P-1935-J-Conc-Biblio
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5.0 Conclusions The intent of this document has been: (1) to provide a comprehensive overview of the important properties of traditional capability-based systems, (2) to point out the advantages and deficiencies of such systems with regard to the NCSC [TCSEC83] requirements, (3) to outline some possible approaches for the elimination of such deficiencies, and (4) to compare the properties of such systems to those of descriptor-based systems (with which the computer security community has been somewhat more familiar). Thus, this document can be used as a background document by both evaluators and designers of capability-based systems. 'In both cases, the reader should make use of the references provided in this document in order to help him understand some of its more subtle conclusions. [For the readers with special research and/or development interests in this area, an extensive bibliography is also provided as an appendix to this paper.] The research work necessary for this paper has led to the following findings. First, the notion of a "traditional" capability-based system can be defined based on a set of properties which are common to many capability-based systems. These properties are found in the areas of capability-based addressing and protection, and they support a number of general security and integrity policies. The discussion of the set of common properties has been essential to the investigation of the TCSEC impact on traditional capability systems. Without such a defmition, the impact and corresponding analysis would be questionable at best, because no general conclusions could be drawn from individual case studies. Second, traditional capability-based systems prevent the implementation of security policy and accountability as required by the TCSEC, and make some aspects of trusted facility management and recovery more difficult than those of other systems. However, tl}ereare extensions (to what is defmed as traditional capability-based systems) that have been proposed for, and implemented in, experimental systems which allow the support of security policies and accountability mechanisms similar to those of TCSEC. All such extensions are well within the limits of present-day technology. This suggests that one cannot rule out a priori a system based on capabilities from environments where the requirements of the TCSEC are important. Careful analysis of such systems must be performed to determine that the problems presented above have indeed been solved. Third, there are advantages and disadvantages of capability-based systems in comparison with descriptor-based systems. Such a comparison is important to the understanding of the fundamental and technological advantages and disadvantages of traditional capability-based systems. The results of such a comparison are easily derived from the discussion of the previous sections. Descriptor-based systems are superior to traditional capability-based systems in support of DoD policies and accountability. Traditional capability-based systems appear superior to descriptor-based systems from the point of view of support for operating system architecture and stnicturing because of their support for protection domains. However, one must note that the additional mechanisms for the support of protection domains in descriptor-based systems are well within the present-day technology. Similarly, extensions to traditional capability systems are possible to alleviate some of their fundamental problems with discretionary and mandatory policy, and with audit. 71 References Almes78 Almes, G. and G. 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