Impossibility of Quantum Virtual Black-Box Obfuscation of Classical Circuits

TitleImpossibility of Quantum Virtual Black-Box Obfuscation of Classical Circuits
Publication TypeMagazine Article
Year of Publication2020
AuthorsAlagic, G, Brakerski, Z, Dulek, Y, Schaffner, C
Date Published5/13/2020

Virtual black-box obfuscation is a strong cryptographic primitive: it encrypts a circuit while maintaining its full input/output functionality. A remarkable result by Barak et al. (Crypto 2001) shows that a general obfuscator that obfuscates classical circuits into classical circuits cannot exist. A promising direction that circumvents this impossibility result is to obfuscate classical circuits into quantum states, which would potentially be better capable of hiding information about the obfuscated circuit. We show that, under the assumption that learning-with-errors (LWE) is hard for quantum computers, this quantum variant of virtual black-box obfuscation of classical circuits is generally impossible. On the way, we show that under the presence of dependent classical auxiliary input, even the small class of classical point functions cannot be quantum virtual black-box obfuscated.