  Quantum cryptography allows one to distribute a secret key between two remote
parties using the fundamental principles of quantum mechanics. The well-known
established paradigm for the quantum key distribution relies on the actual
transmission of signal particle through a quantum channel. This paper shows
that the task of a secret key distribution can be accomplished even though a
particle carrying secret information is not in fact transmitted through the
quantum channel. The proposed protocols can be implemented with current
technologies and provide practical security advantages by eliminating the
possibility that an eavesdropper can directly access the entire quantum system
of each signal particle.
