A method for enhancing the security of a quantum key distribution (QKD) system having QKD stations Alice and Bob (10) is disclosed. The method includes encrypting key bits generated by a random number generator and sent to a polarization or phase modulator to encode weak optical pulses as qubits to be shared between Alice and Bob (10). Key bit encryption is achieved by using shared password and a stream cipher. Bob obtains at least a subset of the original key bits used by Alice (10) by utilizing the same cipher stream and the shared password.
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