# MedChain: Efficient Healthcare Data Sharing via Blockchain
###### Abstract  
Healthcare information exchange is an important research topic, which can benefit both healthcare providers and patients. In healthcare data sharing, many cloud-based solutions have been proposed, but the trustworthiness of a third-party cloud service is questionable. Recently, blockchain has been introduced in healthcare record sharing, which does not rely on trusting a third party. However, existing approaches only focus on the records collected from medical examination. They are not efficient in sharing data streams continuously generated from sensors and other monitoring devices. Today, IoT devices have been widely deployed and sensors and mobile applications can monitor patients' body conditions. The collected data are shared to laboratories and institutions for diagnosis and further study. Moreover, existing approaches are too rigid to efficiently support metadata change. In this paper, an efficient data-sharing scheme is proposed, called MedChain, which combines blockchain, digest chain, and structured P2P network techniques to overcome the above efficiency issues in the existing approaches for sharing both types of healthcare data. Based on MedChain, a session-based healthcare data-sharing scheme is devised, which brings flexibility in data sharing. The evaluation results show that MedChain can achieve higher efficiency and satisfy the security requirements in data sharing. blockchain; healthcare data; electronic health record; data stream; healthcare information exchange; data sharing; peer-to-peer; decentralization; digest chain +
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the market evidence has shown the potential of the blockchain-based solutions from both a profit shift (Figure 1a) and management awareness (Figure 1b). However, there are still some challenges in healthcare blockchain adoption. Within the major technical barriers, efficiency (including scalability and latency) is one of the top concerns (Figure 1a,d). Existing blockchain-based solutions are less efficient in sharing data streams from Internet-of-Things (IoT) devices. First, the data from IoT devices are time-series data streams, such as ECG signals. In storage, they are cut into many data chunks. Different from a single healthcare record, accessing a data stream requires access to all the data chunks. Existing schemes are designed to verify the integrity for a single record. For verifying a data stream, they need to download the digest of each chunk and check the integrity for all of them, which is inefficient, especially for accessing a long stream. Second, the description of data could be changed from time to time. For example, a new tag or category could be added to the existing data. Managing mutable information on blockchain either needs to add new blocks, which consumes more storage space, or needs to re-write the entire blockchain. Moreover, data sharing is a dynamic process. When a sharing is over, some temporary information, such as the location of the actual data and the cryptographic keys used for security purpose, needs to be cleared, which prevents them from littering the storage space. Existing schemes are incapable of providing such a mechanism, since the information stored on blockchain is immutable. When IoT is applied in healthcare, it can be expected that more data will be shared and storage space overhead will become an outstanding problem. Thus, efficiently sharing healthcare data has become an emergent problem. To solve the problem, a new healthcare data sharing solution called MedChain, is proposed, which introduces the following novelties. First, it leverages two separate decentralized networks: a blockchain network and a peer-to-peer (P2P) storage network. The blockchain network stores the fingerprint of data, session, and operation, such as data digest, which are immutable, while the P2P  
Figure 1: The potential of blockchain-based solution and major external barriers of adoption in the healthcare industry: (**a**) Healthcare investment in blockchain by 2018 [9].