A storage device that can be attached and/or detached to and/or from an information-processing device is provided. The storage device includes a storage unit including a first area provided to store an encryption key used to encode first information and first authentication information used to perform authentication, and a second area storing second information encoded by the information-processing device by using the encryption key, an authentication unit configured to authenticate a user based on second authentication information generated by the information-processing device based on third information input by the user and the first authentication information, a transmission unit configured to transmit the encryption key to the information-processing device when validity of the user is confirmed through the authentication, and a control unit configured to have control over writing and/or reading the encoded second information into and/or from the second area.