Security types for dynamic web data

We describe a type system for the [email protected] calculus of Gardner and Maffeis. An [email protected] is a network of locations, where each location consists of both a data tree (which contains scripts and pointers to nodes in trees at different locations) and a process, for modeling process interaction, process migration and interaction between processes and data. Our type system is based on types for locations, data and processes, expressing security levels. A tree can store data of different security level, independently from the security level of the enclosing location. The access and mobility rights of a process depend on the security level of the ''source'' location of the process itself, i.e. of the location where the process was in the initial network or where the process was created by the activation of a script. The type system enjoys type preservation under reduction (subject reduction). In consequence of subject reduction we prove the following security properties. In a well-typed [email protected], a process P whose source location is of level h can copy data of security level at most h and update data of security level less than h. Moreover, the process P can only communicate data and go to locations of security level equal or less than h.