  Noninterference provides a control over information flow in a system for
ensuring confidentiality and integrity properties. In the literature this
notion has been well studied as transitive noninterference and intransitive
noninterference. In this paper we define a framework on the notion of
conditional noninterference, which allows to specify information flow policies
based on the semantics of action channels. Our new policies subsume the
policies of both transitive and intransitive noninterference, and support
dynamic requirements such as upgrading and downgrading. We also present
unwinding relations that are both sound and complete for the new policies.
