Privacy-Preserving Forward and Backward Contact Tracing in Body Area Networks Using Blockchain

Preventing the outbreak of any pandemic like Covid-19 is a challenging task. Contact tracing is a technique where all the people who have come in close proximity of a given person is found. Contact tracing is classified into two types: forward contact tracing and backward contact tracing. Forward contact tracing finds all the people who have come in touch with a specific Covid positive person after a specific time. Backward contact tracing finds all the people who had come in touch with the specific Covid positive person before a specific time. Forward contact tracing helps to find the users who are at high risk of getting infected. Backward contact tracing helps to find asymptotic infected person who in turn had come in touch with several other persons who needs to be traced. Backward contact tracing also helps to identify asymptotic super-spreader who has caused several new infections. We have proposed a privacy preserving forward and backward contact tracing scheme for body area network (BAN) users using blockchain. Here, the inter-BAN communications are recorded in the form of adjacency matrix which is a suitable data structure for contact tracing. The blocks that contain the all the encrypted interban communication records, in the blockchain, within a given time window, are retrieved by the miner and the necessary tuples in the adjacency matrices in the blocks are returned to the trusted authority. Trusted authority decrypts the adjacency matrix row elements and returns the valid user ids to the public administration. Security of the proposed scheme has been analyzed against common attacks and verified using AVISPA tool. Simulation based computational overhead of the BAN users has also been reported.