MulShare: A Multi-Receiver Encrypted Search Scheme to Secure Cloud-Assisted EMRs Sharing

Cloud-assisted electronic medical records (EMRs) sharing has garnered significant attention in the context of smart and connected healthcare systems. However, ensuring the security of EMRs remains a critical challenge when sharing sensitive data between patients and doctors, primarily due to risks such as malicious access and information leakage. To mitigate these, recent studies leveraged searchable encryption techniques, where data senders outsource encrypted EMRs to cloud servers while allowing receivers query confidentially. Despite these efforts, existing solutions face limitations: multi-receiver search mechanisms rely on cumbersome key-sharing protocols, and their vulnerability to keyword guessing attacks (KGA), rendering them unsuitable for EMR-sharing scenarios. In this paper, we propose MulShare, a novel multi-receiver encrypted search scheme designed to address privacy preservation in cloud-assisted EMR sharing. MulShare not only enjoys efficient EMRs ciphertext sharing but also realizes medical data sender authentication. Unlike existing solutions, our design distributes distinct keys for multiple receivers and integrates a randomization mechanism into ciphertext generation. Additionally, we embed the medical sender's secret key directly into the encryption process to ensure authenticity. To validate the security guarantees, we formalize its security model and give rigorous proofs demonstrating ciphertext indistinguishability (CI security) and token indistinguishability (TI security). Comparative results indicate that our communication and computational overhead for ciphertext generation is only 13.2% to 21.1% and 5.8% to 32.1% compared to prior arts, which is effective and practical for EMRs sharing systems.