There is disclosed a method of communicating a long-term-secure classical message M between distant parties A and B by sharing a short-term-secure classical key K and by using a public quantum channel and a classical authenticated channel. Described developments comprise steps of sharing of a short-term-secure key K between A and B over the classical authenticated channel; encoding the classical message M at A into a quantum state, using the short-term-secure key K and sending the quantum state to B over the quantum channel; decoding reliably the message M at B, using K and the quantum state received at the output of the quantum channel. Further embodiments comprise the use of computationally-secure public-key and/or symmetric-key encryption, the use of an error correction code, the use of phase or amplitude product of coherent states at input, the use of individual (adaptative or non-adaptative) coherent receivers. System and software aspects are described.
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