2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/90566We demonstrate that secure communication using coherent states is possible. The optimal eavesdropping strategy for an M-ry ciphering scheme shows that the minimum probability of error in a measurement for bit determination can be made arbitrarily close to the pure guessing value P_e=1/2. This ciphering scheme can be optically amplified without degrading the security level. New avenues are open to secure communications at high speeds in fiber-optic or free-space channels.2 1/2 pages, 1 figure, Proceedings of the Sixth International Conference on Quantum Communication, Measurement and Computing Proceedings (QCMC'02), July 2002Quantum Physicstext