Implementation and integration of HF messaging system with cryptographic features

Abstract

Nowadays, with the new technology development, communication is not limited by the distances, places and time. However, the infrastructures of communication still become an issue especially in the remote places. Therefore, this project focuses on long distance communication using radio frequency spectrum. High Frequency (HF) refers to the band from 3 to 30 MHz. This radio frequency spectrum allows the communication to be made for long distances either 100 km or more, direct by sky-wave propagation. By using existing HF radio and modem, a software application was developed to allow people to exchange their digital information in the form of short messages, text files and images. This system is suitable for the people at remote areas and sea where the communication infrastructure does not exist. In order to keep information secured while transmission, the system was incorporated with cipher algorithms. The block cipher AES (Advanced Encryption Standard) is used for authentication and key distribution while the stream cipher that is based on the linear feedback shift register (LFSR) is used for confidentiality. For that purpose, several stream ciphers algorithms such as shrinking, multiplexing and memory generator were analyzed to determine their characteristics. The analysis consists; statistical test, correlation attack, linear complexity profile and guess-and-determine attack which were done to verify the strength of ciphers. From the analysis, both Self-Shrinking and W7 generator succeeded all tests but, only W7 generator is adopted into the software application. Based on field-testing on designated sites, the system is user-friendly, reliable, secured, free error transmission and operates at low power of transmission.