Leveraging Blockchain for Immutable Logging and Querying Across Multiple\n Sites

Blockchain has emerged as a decentralized and distributed framework that\nenables tamper-resilience and, thus, practical immutability for stored data.\nThis immutability property is important in scenarios where auditability is\ndesired, such as in maintaining access logs for sensitive healthcare and\nbiomedical data.However, the underlying data structure of blockchain, by\ndefault, does not provide capabilities to efficiently query the stored data. In\nthis investigation, we show that it is possible to efficiently run complex\naudit queries over the access log data stored on blockchains by using\nadditional key-value stores. This paper specifically reports on the approach we\ndesigned for the blockchain track of iDASH Privacy & Security Workshop 2018\ncompetition.Particularly, we implemented our solution and compared its loading\nand query-response performance with SQLite, a commonly used relational\ndatabase, using the data provided by the iDASH 2018 organizers. Depending on\nthe query type and the data size, the run time difference between blockchain\nbased query-response and SQLite based query-response ranged from 0.2 seconds to\n6 seconds. A deeper inspection revealed that range queries were the bottleneck\nof our solution which, nevertheless, scales up linearly. Concretely, this\ninvestigation demonstrates that blockchain-based systems can provide reasonable\nquery-response times to complex queries even if they only use simple key-value\nstores to manage their data. Consequently, we show that blockchains may be\nuseful for maintaining data with auditability and immutability requirements\nacross multiple sites.\n