%0 Magazine Article %D 2020 %T Impossibility of Quantum Virtual Black-Box Obfuscation of Classical Circuits %A Gorjan Alagic %A Zvika Brakerski %A Yfke Dulek %A Christian Schaffner %X

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.

%8 5/13/2020 %G eng %U https://arxiv.org/abs/2005.06432 %0 Journal Article %J Proceedings of ASIACRYPT 2017 %D 2017 %T Quantum Fully Homomorphic Encryption With Verification %A Gorjan Alagic %A Yfke Dulek %A Christian Schaffner %A Florian Speelman %X

Fully-homomorphic encryption (FHE) enables computation on encrypted data while maintaining secrecy. Recent research has shown that such schemes exist even for quantum computation. Given the numerous applications of classical FHE (zero-knowledge proofs, secure two-party computation, obfuscation, etc.) it is reasonable to hope that quantum FHE (or QFHE) will lead to many new results in the quantum setting. However, a crucial ingredient in almost all applications of FHE is circuit verification. Classically, verification is performed by checking a transcript of the homomorphic computation. Quantumly, this strategy is impossible due to no-cloning. This leads to an important open question: can quantum computations be delegated and verified in a non-interactive manner? In this work, we answer this question in the affirmative, by constructing a scheme for QFHE with verification (vQFHE). Our scheme provides authenticated encryption, and enables arbitrary polynomial-time quantum computations without the need of interaction between client and server. Verification is almost entirely classical; for computations that start and end with classical states, it is completely classical. As a first application, we show how to construct quantum one-time programs from classical one-time programs and vQFHE.

%B Proceedings of ASIACRYPT 2017 %P 438-467 %8 2017/11/30 %G eng %U https://arxiv.org/abs/1708.09156 %R 10.1007/978-3-319-70694-8_16 %0 Conference Paper %B Computational Security of Quantum Encryption. In: Nascimento A., Barreto P. (eds) Information Theoretic Security. %D 2016 %T Computational Security of Quantum Encryption %A Gorjan Alagic %A Anne Broadbent %A Bill Fefferman %A Tommaso Gagliardoni %A Christian Schaffner %A Michael St. Jules %X

Quantum-mechanical devices have the potential to transform cryptography. Most research in this area has focused either on the information-theoretic advantages of quantum protocols or on the security of classical cryptographic schemes against quantum attacks. In this work, we initiate the study of another relevant topic: the encryption of quantum data in the computational setting. In this direction, we establish quantum versions of several fundamental classical results. First, we develop natural definitions for private-key and public-key encryption schemes for quantum data. We then define notions of semantic security and indistinguishability, and, in analogy with the classical work of Goldwasser and Micali, show that these notions are equivalent. Finally, we construct secure quantum encryption schemes from basic primitives. In particular, we show that quantum-secure one-way functions imply IND-CCA1-secure symmetric-key quantum encryption, and that quantum-secure trapdoor one-way permutations imply semantically-secure public-key quantum encryption.

%B Computational Security of Quantum Encryption. In: Nascimento A., Barreto P. (eds) Information Theoretic Security. %8 2016/11/10 %G eng %U https://link.springer.com/chapter/10.1007%2F978-3-319-49175-2_3