  The rapid development of personal health records (PHR) systems enables an
individual to collect, create, store and share his PHR to authorized entities.
Health care systems within the smart city environment require a patient to
share his PRH data with a multitude of institutions' repositories located in
the cloud. The cloud computing paradigm cannot meet such a massive
transformative healthcare systems due to drawbacks including network latency,
scalability and bandwidth. Fog computing relieves the burden of conventional
cloud computing by availing intermediate fog nodes between the end users and
the remote servers. Aiming at a massive demand of PHR data within a ubiquitous
smart city, we propose a secure and fog assisted framework for PHR systems to
address security, access control and privacy concerns. Built under a fog-based
architecture, the proposed framework makes use of efficient key exchange
protocol coupled with ciphertext attribute based encryption (CP-ABE) to
guarantee confidentiality and fine-grained access control within the system
respectively. We also make use of digital signature combined with CP-ABE to
ensure the system authentication and users privacy. We provide the analysis of
the proposed framework in terms of security and performance.
