NTDR INFOSEC: software security and the 80486 microprocessor

This paper discusses one of the first efforts of developing a software-based secure communication system that bases security on a combination of hardware and software design features. The paper starts with an overview of the security relevant features of the 80486 architecture and draws a contrast between the protected and real mode environments of the 80486 microprocessor. In particular, protected mode features including segments, descriptor tables, gates, privilege levels and task state segments are presented as a prelude to a more detailed discussion of each feature. The value of each of these features in the development of a trusted operating environment is explored. This groundwork in place, the paper describes the application of the 80486 features to the development of security software for the Mercury NTDR (Near Term Digital Radio). The detailed description of the software architecture closes with a discussion of the role of the 80486 features in software assurance.