Personal Health Record (PHR) is an emerging patient-centric model of health information exchange, which is often outsourced to be stored at third party, such as cloud. To assure the patients control over access to their own PHRs, However, by storing PHRs in the cloud, the patients lose physical control to their personal health data, which makes it necessary for each patient to encrypt her PHR data before uploading to the cloud servers. Under encryption, it is challenging to achieve fine-grained access control to PHR data in a scalable and efficient way using Hierarchical Attribute Based Encryption. For each patient, the phr data should be encrypted so that it is scalable with the number of users having access. Also, since there are multiple owners (patients) in a PHR system and every owner would encrypt her PHR files using a different set of cryptographic keys, it is important to reduce the key distribution complexity in such multi-owner settings. © 2017 Elsevier B.V., All rights reserved.