We propose a modified version of the Bennett–Brassard 1984 quantum key distribution protocol intended to tolerate losses, certain forms of noise, and the so-called photon number splitting attack. These are the issues facing the realization of practical quantum key distribution. The modified protocol is based on quantum non-demolition measure ments for systems using weak coherent pulses. Our scheme ensures that emissions cor responding to zero photon pulses, multi-photon pulses, and detector double-clicks are dis carded before sifting to improve sifting efficiency and increase the secret key rate. More over, we perform the finite key analysis to obtain the maximal achievable secret-key frac tion and the corresponding optimal number of signals. Also, we compare our proposed protocol to the decoy-state quantum key distribution protocol. We observe that our pro posed quantum key distribution scheme enables a more extended transmission distance than the decoy-state quantum key distribution protocol. Thus, this an advance in quantum communication because current limitations on quantum key distribution involve transmit ting secret keys over more considerable distances in the presence of noise or losses in optical fibres