To make data hacking infeasible
Approaches
Encryption
Data is split in parts and kept separately so that hacker will not have any use if he can access one part
To enforce data privacy
Approaches
Secure search. A method to search without decryption of data
https://www.sciencepubco.com/index.php/ijet/article/view/15519
https://www.cossacklabs.com/blog/secure-search-over-encrypted-data-acra-se.html