How to control, initializate and communicate a STM32L4 with STPM4RasPi

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Hi,

I have a custom made board using a STM32L4 and I want to add some security to the data. So my flow diagram is: sensors get data-> data goes to L4-> L4 inicializates RasPi and passes the sensor data -> RasPi send back seured data to L4

Is this something easy achivable? any reference guide or functions for implementing this? any example on how to interact between this devices?

Thanks a lot in advanced