This paper reports on a method to handle the verification of various security properties of imperative source code embedded on smart cards. The idea is to combine two program verification approaches: the functional verification at the source code level and the verification of high level properties on a formal model built from the program and its specification. The method presented uses the Caduceus tool, built on top of the Why tool. Caduceus enables the verification of an annotated C program and provides a validation process that we used to generate a high level formal model of the C source code. This method is illustrated by an example extracted from the verification of a smart card embedded operating system.