Deterministic quantum-public-key encryption: forward search attack and randomization

TL;DR

This paper demonstrates that deterministic quantum-public-key encryption schemes are vulnerable to forward search attacks, but introducing randomness can effectively prevent such attacks in the quantum setting.

Contribution

It establishes the vulnerability of deterministic quantum-public-key encryption to forward search attacks and proposes a method to convert them into secure randomized schemes.

Findings

Deterministic quantum-public-key encryption schemes are susceptible to forward search attacks.

Randomization can be used to secure quantum-public-key encryption against such attacks.

The approach applies to any deterministic quantum-public-key bit-encryption scheme.

Abstract

In the classical setting, public-key encryption requires randomness in order to be secure against a forward search attack, whereby an adversary compares the encryption of a guess of the secret message with that of the actual secret message. We show that this is also true in the information-theoretic setting -- where the public keys are quantum systems -- by defining and giving an example of a forward search attack for any deterministic quantum-public-key bit-encryption scheme. However, unlike in the classical setting, we show that any such deterministic scheme can be used as a black box to build a randomized bit-encryption scheme that is no longer susceptible to this attack.