CDMA-based quantum noise stream cipher for passive optical networks

The quantum noise stream cipher (QNSC) scheme, grounded in Heisenberg’s uncertainty principle, can facilitate secure communication by employing noise to obfuscate multi-base encrypted signals. The current research primarily focuses on point-to-point performance, while studies on point-to-multipoint schemes remain limited due to compatibility issues with multiple access technologies. This study presents a QNSC scheme for passive optical networks based on code-division multiple access (CDMA). In our scheme, different user datasets are combined into one dataset via CDMA and then encrypted using the QNSC protocol. Each user can recover their corresponding dataset from the encrypted signal by employing the same security keys along with a distinct pseudo-noise code (PN code). Through simulation studies, we found that under the condition of being able to decode correctly, as the number of users increases, the optical signal-to-noise ratio (OSNR) at the receiver decreases, which leads to a gradual rise in the eavesdropper’s detection failure probability (DFP). Furthermore, the network capacity is correlated with the number of modulation bits, as the increase in modulation bits directly translates to an enhancement in the data’s carrying capability. We have conducted verification experiments, and the results confirmed that four users can acquire 64 QAM/QNSC plaintext data with an average transmission rate of 600 Mbit/s over a transmission distance of 20 km. These data were encrypted in the constellation with 64×64 symbols, achieving a DFP of up to 99.3%, and each user successfully decoded them via CDMA. We have successfully extended the fundamental point-to-point QNSC scheme to accommodate point-to-multipoint passive optical networks, establishing the foundational framework for the future large-scale deployment of quantum networks.