2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/89526An undetected eavesdropping attack must produce count rate statistics that are indistinguishable from those that would arise in the absence of such an attack. In principle this constraint should force a reduction in the amount of information available to the eavesdropper. In this paper we illustrate, by considering a particular class of eavesdropping attacks, how the general analysis of this problem may proceed.Typo in eq.(5) corrected; Figure replaced with graph for alpha=0.01; No change in final conclusionsQuantum Physicstext