Design and assessment of lightweight cryptographic algorithms on ESP32 and STM32 for IoD security

Securing communications in autonomous drones is vital for protecting sensitive navigation and positioning data under tight hardware constraints. This study focuses on implementing the lightweight encryption algorithms Speck and Simon on ESP32 microcontrollers. Additionally, the Simon64/128 algorithm was tested on three STM32 platforms (F1, F4, and L4), selected for their frequent use in autonomous drones. The study evaluates encryption times on these platforms using optimized code versions, complemented by a comparative evaluation of STM32 platforms, profiling execution time and instruction-cycle efficiency, and identifying the optimal hardware security trade-offs for drone applications. We performed an SMT based cryptanalysis of reduced round Simon64/128 by encoding its round function and key schedule as bit vector constraints, recovering the ten most probable keys per configuration and illustrating how security degrades with fewer rounds; in particular, we show that at seven rounds the master key can be extracted in approximately 1529 s, clearly delineating the cipher security threshold. Building on these insights, we developed an SMT-guided, optimized implementation of Simon64/128 and validated its master key recovery process, quantifying the exponential increase in computational effort as the round count grows. Concurrently, our benchmarks reveal that STM32F429 reduces encryption latency by 50% compared to the F1 and L4 variants, making it the most suitable choice when balancing performance and security. These results highlight significant differences in the STM32 family, demonstrate that any reduction in the official round count must be precisely calibrated to avoid vulnerabilities, and underscore the necessity of optimizing lightweight ciphers and rigorously analyzing speed robustness trade-offs for real-time drone systems.