## 1 Introduction  
A healthcare information system allows patients and other users to login remotely to medical services to access health data through the Internet. To protect the privacy of patients and ensure security over the public network, secure communication is necessary. Rapid technological development has made access to information part of our daily life, along with health care. In the field of personal health care, data sharing has become an important topic. The security of data in transmission is attracting increasing attention. In recent years, blockchain technology has also been attracting more attention. Relevant research has been published at a high rate [1, 2, 3, 4]. It draws on many fields, including medicine, leasehold, energy, and others. However, with respect to personal information privacy, most attempts to satisfy security-related regulations use modular and exponential calculation. To improve the security of the healthcare system, many studies have proposed the use of blockchain technology. In 2016, [PERSON] et al. [1] proposed a method of using blockchain technology to decentralize the management of large-scale data in electronic medical records (EMR), and enable patients to access them. The use of blockchain technology makes the records immutable and prevents malicious tampering with user cases, which violates the rights of patients. In the same year, [PERSON] et al. [5] proposed a scheme in which blockchain technology is used to share data among hospitals. Using the concept of a distributed ledger and fast healthcare interoperability resources (FHIR), they established standards for the integration of patient data with different specifications at different hospitals. They used Merkle tree architecture to integrate each user's medical records, facilitating verification of the data. In 2018, [PERSON] et al. [6] proposed BlocHIE, a blockchain-based platform for healthcare information exchange, which uses two loosely coupled blockchains to handle different kinds of healthcare data: the EMR-Chain handles electronic medical records while the PHD-Chain handles personal healthcare data. Implementation and evaluation revealed the practicability and effectiveness of BlocHIE. In 2018, [PERSON] et al. [7] proposed a medical information preservation system that is based on blockchain. The system splits each private file into many parts and uses elliptic curve cryptography to generate a key to encrypt the file for access by the patient. The file is then stored in different storage spaces in the system, and the file storage location index value is encrypted. However, this method was inconsistent with blockchain's decentralization. Also in 2018, [PERSON] et al. [8] proposed an architecture of blockchain that ensures decentralization all healthcare data on centralized servers. They proposed a blockchain-based platform that can store and manage huge healthcare datasets with ease and security. In the same year, [PERSON] et al. [9] observed a significant shift of healthcare data to cloud services, but the mechanisms of this shift may not ensure data security and privacy. [PERSON] et al. [10] proposed a unique blockchain-based method for accessing patient information that cannot be communicated but can be stored securely on wearable devices using blockchain. The patient's information is stored using an encrypted private key and a public key. The private key can be decrypted only using the patient's biometric signature. The combination of the public and private keys ensures that the critical records of the patient can be accessed only in emergency situations. As seen above, a lot of research on healthcare information systems that use blockchain technology has been published [11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. However, to achieve the mutual authentication, the confidentiality and non-repudiation of data, and other security specifications, most research relies on computationally heavy modular exponential operations or elliptic curve point multiplication operations.