A user-worn device 10a that is to be installed in user-worn equipment 30a that can be worn by a user, and a user device 20a that is to be installed in user equipment 40a to be used by the user are employed.The original information is divided and stored as a first information segment (1) and a second information segment (2) in the user-worn device 10a and in the user device 20a (with the original information), respectively. The user-worn device 10a sends the first information segment (1) and the user device 20a combines the second information segment (2) stored in its storage with the received first information segment (1), forming a third piece of information. The identity of the user is authenticated if the third piece of information matches the original information. Once the identity of the user is authenticated, the user device 20a permits the use of the user equipment 40a.