Patent ID: 8782804

Claim:
A storage device comprising: a nonvolatile semiconductor memory configured to store user data received from an authorized host device; an authentication information storage configured to store first apparatus authentication information to authenticate the authorized host device, and first user authentication information to authenticate an authorized user who uses the authorized host device; an apparatus authenticator configured to execute apparatus authentication according to whether second apparatus authentication information received from a currently connected host device matches the first apparatus authentication information stored in the authentication information storage; a user authenticator configured to execute user authentication, after the apparatus authentication, according to whether second user authentication information received from the currently connected host device matches the first user authentication information stored in the authentication information storage; a data read controller configured to output user data stored in the nonvolatile semiconductor memory to the currently connected host device, in response to a read request therefrom, if both of the apparatus authentication and user authentication are passed and the currently connected host device is authorized as the authorized host device; a user data invalidator configured to execute an invalidation process for physically corrupting the user data stored in the nonvolatile semiconductor memory thereby the user data cannot be read out as its original form, if at least one of the apparatus authentication and user authentication is failed; a volatile memory in which data is erased when a power supply is turned off; a portion key storage configured to store a first portion key constituting a portion of an encryption key written in the volatile memory; and a portion key writer configured to generate a third portion key on the basis of a second portion key received from the currently connected host device and the first portion key stored in the authentication information storage, after the apparatus authentication and before the user authentication, and to write the generated third portion key in the volatile memory, wherein the apparatus authenticator destructs the first portion key, if the apparatus authentication is failed, and the user authenticator uses the third portion key in the user authentication.