The design of security audit subsystems for real-time embedded avionics systems is described. The selection criteria of auditable events and the design of the audit functions are described. The data storage requirements and the data compression features of embedded avionics systems are analyzed. Two data compression algorithms applicable to avionics systems are described. Huffman encoding is optimal, but Fibonacci encoding is shown to be nearly optimal and better suited for airborne avionics systems. The memory capacity needed for audit storage is computed for typical avionics missions.
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