2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/91249The methods of quantum cryptography enable one to have perfectly secure communication lines, whereby the laws of quantum physics protect the privacy of the data exchanged. Each quantum-cryptography scheme has its own security criteria that need to be met in a practical implementation. We find, however, that the generally accepted criteria are flawed for a whole class of such schemes.3 pages, 1 color figure; this is a brief announcement of a recent result, about which a more detailed report is being preparedQuantum Physicstext