Encrypted optical communication

This thesis deeply tries to analyze log-normal fading effects, which happen because of atmospheric turbulence and damages reliability, integrity, and security of data transmission in FSO systems in many ways. FSO is known to be very advantageous because of high data bit rate. Atmosphere causes signal distortions at the receiver side, performance getting worse strongly and bit error rate (BER) with packet error rate (PER) values increasing noticeably. This situation is modeled with log-normal distribution mostly. To understand these impacts, experiments divided into two stages inside this study for making more organized structure. First stage investigates unencrypted data transmission. Clear weather, fog, dust, rain environments simulated inside channel and different sigma parameters applied for every condition especially. At the receiver side threshold decision method used to recover signals later. BER and PER are calculated. This part mainly focuses on the physical layer degradation effects, turbulence how damaging signal tried to be demonstrated carefully. In second stage same system was used but data transmitted with ASCON algorithm protection applied. It is the algorithm selected by NIST standards. It provides confidentiality and performs authentication process simultaneously. Encrypted data behavior tested under different turbulence intensities additionally, weak moderate and strong fading scenarios compared step by step. Encrypted and unencrypted transmissions are evaluated carefully. ASCON high entropy ciphertext structure impact over BE performance analyzed and corrupted packet rejection ability examined strongly with many comparisons. Some differences observed after these investigations. Results clearly showing log-normal fading significantly increase error rates, FSO links becoming vulnerable under these conditions strongly. ASCON authentication mechanism continuously blocks corrupted packets acceptance. Encrypted transmissions show slightly higher BER naturally. But communication integrity preserved end-to-end. ASCON does not perform error correction actually, it only detects errors and discards invalid packets without trying to repair them. Overall, this thesis demonstrates that integrating ASCON into FSO systems improves security performance strongly. Proposed hybrid optical cryptographic structure seems promising for future communication architectures. Especially important expected for 6G based next generation networks.