Researchers in SRI’s Computer Science Laboratory developed the theory of non-interference, one of the most influential theoretical approaches to the study of computer security.
The theory provides a formal foundation for the specification and analysis of security policies and the mechanisms that enforce them. The idea of noninterference is relatively simple: a security domain is noninterfering with another domain if no action performed by the security domain can influence subsequent outputs seen by the other domain.
Noninterference has been quite successful in providing formal underpinnings for military multilevel security policies and for the methods of verifying their implementations.