# Healthchain: A Privacy Protection System for Medical Data Based on Blockchain
## 1 Introduction  
With the widespread application of information technology in the medical field, there is a surge in the amount of medical data being produced. Because there is a large amount of such data, which itself has diverse data structures, collecting and analyzing these data and exploring their potential value can effectively promote the progress of clinical medicine and drug research and development [1]. Alternatively, in order to record and track the patient's condition more efficiently, and to facilitate patient referrals, many medical institutions have jointly established shared databases to store data, such as electronic medical records. However, while this increases the convenience of electronic medical treatment and helps with the analysis of medical data (which promotes the development of medical research), privacy disclosure problems exposed by medical data sharing are becoming more and more obvious. For example, in an analysis of thousands of online medical service systems around the world, Greenbone Networks found that more than 24 million patient data records could be easily accessed or downloaded from the network [2]. In addition, more than 1.19 billion medical images are transmitted on the network due to an improper configuration of the picture archiving and communication system (PACS). These data contain a large number of personal privacy information, such as name, date of birth, attending physician, diagnostic information, etc. For some particular diseases (such as AIDS), the disclosure of such information could seriously damage personal reputations. Worse, attackers will be able to analyze and use this information to commit fraud (e.g., using an ID card number to impersonate a patient's identity), extortion, or to tamper with this information. Therefore, the interests of many institutions and individuals are in conflictwith such technologies because of privacy concerns. Obviously, these problems have become a major obstacle to the comprehensive popularization of electronic medical systems. Therefore, the design of a medical data-sharing solution which is able to protect patient privacy as much as possible in the life cycle of medical data, and in the future for data analysis, is particularly important. It should be noted that due to the variety of types and sources of medical data, this paper mainly explores the protection of various clinical data and derived data generated by patients in the process of treatment in the hospital, such as personal identity information, medical institution information, electronic medical record data, and medical insurance information. In addition, in the whole life cycle of medical data (data acquisition, data storage, data sharing, and data analysis), this paper mainly solves the problem of the privacy protection of data in the storage and sharing stages. This paper shows how we can use blockchain and mainstream cryptography technology to provide a relatively safe and efficient solution for medical data sharing between medical institutions within a certain range. It is worth mentioning that, because there is no absolutely secure encryption method, we try to consider the issue of privacy protection using another way of thinking, that is, by dividing the data and using different methods to hide it. In so doing, the sensitivity of the data is greatly reduced. Only authorized personnel can obtain the complete data. Otherwise, even if a certain part of the data is cracked, the attacker can only obtain the incomplete data, and the privacy can still be better protected. This is a major innovation outlined in this article.