###### Abstract  
This work presents an efficient and effective system allowing hospitals to share patients' private information while ensuring that each hospital database's medical records will not be leaked; moreover, the privacy of patients who access the data will also be protected. We assume that the thread model of the hospital's security is semi-honest (i.e., curious but honest), and each hospital hired a trusted medical records department administrator to manage patients' private information from other hospitals. With the help of Homomorphic Encryption- and Private Set Intersection - related algorithms, our proposed system protects patient privacy, allows physicians to obtain patient information across hospitals, and prevents threats such as troublesome insider attacks and man-in-the-middle attacks. p _algorithms_ Article  
A Privacy-Preserving Symptoms  
Aid of Homomorphic Encryption and Private Set Intersection Schemes  
20231062023  
patient side: When a patient wants to retrieve his past medical records from a hospital, the patient needs to justify his identification (e.g., providing his ID number) to the hospital to verify the patient's legitimate identity. Although examining the ID allows the hospital to complete her system-level identification, the patient may not want to be identified by the hospital if data retrieving is his only objective. For example, discovering from the hospital's past records and knowing there is a medical dispute with the hospital may infringe on the patient's privacy and, more seriously, the patient's rights and interests in treatment. In addition to regulatory limitations, it may also be against the institution's interests to disclose the relevant medical records of patients receiving medical services there. Nevertheless, adequate and complete records of patient visits are necessary for medical institutions to provide optimal patient care. To meet the conflicting needs of both sides, we propose a system that allows patients to retrieve or even consult their past medical records stored in other hospitals to help doctors make a precise diagnosis. The system is operated under the guidance of the Hospital's electronic medical records system (EMRS) administrator and the corresponding patient's consent. To safeguard privacy, other institutions should not know which patients' past medical records have been retrieved except the current medical institution the patient is visiting. This system relieves the patient's burden of remembering or possessing all medical histories while maintaining patient privacy. It also allows doctors to provide the best medical services with adequate patient medical records. Notice that, with the aid of Homomorphic Encryption algorithms, our proposed system provides an end-to-end secure secret exchanging capability and can operate directly between hospitals. In other words, except for those who must be legally involved, there is no need to acquire assistance from another third party. In addition, to overcome the substantial computational load and memory space usage brought by the Homomorphic Encryption schemes, we enhanced a series of existing acceleration mechanisms to improve the system's usability vastly. So, it can be treated as an effective and efficient system for accessing or sharing private information among medical institutions. We justify our claim through experiments with system parameters at a practice scale.