The ping-pong protocol with a prior privacy amplification

A modified version of the well known ping-pong protocol is proposed and analyzed in the paper. The operation of the improved version exploits inevitable errors introduced by the eavesdropping in the message mode a feature which has not been exploited so far. A proposed protocol improvement is in its role similar to the privacy amplification known from the quantum key distribution schemes, but no randomization of transferred information is introduced and deterministic character of communication is preserved. Messages are processed in blocks which guarantees that an eavesdropper is faced with a computationally infeasible problem as long as the system parameters are within reasonable limits. Information processing does not require quantum memory registers and confidential communication is possible without prior key agreement or some shared secret.