# Healthchain: A Privacy Protection System for Medical Data Based on Blockchain
## 6 Security Analysis  
In this section, we explain how our scheme meets the security requirements mentioned above:  
Anonymity: The hash value based on the patient's name and ID number is used as the unique identity of the patient, which is easy to verify, is irreversible, and which realizes the anonymity of the patient in the blockchain. At the same time, the information of medical institutions is separated from the data, which is directly reflected in the digital signature. Due to the characteristics of the group signature, only the group manager can obtain the information regarding the medical institutions from the signature. This not only protects the information of medical institutions, but also further prevents attackers from analyzing patient identity information from such information.  
Traceability: The natural traceability of blockchain and the existence of a group manager in the group signature technology enables the system to trace back to specific medical data and their signers when necessary.  
Data integrity: Blockchain technology itself has the characteristic of being tamper-proof, and each block is connected in turn. With the hash value of the block, data integrity verification can be easily carried out.  
Data confidentiality: As the mainstream symmetric encryption algorithm, the speed and security of the AES algorithm are widely recognized, while key encryption is carried out using an asymmetric encryption algorithm. It will provide good data confidentiality for the system.  
Data privacy: By anonymizing the identity and separating the information of medical institutions, only authorized personnel (such as the group manager) can obtain complete  
Figure 8: Overall system design.  
medical information, and when the transaction data is leaked, attackers cannot obtain too much valuable information (only the time and content of medical treatment in the transaction data, while there is no information about the patient and the medical institution). This greatly protects the privacy of the data.  
Resistance of birthday collision: Since the system is a consortium blockchain based on the PBFT consensus algorithm, chain transaction and block publishing rely mainly on its primary node, so it avoids the'soft-fork' of blockchain and can resist birthday collisions.  
Resistance of interception: Because each transaction is signed by the group members, and the attacker cannot modify the transaction under the premise of ensuring the validity of the signature, the system can prevent transaction interception and tampering.  
Resistance of various attacks:  
DDoS attack: Since the upload of transactions and blocks must be completed by trusted nodes, and because the size of the block and the number of transactions can be limited, the system can effectively resist DDoS attack.  
Modification attack: Due to the characteristics of group signature and blockchain, any modification of transactions by attackers will be found and rejected.  
User impersonation attack: In the consortium blockchain, only verified trusted nodes can enter the blockchain network, so the user impersonation attack is largely alleviated.