According to one embodiment, a storage system includes a host device and a secure storage. The host device and the secure storage produce a bus key which is shared only by the host device and the secure storage by authentication processing, and which is used for encoding processing. The host device produces a message authentication code including a message which can be stored in the secure storage based on the bus key, and sends the produced message authentication code to the secure storage. The secure storage stores the message included in the message authentication code in accordance with instructions of the host device. The host device verifies whether the message stored in the secure storage is intended contents.