A TCB and security kernel architecture for supporting multi-threaded, queue-driven transaction processing applications in a multilevel secure environment is presented. Our design exploits hardware security features of the Intel 80/spl times/86 processor family. Intel's CPU architecture provides hardware with two distinct descriptor tables. We use one of these in the usual way for process isolation. For each process, the descriptor table holds the descriptors of "system-low" segments, such as code segments, used by every thread in a process. We use the second table to hold descriptors for segments known to individual threads within the process. This allocation, together with an appropriately designed scheduling policy, permits us to avoid the full cost of process creation when only switching between threads of different security classes in the same process. Where large numbers of transactions are encountered on transaction queues, this approach has benefits over traditional multilevel systems.

The reference monitor (RM) model has passed the critical test imposed by the methodology of science: it has been a productive concept for the field of computer security since its introduction. The call to abandon a productive model, however intellectually stimulating, should not be heeded simply for the sake of novelty. It is our hope that this debate will stimulate an examination of foundations, but we do not believe that such an examination, carefully undertaken, supports the affirmative case. We urge our readers and listeners to embrace the following conclusions, favoring dismissal of the resolution: first, that claims that the RM model is fundamentally flawed must be based on more than wishful thinking or technical frustration. Second, that radical claims for "new paradigms" be subjected to the usual degree of skepticism unless accompanied by compelling proofs of concept.

A multilevel database is intended to provide the security needed for database systems that contain data at a variety of classifications and serve a set of users having different clearances. A formal security model for such a system is described. The model is formulated in two layers, one corresponding to a reference monitor that enforces mandatory security, and the second an extension of the standard relational model defining multilevel relations and formalizing policies for labeling new and derived data, data consistency, and discretionary security. The model also defines application-independent properties for entity integrity, referential integrity, and polyinstantiation integrity.>

A formal security policy model that uses basic view concepts for a secure multilevel relational database system is described. The model is formulated in two layers, one corresponding to a security kernel of reference monitor that enforces mandatory security, and the other defining multilevel relations and formalizing policies for labeling new and derived data, data consistency, discretionary security, and transaction consistency. This includes the policies for sanitization, aggregation, and downgrading. The model also defines application-independent properties for entity integrity, referential integrity, and polyinstantiation integrity.>

The SeaView formal security policy model admits a range of designs for a multilevel secure relational database system. The requirement for a near-term implementation suggests that the design should utilize existing technology to the extent possible. Thus the design uses an existing database management system ported to an existing TCB (trusted computing base) environment. A preprocessor translates key constructs of the SeaView multilevel relational data model to those of the standard relational model used by the commercial database system. The underlying reference monitor enforces mandatory and basic discretionary controls with A1 assurance. By combining single-level data into a multilevel view, it is possible to use a commercial database system and classify data at the relation level to implement the SeaView model, with element-level classification.>

A multilevel relational data model that meets the basic operational requirements for a multilevel database system is described. The model is an extension of the standard relational model, and consists of multilevel relations, which contain classification attributes as well as data attributes; multilevel relational integrity rules, which extend the integrity constraints of the relational model in order to pro vide consistency for data at different access classes, including data that becomes "polyinstantiated," a decomposition method for mapping all multilevel real relations into standard (single-level) base relations; and multilevel relational operators, which perform the functions of their counterparts in the standard relational model, while also labeling derived tuples with access classes. The model is defined in terms of the standard relational model, but lends itself to a design and implementation that offers a high level of assurance for mandatory security.