The main slowdown of Cloud activity comes from the lack of reliable security. The on-demand security concept aims at delivering and enforcing the client’s security requirements. In this paper, we present an approach, Information Flow Past Linear Time Logic (IF-PLTL), to specify how a system can support a large range of security properties. We present in this paper how to control those information flows from lower system events. We give complete details over IF-PLTL syntax and semantics. Furthermore, that logic enables to formalize a large set of security policies. Our approach is exemplified with the Chinese Wall commercial-related policy. Finally, we discuss the extension of IF-PLTL with dynamic relabeling to encompass more realistic situations through the dynamic domains isolation policy.