Direction de recherche : Eleni DIAMANTI

Co-encadrement : LEVERRIER Anthony, Chercheur INRIA

Continuous-variable quantum cryptographic protocols

This thesis is concerned with the study and analysis of two quantum cryptographic protocols: quantum key distribution (QKD) and unforgeable quantum money in the continuous-variable (CV) framework. The main advantage of continuous-variable protocols is that their implementation only requires standard telecommunication components. QKD allows two distant parties, Alice and Bob, to establish a secure key, even in the presence of an eavesdropper, Eve. The remarkable property of QKD is that its security can be established in the information-theoretic setting, without appealing to any computational assumptions. Proving the security of CV-QKD protocols is challenging since the protocols are described in an infinite-dimensional Fock space. One of the pressing questions in CV-QKD was establishing security for two-way QKD protocols against general attacks. We exploit the invariance of Unitary group U(n) of the protocol to establish the composable security against general attacks. We also show that active symmetrization is not required to prove security. We answer another open question in the field of CV-QKD with a discrete modulation by establishing the asymptotic security of such protocols against collective attacks. We provide a general technique to derive a lower bound on the secret key rate by formulating the problem as a semidefinite program. Quantum money exploits the no-cloning property of quantum mechanics to generate unforgeable tokens, banknotes, and credit cards. We propose a continuous-variable private-key quantum money scheme with classical verification. The motivation behind this protocol is to facilitate the process of practical implementation. Previous classical verification money schemes use single-photon detectors for verification, while our protocols require coherent detection.

Publications 2019-2021

• 2021
  • Sh. Ghorai : “Continuous-variable quantum cryptographic protocols”, soutenance de thèse, soutenance 12/02/2021, direction de recherche Diamanti, Eleni, co-encadrement : Leverrier, Anthony, Chercheur, INRIA (2021)
• 2019
  • Sh. Ghorai, Ph. Grangier, E. Diamanti, A. Leverrier : “Asymptotic security of continuous-variable quantum key distribution with a discrete modulation”, Physical Review X, vol. 9 (2), pp. 11, (American Physical Society) (2019)
  • Sh. Ghorai, E. Diamanti, A. Leverrier : “Composable security of two-way continuous-variable quantum key distribution without active symmetrization”, Physical Review A, vol. 99 (1), pp. 11, (American Physical Society) (2019)