Secured single stage multiphoton approach for quantum cryptography protocol in free space optic

In order to mitigate the problem of low transmission rate and limited communication distance in Quantum Communication (QCs), multiphoton over multi-stages approach has been proven to be a possible alternative to the conventional single photon approach. Multiphoton has the ability to improve the range of distances and key generation rate over multi-stages photon transmission. However, the determination of optimal mean photon numbers and number of stages in multiphoton approach remains a key challenge to make the protocols well utilized during their operations. Following this concern, three problems and their corresponding proposed solutions in this thesis are presented below: Firstly, the existing multiphoton approaches involve multiple photons to travel throughout a number of stage. Furthermore, extra time is required to update the polarization angle of optical device for encoding purposes. These conditions would result in an increase in the total transmission time of the photons to be transmitted over the quantum channel. Accordingly, a Hybrid M-Ary in Braided Single-Stage (HMBSS) approach by utilizing data compression concept is proposed to address these issues. In HMBSS, the sender is able to compress the secret message using Huffman encoding over the braided single-stage operation. This compression mechanism has reduced the number of bits required to represent a string of symbols, thereby reducing the time to encode the photons. The simulation experiments shows that HMBSS achieved promising result by 75.9% and 91.7% total average transmission time decrease as compared to the well-known Multiphoton-BSS, Multiphoton-M-ary and Multiphoton-TSIV. Secondly, providing strong authentication is the main focus in this research which aims to make multiphoton QC secure against variety types of attacks. Current authentication procedure in multiphoton QC requires public agreement to pre-share the authentication key and secret angles before onset of the transmission, therefore increasing the communication cost. As a solution, a Secure Secret Authentication Key (SSAK) is proposed. In SSAK, the quantum handshake scheme is used to share initial secret polarization angle and authentication key which is utilized before quantum communication session. The results of simulation experiments reveal that SSAK significantly outperformed the Three-stage protocol in terms of average covered angle by Eve. The simulation experiments and security analysis of initial authentication and transmission of messages verified that an eavesdropper is unable to disclose any information about the transmitted message or the authentication key. Lastly, most of the proposed QKD protocol employs a single-beam set up to transmit the photons over the free space optic which results in low bit rate and limited distance coverage due to high impact of geometrical loss. To deal with this, a transmission technique of Multiphoton Quantum Communication using multiple beam concept (MQC-MB) is proposed. Comparison is conducted in terms of total loss and received power on different number of beam shows that 4-beam is acceptable to be adapted in MQC-MB. The statistical analysis shows that such approach has reduced the total attenuation by 6dB compared to single-beam setup.

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