All game demos I downloaded to my N3DS are composed by .app, .tmd and .cmd. I learned from 3dbrew that .tmd is called“time meta data”, but what is .app? Is there any decryption tool work on Windows can decrypt them? My hack idea is to imitate how the game demo works, we can put 3DS ROM into SD card in the form of .app, .tmd and .cmd, control the remaining uses(we can modify it to 9999 ), we can use many program on N3DS if this idea gets its place. But to make this, we should know the structure of the demo and how to pass firmware's check.