Improving key rates of the unbalanced phase-encoded BB84 protocol using the flag-state squashing model

Abstract

All phase-encoded BB84 implementations have signal states with unbalanced amplitudes in practice. Thus, the original security analyses a priori do not apply to them. Previous security proofs use signal tagging of multi-photon pulses to recover the behaviour of regular BB84. This is overly conservative, as for unbalanced signals, the photon-number splitting attack does not leak full information to Eve. In this work, we exploit the flag-state squashing model to preserve some parts of the multi-photon generated private information in our analysis. Using a numerical proof technique, we obtain significantly higher key rates compared with previously published results in the low-loss regime. It turns out that the usual scenario of untrusted dark counts runs into conceptual difficulties in some parameter regime. Thus, we discuss the trusted dark count scenario in this paper as well. We also report a gain in key rates when part of the total loss is known to be induced by a trusted device. We highlight that all these key rate improvements can be achieved without modification of the experimental setup.

arXiv comment17 pages, 6 figures

References in corpus (19)

• The Security of Practical Quantum Key Distribution
• Decoy State Quantum Key Distribution
• Quantum Key Distribution with High Loss: Toward Global Secure Communication
• Beating the PNS attack in practical quantum cryptography
• Security Aspects of Practical Quantum Cryptography
• Distillation of secret key and entanglement from quantum states
• General Entanglement Breaking Channels
• Quantum key distribution over 122 km of standard telecom fiber
• Post-selection technique for quantum channels with applications to quantum cryptography
• Entanglement as precondition for secure quantum key distribution
• Symmetry implies independence
• Unconditional Security of Practical Quantum Key Distribution
• Unambiguous state discrimination in quantum cryptography with weak coherent states
• Numerical approach for unstructured quantum key distribution
• Squashing Models for Optical Measurements in Quantum Communication
• Reliable numerical key rates for quantum key distribution
• Asymptotic security analysis of discrete-modulated continuous-variable quantum key distribution
• Squashing model for detectors and applications to quantum key distribution protocols
• Security proof of the unbalanced phase-encoded BB84 protocol

Cited by in corpus (8)

• Dimension Reduction in Quantum Key Distribution for Continuous- and Discrete-Variable Protocols
• Robust Interior Point Method for Quantum Key Distribution Rate Computation
• Imperfect Phase-Randomisation and Generalised Decoy-State Quantum Key Distribution
• Postselection technique for optical Quantum Key Distribution with improved de Finetti reductions
• Using Cascade in Quantum Key Distribution
• Improved Decoy-state and Flag-state Squashing Methods
• Finite-size analysis of prepare-and-measure and decoy-state QKD via entropy accumulation
• Imperfect detectors for adversarial tasks with applications to quantum key distribution