  The global Electronic Health Record (EHR) market is growing dramatically and
expected to reach $39.7 billions by 2022. To safe-guard security and privacy of
EHR, access control is an essential mechanism for managing EHR data. This paper
proposes a hybrid architecture to facilitate access control of EHR data by
using both blockchain and edge node. Within the architecture, a
blockchain-based controller manages identity and access control policies and
serves as a tamper-proof log of access events. In addition, off-chain edge
nodes store the EHR data and apply policies specified in Abbreviated Language
For Authorization (ALFA) to enforce attribute-based access control on EHR data
in collaboration with the blockchain-based access control logs. We evaluate the
proposed hybrid architecture by utilizing Hyperledger Composer Fabric
blockchain to measure the performance of executing smart contracts and ACL
policies in terms of transaction processing time and response time against
unauthorized data retrieval.
