System and method for restricting the use of a package of distributed application software

There is disclosed a system for permitting only an authentic user to play a desired application contained in a distributed application package. The system comprises a client for playing an application under the control of a server connected with the client through a communication network. The application package (the volume) includes control data and/or a control program. Some pieces of the control data such as an issue number (30) issued to each volume of the kind in an issued order, a user's public key-encrypted encryption key, server's public key, etc. are added by a distributor at the time of distribution of the volume. This feature makes the system flexible. There is also disclosed a stand-alone system and a security-raised data transmission technique suited for a transmission of precious information such as a credit card number.