Data storage server and client devices for securely storing data

A method for operating a client device, wherein the method comprises:

• determining whether data to be stored in a database of a data storage server comprises security sensitive data to be stored in an encrypted data structure of one or more encrypted data structures of the database;
• in response to determining that the data to be stored in the database comprises security sensitive data, encrypting the security sensitive data with an encryption key;
• and
• providing the data, including the encrypted security sensitive data, and an identifier of the encryption key to the data storage server for storing, based on the identifier of the encryption key, the security sensitive data in the encrypted data structure of the one or more encrypted data structures of the database.

A data storage server for operating a database, the data storage server comprising:

• a processor (121) configured to:
• receive data, including encrypted security sensitive data encrypted with an encryption key, and an identifier of the encryption key from a client device, wherein the encrypted security sensitive data is to be stored in an encrypted data structure of one or more encrypted data structures of the database;
• and
• store, based on the identifier of the encryption key, the security sensitive data in the encrypted data structure of the one or more encrypted data structures of the database.