Abstract: A software analysis protection method capable of preventing an illegitimate use of a software reliably, by making a software analysis difficult without complicating or enciphering the software itself. Software parts dividing the software to be used at the user terminal are distributedly stored in the user terminal and the center, and the software parts stored in the center are transmitted to the user terminal and loaded into missing parts among the software parts stored in the user terminal on a memory so as to make the software operable at the user terminal. Then, the software as developed on the memory is operated at the user terminal. The software parts are down-loaded from the center to the user terminal such that an arranged pattern of the software as developed on the memory is changed at each time of a use of the software at the user terminal.

Abstract: A method and a system for cipher key distribution realizing an effective prevention of the illegitimate use and the illegitimate charging. A key request signal containing a first random number generated at each user terminal is transmitted from each user terminal to the key center, so as to indicate the cipher key required at each user terminal to the key center, and a terminal check signal containing a second random number generated at the key center is transmitted from the key center to each user terminal.