What is a checksum?
what role does it play?
how does one find and "Fix" the checksum?
sorry for all the Q's
T
a checksum is like...
say the game save data is '012345' (simple yeah)
the checksum could be 'add up all the numbers' - so we would get a checksum of '15'. (0+1+2+3+4+5)
so, the whole savedata, included the checksum would be '012345
15'.
when the game checks the save, it does a check on the data and the checksum, so it checks if '012345' actually adds up to '15'. if so, good.
if not, the save is corrupt, maybe the memory card is bad... etc etc. it's not only to prevent hackers.
if we want to edit the game save, for example we change the first byte of data to '99' -> '
992345'.
including the checksum, the whole save would be '992345
15' - that '15' is the old checksum, we need to calculate it again!
of course in this example it is easy, just add up the number etc...
but it's not that simple for games, we might not know what data is used to calculate the checksum (all the game save, half of it?)
we might not know how big the checksum is and where it is located in the save
we might not know the method to calculate the checksum.
usually it's not too hard i think, many times it could just be some crc/sha/md5 sum i believe, but i'm sure sometimes it is not so simple.