  Cloud computing is a powerful and popular information technology paradigm
that enables data service outsourcing and provides higher-level services with
minimal management effort. However, it is still a key challenge to protect data
privacy when a user accesses the sensitive cloud data. Privacy-preserving
database query allows the user to retrieve a data item from the cloud database
without revealing the information of the queried data item, meanwhile limiting
user's ability to access other ones. In this study, in order to achieve the
privacy preservation and reduce the communication complexity, a quantum-based
database query scheme for privacy preservation in cloud environment is
developed. Specifically, all the data items of the database are firstly
encrypted by different keys for protecting server's privacy, and in order to
guarantee the clients' privacy, the server is required to transmit all these
encrypted data items to the client with the oblivious transfer strategy.
Besides, two oracle operations, a modified Grover iteration, and a special
offset encryption mechanism are combined together to ensure that the client can
correctly query the desirable data item. Finally, performance evaluation is
conducted to validate the correctness, privacy, and efficiency of our proposed
scheme.
