Flow Caml is an extension of the Objective Caml language with a type system tracing information flow. It automatically checks information flow within Flow Caml programs, then translates them to regular Objective Caml code that can be compiled by the ordinary compiler to produce secure programs. In this paper, we give a short overview of this system, from a practical viewpoint.

Acknowledgments I would like to thank François Pottier for his support and numerous comments in the design of the Flow Caml system and the writing of this document. An electronic version of this document is available at the following address:

Flow Caml is an extension of the Objective Caml language with a type system tracing information ow. Its purpose is basically to allow to write real programs and to automatically check that they obey some condentiality or integrity policy. In Flow Caml, standard ML types are annotated with security levels chosen in a user-denable lattice. Each annotation gives an approximation of the information that the described expression may convey. Because it has full type inference, the system veries, without requiring source code annotations, that every information ow caused by the analyzed program is legal with regard to the security policy specied by the programmer.

t, le systme vrie, sans ncessiter d'annotations du code source, que chaque ot d'information ralis par le programme analys est correct vis vis de la politique de scurit dnie par le programmeur. ######### # Caml, Analyse de ots d'information, Infrence de type, Scurit des languages de programmation ######## I An introduction to Flow Caml 7 # ######## # 1.1 Language-based Information Flow Analysis . . . . . . . . . . . . . . . . . . . . . . 9 1.2 Relating Flow Caml to Objective Caml . . . . . . . . . . . . . . . . . . . . . . . . 10 1.3 How to get the Flow Caml system ? . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.4 Theoretical background and related work . . . . . . . . . . . . . . . . . . . . . . . 10 # ######### ## 2.1 Security levels and data structures . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.1.1 Simple types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.1.2 Strings . . . . . . . . . . . . . . . . . . . . . . . . . .