"In this paper, we propose HealthShare –a forwardlooking approach for secure ehealth data sharing between multiple organizations that are hosting patients’ data in different clouds. The proposed protocol is based on a Revocable Key-Policy
Attribute-Based Encryption scheme and allows users to share encrypted health records based on a policy that has been defined by the data owner (i.e. patient, a member of the hospital, etc).
Furthermore, access to a malicious or compromised user/organization can be easily revoked without the need to generate fresh encryption keys."