Security is gaining increasing relevance in the development of embedded devices. Towards a secure system at each level of design, this paper addresses the security aspects related to Network-on-Chip (NoC) architectures, foreseen as the communication infrastructure of next-generation embedded devices. In the context of NoC-based Multiprocessor systems, we focus on the topic, not thoroughly faced yet, of data protection. We present the architecture of a Data Protection Unit (DPU) designed for implementation within the Network Interface (NI). The DPU supports the capability to check and limit the access rights (none, read, write or both) of processors requesting access to data locations in a shared memory - in particular distinguishing between the operating roles (supervisor or user) of processing elements. We explore different alternative implementations and demonstrate how the DPU unit does not affect the network latency if the memory request has the appropriate rights. In the experim...