A method of preparing memory contents of a gaming machine for subsequent authentication and a method of authenticating the prepared memory contents are disclosed. A first memory stores a game data set and a first authentication code generated from the game data set. The game data set includes game data files and second authentication codes generated from the respective data files. A second memory stores an authentication program for authenticating the first memory's contents, as well as a third authentication code generated from the second memory's contents. To authenticate the memory contents, the second memory's contents are first authenticated and, if deemed authentic, the game data set as a whole and each data file in the first memory are authenticated. The authentication process involves generating fresh authentication codes using the authentication program and comparing the fresh codes with appropriate ones of the stored authentication codes.