformation in the QROM, respectively.

Notably, our security reduction for FO transformation is tighter than the reduction given by Zhandry (Crypto 2019).
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