US Patent 7620182 QKD with classical bit encryption

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