Provided are an identity (ID)-based encryption and signature method and a terminal that use an ID of a transmitter or a receiver as a part of the filename or the extension of a file transmitted to the receiver by the transmitter. Accordingly, it is possible to enable a user to visually recognize that the file has been provided with security. Also, it is possible to designate an associated program for the extension, and the user can easily decrypt or verify the file through the designated associated program.