Comparison analysis of stream cipher algorithms for digital communication

The broadcast nature of radio communication such as in the HF (High Frequency) spectrum exposes the transmitted information to unauthorized third parties. Confidentiality is ensured by employing cipher system. For bulk transmission of data, stream ciphers are ideal choices over block ciphers due to faster implementation speed and not introducing error propagation. The stream cipher algorithms evaluated are based on the linear feedback shift register (LFSR) with nonlinear combining function. By using a common key length and worst case conditions, the strength of several stream cipher algorithms are evaluated using statistical tests, correlation attack, linear complexity profile and nonstandard test. The best algorithm is the one that exceeds all of the tests

Implementation and integration of HF messaging system with cryptographic features

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

Performance modeling of adaptive modulation coding schemes on rayleigh fading channels

Adaptive modulation coding schemes (MCSs) are important techniques in wireless data communication to minimize the bit-error-rate (BER) and maximize throughput. Usually, the adaptive system consists a few MCSs that will intelligently adapt to channel variation. At the receiver, the MCS transition is decided by link quality analysis and the result is sent to transmitter via acknowledgement data. Therefore, the system performance cannot rely on a single MCS. This research developes a methodology to estimate an adaptive MCS performance using Markov model. The model concerns type I Hybrid automatic repeat request (ARQ) system which is a combination of forward error control (FEC) and ARQ under the Rayleigh fading condition. The two-state Markov model performance estimation (MMPE-2) and four-state Markov model performance estimation (MMPE-4) are proposed, where the system performance are estimated based on packet error probability and level crossing probability of the Rayleigh fading condition. Performance comparison between estimation models and simulation using International Radio Consultative Committee (CCIR) 520-2 channel model is made and the results shows that MMPE-4 are comparable for fade duration longer than the packet length. From the models, the analysis on traffic and acknowledgement data in term of bit BER and throughput can be done theoretically prior to any simulation and experiment. This can save a lot of time and the modification on the system can be done before proceeding for further evaluation or implementation. By using the estimation models as tools, several new adaptive MCSs are evaluated and the best adaptive system is proposed for high frequency data communication system

High Frequency spectrum: propagation, characterization, data communications and spectrum monitoring

Recent natural disasters such as the Asian tsunami in 2004 and Jogjakarta earthquake in 2005 have proven the usefulness of HF communications in relief operations. With the destruction of existing communication infrastructure, HF communications systems and infrastructure can be set be set-up and operational with minimum time and cost. Long range communications is possible by the refraction of radio waves in the ionosphere. Despite the presence of satellite and optical communications, HF communications is still important to the military, law enforcement, search and rescue, relief organizations, amateur radio, shipping and diplomatic services. Besides voice and telegraphy, data communication services available include short messaging, email and telemetry. This paper provides an overview on HF propagation, channel characterization, adaptive data communications and spectrum monitoring. Preliminary results will be presented with the direction of research that will be pursued. The research outcomes will provide a better understanding on characteristics of the HF communications channel, and solutions for effective data communications and spectrum monitoring