The invention relates to a system for processing data that can be exchanged between at least a first domain having a security level A and a second domain having a security level B, A being different from B, characterized in that it comprises at least one elementary entity EEi including a routing module URi and a device UTi for processing data, the routing module URi including at least one input Ii into the domain having the A security level for the data to be processed, and at least one first output Pi for the data that has not been processed and remains in the domain with the A security level, and a second output Li connected to the processing device UTi for the data processed and transferred into the domain with the B security level via the output Oi.