There are two checksum related things. Checksums.java handles mio-related checksums while DSSave.java has checksum code for the DS saves themselves. It'd really be nice if someone could figure out Showcase checksums for *DATA and SYS_0/SYS_1. I have absolutely no idea what Nintendo did there or more importantly why they did it. Showcase checksums look like the first four bytes of each file, although SYS_0/SYS_1 probably have backups of *DATA's checksums. They also appear linear, but make no sense. Maybe they are masked with a unique ID or something.