A Flexible Authorization Architecture for Systems of Interoperable Medical Devices

Robust authentication and authorization are vital to next-generation distributed medical systems - the Medical Internet of Things (MIoT). However, there is yet no good authorization model for real-time multi-channel data from systems of heterogeneous devices providing multiple physiological parameters for clinicians who may change on a minute-by-minute basis. We present a flexible authorization architecture for interoperable medical systems, and an implementation and evaluation in the context of the Medical Device Coordination Framework (MDCF) high-assurance middleware. Our framework is based on the well-studied Attributed Based Access Control model, but we introduce a new method of attribute inheritance that provides more fine-grained access control, supporting multiple different authorization levels for multiple physiological data channels from the same device, and rich and expressive policy specification which facilitates plug-and-play connectivity of devices - most do not require pre-specification of individual permissions. Our architecture is standards-compliant and modular, using the eXtensible Access Control Markup Language (XACML), and Axiomatics Language for Authorization (ALFA) for policy specification, and standalone authorization modules which can be integrated with other platforms such as OpenICE. We stress-test our implementation in a realistic distributed system configuration, and show that the unoptimized system introduces negligible network and storage overhead, and minimal memory and CPU overhead.