In the multiapplicative context of smart cards, a strict con- trol of underlying information flow between applications is highly desired. In this paper we propose a model to improve information flow usability in such systems by limiting the overhead for adding information flow security to a Java Virtual Machine. We define a domain specific lan- guage for defining security policies describing the allowed information flow inside the card. The applications are certified at loading time with respect to information flow security policies. We illustrate our approach on the LoyaltyCard, a multiapplicative smart card involving four loyalty applications sharing fidelity points.