Patent ID: 7031946

Claim:
A contactless IC tag that has a nonvolatile memory and is read and written contactlessly using radio waves, the contactless IC tag being attached to an item which passes through multiple stages of a life cycle from manufacture to disposal, the contactless IC tag comprising: storing means having stage storage areas as many as the stages of the life cycle; identifier holding means for holding stage identifiers that each identify a different one of the stage storage areas; secret receiving means for receiving an access identifier in secrecy from an external access device; judging means for judging whether the received access identifier matches one of the stage identifiers in the identifier holding means; access information receiving means for receiving access information from the access device, when the access identifier matches one of the stage identifiers; and accessing means for accessing a stage storage area that is identified by the access identifier, based on the received access information, wherein the secret receiving means includes: authenticator outputting means for generating a first authenticator and outputting the first authenticator to the access device; acquiring means for acquiring a second authenticator that is obtained by encrypting the first authenticator by an encryption algorithm using the access identifier as an encryption key, from the access device; and encrypting means for encrypting the first authenticator by the encryption algorithm using the stage identifiers each as an encryption key, to generate third authenticators, the judging means judges whether the acquired second authenticator matches one of the third authenticators, and if the second authenticator matches one of the third authenticators, judges that the access identifier matches one of the stage identifiers, and the accessing means accesses a stage storage area identified by a stage identifier which is used as an encryption key to generate the third authenticator that matches the second authenticator, as the stage storage area identified by the access identifier.