Attacks on unsecured systems result in important loses. Many of the causes are related to non-conformance of system architecture and implementation to the requirements. To reduce these conformity problems, Model Driven Engineering proposes using modelling languages for defining requirements and architecture and model transformations between them. We therefore introduce a modelling language extension/ profile for defining system requirements with basic security requirement concepts. We also formalize the model transformation between this profile and a security formal verification method. We exemplify our approach on a medical case study.