WHAT WE DO?
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Medical data sharing, anti-tampering, and anti-leakage have always been difficult problems in medical industry. When a patient is on referral, he or she often can not provide information on previous visits. The reason is that many hospitals in China can not share medical information in most cases, and they can only pass the easily lost paper information such as medical records and checklists to achieve part of the medical information sharing. On the other hand, the patient's medical information is easy to leak, and medical information provided in a medical dispute can not be guaranteed in terms of authenticity and impartiality. In this research, an alliance medical blockchain system based on the practical Byzantine fault tolerance algorithm (PBFT) is designed, which is a multi-node maintenance and sharing system, and is able to prevent medical data from being tampered with or leaked. This medical system can be used to solve the above medical problems. Compared with the existing medical blockchain systems, this system has some advantages and good applicability.It can be more suitable for epidemic prevention and control than traditional systems.

WHAT WE HAVE?
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From a long-term perspective of human development, the outbreak of virus epidemics in human society is likely to become a normal state, such as the previous outbreaks of SARS and MERS and the current COVID-19. In response to a large-scale epidemic, human society has not yet prepared for it. As one of the emerging technologies, blockchain should also do its best for epidemic prevention and control like 5g and artificial intelligence.

Medical information is a valuable information for patients. However, in the current medical system of hospitals in China, most of these information can not be used mutually. As a result, patients need to apply for a new medical card to record the medical information of patients every time they go to a hospital, However, paper medical records are very easy to be damaged or lost, which is a very unreliable way to record medical information. On the other hand, using traditional database to realize medical information sharing will cause further losses to patients due to unscrupulous staff members who have no professional ethics, Medical staff and patients urgently need a system that can share medical information among hospitals and ensure that patients' information will not be leaked. Blockchain is the best way to realize this system

Blockchain is a distributed database system participated by multiple independent nodes. It can store bitcoin transactions or other data safely, and ensure the security of these data or information, and prevent tampering and forgery. Blockchain is generally deployed in P2P network, which is different from the common relational database and non relational database, Blockchain uses encryption algorithms such as digital signature, hash algorithm and distributed consensus algorithm, so the stored data is extremely difficult to tamper with, destroy or erase the database operation log. Blockchain technology has the characteristics of decentralization, sequential data, collEPCive maintenance, programmability, security and credibility






According to different participants, blockchain can be divided into public chain, alliance chain and private chain. The participants of public chain can be anyone, and all those who want to participate in the maintenance of public chain can join. The blockchain serving bitcoin is a kind of public chain. Private chain refers to the internal use of an entity, The entities here can be companies, banks, hospitals, etc. at present, most of the blockchains studied by domestic banks are private chains. Alliance chain refers to a block chain composed of multiple entities and with access restrictions. Compared with public chains, alliance chain can not be joined if you want to join, but you need to get certain permission to enter, Compared with private chain, alliance chain differs from private chain in that it participates in many different companies or groups. These entities jointly maintain the blockchain and share the information in the blockchain.

The entities in the medical blockchain are hospitals and medical institutions. The administrative and financial aspEPCs of these entities are completely independent, and they are different entities. At the same time, these entities are supervised and managed by the government, and have strict access and grading system, and have certain access restrictions. Medical data is not only the personal privacy of a patient, but also involves state secrets, According to the above characteristics, medical blockchain is actually a kind of alliance chain

At present, most medical blockchain systems use pox series consensus algorithm to reach distributed consensus. Blockchain consensus algorithm refers to the algorithm to reach distributed consensus in the blockchain system, that is, the blockchain system detEPCs the legitiEPCy of data and adds blocks to the blockchain system. Currently, pox series algorithms mainly have proof of work, The problem to be solved by the blockchain consensus algorithm is the Byzantine general problem . The reason why the problem is difficult to solve is that there may be multiple proposals in the system at any time (because the cost of the proposal is very low), and the final consistency confirmation needs to be completed, The process is very difficult. The pox series algorithm is to reach a consensus by increasing the proposal cost and relaxing the demand for final consensus confirmation. POW algorithm is generally applied to the public chain, requiring more nodes and larger computing power to maintain . The process of generating blocks by POS algorithm depends on the digital currency held by the node, Dpos algorithm requires the holders of digital currency to sel EPC a certain number (generally 101) of block producers, and re elEPC the block generators every other period of time . They do not meet the needs of medical blockchain, that is, they do not need large amount of computing power maintenance, and do not need the generation of elEPCronic currency, In this paper, we first use the practical Byzantine fault tolerance (pbft) to construct a medical chain that can run with fewer nodes and does not need a lot of computing power to maintain.