Concise and Tight Security Analysis of the Bennett-Brassard 1984 Protocol with Finite Key Lengths

TL;DR

This paper provides a precise security analysis of the BB84 quantum key distribution protocol considering finite key lengths, offering explicit procedures and bounds for practical implementation and security evaluation.

Contribution

It introduces a tight, non-approximate security bound for BB84 with finite keys and supplies explicit, practical procedures for key distillation and security assessment.

Findings

Derived tight security bounds for finite key lengths

Provided explicit procedures for key distillation and security calculation

Compared normal approximation with rigorous bounds for practical estimates

Abstract

We present a tight security analysis of the Bennett-Brassard 1984 protocol taking into account the finite size effect of key distillation, and achieving unconditional security. We begin by presenting a concise analysis utilizing the normal approximation of the hypergeometric function. Then next we show that a similarly tight bound can also be obtained by a rigorous argument without relying on any approximation. In particular, for the convenience of experimentalists who wish to evaluate the security of their QKD systems, we also give explicit procedures of our key distillation, and also show how to calculate the secret key rate and the security parameter from a given set of experimental parameters. Besides the exact values of key rates and security parameters, we also present how to obtain their rough estimates using the normal approximation.