Blockchain-Based Multi-keyword Search on Encrypted COVID-19 Contact Tracing Data.

Contact tracing data contain highly sensitive information in which any form of leakage will significantly threaten the security and privacy of the individual. Encryption schemes can be used to ensure confidentiality; however, the usability of the retrieval system will be reduced considerably as the encrypted data does not support searchability. Hence, searchable encryption could be applied to contact tracing data. This paper introduces our implementation of a blockchain-based multi-keyword searchable encryption for COVID-19 contact tracing data. We used Advanced Encryption Standard as the symmetric primitive for encrypting datasets and Attribute-based Encryption as the asymmetric primitive for encrypting the search index. We incorporated Blockchain-based storage into our scheme to assure the integrity of the datasets and search index. It provides immutable storage and ensures data integrity and non-repudiation, as any form of access will be logged automatically. The results show that the scheme works efficiently without compromising any security goals. Compared to the existing searchable contact tracing schemes, it provides more features and maintains efficiency even if a large search index was used within the system.