Paper 2024/511

A Black-box Attack on Fixed-Unitary Quantum Encryption Schemes

Cezary Pilaszewicz, Freie Universität Berlin
Lea R. Muth, Freie Universität Berlin
Marian Margraf, Freie Universität Berlin

We show how fixed-unitary quantum encryption schemes can be attacked in a black-box setting. We use an efficient technique to invert a unitary transformation on a quantum computer to retrieve an encrypted secret quantum state $\ket{\psi}$. This attack has a success rate of 100% and can be executed in constant time. We name a vulnerable scheme and suggest how to improve it to invalidate this attack. The proposed attack highlights the importance of carefully designing quantum encryption schemes to ensure their security against quantum adversaries, even in a black-box setting.

Available format(s)
Attacks and cryptanalysis
Publication info
quantum cryptographyblack-box attackquantum cryptanalysisquantum circuits
Contact author(s)
cezary pilaszewicz @ gmail com
lea muth @ fu-berlin de
marian margraf @ fu-berlin de
2024-04-01: approved
2024-03-31: received
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      author = {Cezary Pilaszewicz and Lea R. Muth and Marian Margraf},
      title = {A Black-box Attack on Fixed-Unitary Quantum Encryption Schemes},
      howpublished = {Cryptology ePrint Archive, Paper 2024/511},
      year = {2024},
      note = {\url{}},
      url = {}
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