Electronic health records (EHRs: digital collections of patient health status and diagnosis) are generally shared, analyzed and stored on cloud servers. One operational challenge is to ensure that EHRs are stored correctly, for example using provable data possession (PDP). Seeking to contribute to the literature, we propose a certificateless PDP scheme for cloud-based EHRs. In our scheme, we distribute multiple copies of EHRs on different cloud servers to allow for corrupted EHRs to be recoverable from other intact copies. The scheme is also designed to resist copy-summation attack which assures that cloud servers are storing EHRs honestly. In our approach, EHRs are stored in ciphertext form so that only authorized users can decrypt and gain access to the information. We also design a new data structure – map version marker table (MVMT) – for block-level dynamic operations and data traceability. Specifically, MVMT allows an authorized doctor to access historical EHRs to inform their diagnosis and decision-making. The security and performance analyses show that our scheme is secure (assuming the intractability of the computational Diffie-Hellman problem) and is practical to support cloud-based EHR applications.

Provable data possession (PDP) is widely considered to be an efficient method in verifying the integrity of remote data. While earlier PDP schemes are generally designed to check the integrity of data copies on a single cloud server (CS), there have been attempts to design multicopy and multiserver PDP (MCMS-PDP) schemes in recent years. However, it is known that MCMS-PDP schemes may be vulnerable to copy-summation attacks or do not support dynamic operations. The former enables a (dishonest) CS to only store a summation of copies for successful verification, while the latter does not allow the data owner to update the stored data. In this article, we propose a new MCMS-PDP scheme based on homomorphic verifiable tags. Specifically, our proposed scheme is designed to check the integrity of all copies in one challenge–response and resist copy-summation attacks. The scheme also supports public verification and block-level dynamic operations, such as modification, insertion, and deletion using the divide-and-conquer table. We then prove the security of our scheme, assuming the intractability of the computational Diffie–Hellman problem, in the random oracle model. We also evaluate the performance of the scheme to demonstrate its efficiency.