AModel for Multilevel Security Based on Operator Nets

A security model for the SNet multilevel secure distributed system, bawd on a behavioral semantics for operator nets and expressed in Lucid, is described. This model subsumes a previously published model of the network within SNet and includes authorized downgrading as well as the security policies enforced by trusted hosts connected to the network. The previous model is based on seven rather ad hoc constraints without presenting a coherent argument regarding security. The model described in this paper provides a more general abstract model than is provided by those´ seven constraints.