WIRELESS COMMUNICATIONS DEVICE AND AUTHENTICATION PROCESSING METHOD

An authentication method is provided which is capable of performing message authentication within an allowable time regardless of the magnitude of the number of messages and performing message authentication high in accuracy within a range for which the allowable time allows. Upon transmission by wireless communications with another mobile or a fixed station, a message authentication code of communication data and a digital signature are generated (S200 and S300). The generated message authentication cod and digital signature are transmitted with being added to the communication data. Upon reception, whether authentication should be done using either one of the message authentication code and the digital signature included in received information is determined according to its own state for the authentication (S400 and S500). This state includes, for example, a load state of a central processing unit or the like that performs an authentication process.