Abstract: A system comprising: at least one training unit for one or more data owners collaborating to the system for storing private data and at least one encrypted model, said training unit being implemented as a trusted execution environment; at least one aggregator unit for each model owner collaborating to the system for storing and executing code of a training algorithm, said aggregator unit being implemented as a trusted execution environment; at least one administration unit for controlling communication and synchronization between the at least one training unit and the at least one aggregator unit, said administration unit being implemented as a trusted execution environment; wherein the communication between the at least one training unit and the at least one aggregator unit is encrypted.