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Quantum cryptography in a hybrid security model

Abstract : Extending the functionality and overcoming the performance limitation of QKD requires either quantum repeaters or new security models. Investigating the latter option, we introduce the Quantum Computational Timelock (QCT) security model, assuming that computationally secure encryption may only be broken after time much longer than the coherence time of available quantum memories. These two assumptions, namely short-term computational security and noisy quantum storage, have so far already been considered in quantum cryptography, yet only disjointly. A practical lower bound on time, for which encryption is computationally secure, can be inferred from assumed long-term security of the AES256 encryption scheme (30 years) and the value of coherence time in experimental demonstrations of storage and then retrieval of optically encoded quantum information, at single-photon level range from a few nanoseconds to microseconds. Given the large gap between the upper bound on coherence time and lower bound on computational security time of an encryption scheme, the validity of the QCT security model can be assumed with a very high confidence today and also leaves a considerable margin for its validity in the future. Using the QCT security model, we propose an explicit d-dimensional key agreement protocol that we call MUB-Quantum Computational Timelock (MUB-QCT), where a bit is encoded on a qudit state using a full set of mutually unbiased bases (MUBs) and a family of pair-wise independent permutations. Security is proved by showing that upper bound on Eve's information scales as O(1=d). We show MUB-QCT offers: high resilience to error (up to 50% for large d) with fixed hardware requirements; MDI security as security is independent of channel monitoring and does not require to trust measurement devices. We also prove the security of the MUB-QCT protocol, with multiple photons per channel use, against non-adaptive attacks, in particular, proactive MUB measurement where eve measures each copy in a different MUB followed by post-measurement decoding. We prove that the MUB-QCT protocol allows secure key distribution with input states containing up to O(d) photons which implies a significant performance boost, characterized by an O(d) multiplication of key rate and a significant increase in the reachable distance. These results illustrate the power of the QCT security model to boost the performance of quantum cryptography while keeping a clear security advantage over classical cryptography.
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Submitted on : Thursday, April 7, 2022 - 8:29:11 PM
Last modification on : Friday, April 8, 2022 - 3:06:04 AM

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  • HAL Id : tel-03634698, version 1

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Nilesh Vyas. Quantum cryptography in a hybrid security model. Cryptography and Security [cs.CR]. Institut Polytechnique de Paris, 2021. English. ⟨NNT : 2021IPPAT049⟩. ⟨tel-03634698⟩

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