A client system includes a client-side host device, and a client-side storage device including a storage controller and a storage memory. The storage controller includes a host interface, a processor configured to control a read operation and a write operation for the storage memory, and a homomorphic encryption and decryption accelerator configured to, based on receiving a read request from the client-side host device, perform homomorphic encryption on first plaintext data that is read from the storage memory, to generate first homomorphic ciphertext data, and provide the first homomorphic ciphertext data to the client-side host device through the host interface, and based on receiving a write request from the client-side host device, perform homomorphic decryption on second homomorphic ciphertext data that is received through the host interface, to generate second plaintext data, and write the second plaintext data in the storage memory.