Practical Quantum Cryptography: A Comprehensive Analysis (Part One)

TL;DR

This paper provides a comprehensive analysis of practical quantum cryptography systems in real-world environments, including new formulas, detailed loss and cost calculations, protocol generalizations, and a high-speed photon detection design.

Contribution

It introduces explicit formulas for secrecy capacity, detailed loss and cost analyses, and a novel high-speed photon detection method for practical quantum cryptography.

Findings

Universal expressions for secrecy capacity and rate derived.

Detailed loss and cost calculations for fiber and satellite systems.

Proposed high-speed photon detection method for improved throughput.

Abstract

We perform a comprehensive analysis of practical quantum cryptography (QC) systems implemented in actual physical environments via either free-space or fiber-optic cable quantum channels for ground-ground, ground-satellite, air-satellite and satellite-satellite links. (1) We obtain universal expressions for the effective secrecy capacity and rate for QC systems taking into account three important attacks on individual quantum bits, including explicit closed-form expressions for the requisite amount of privacy amplification. Our analysis also includes the explicit calculation in detail of the total cost in bits of continuous authentication, thereby obtaining new results for actual ciphers of finite length. (2) We perform for the first time a detailed, explicit analysis of all systems losses due to propagation, errors, noise, etc. as appropriate to both optical fiber cable- and satellite communications-based implementations of QC. (3) We calculate for the first time all system load costs associated to classical communication and computational constraints that are ancillary to, but essential for carrying out, the pure QC protocol itself. (4) We introduce an extended family of generalizations of the Bennett-Brassard (BB84) QC protocol that equally provide unconditional secrecy but allow for the possibility of optimizing throughput rates against specific cryptanalytic attacks. (5) We obtain universal predictions for maximal rates that can be achieved with practical system designs under realistic environmental conditions. (6) We propose a specific QC system design that includes the use of a novel method of high-speed photon detection that may be able to achieve very high throughput rates for actual implementations in realistic environments.