Checksums

[Noctis Caelum]

I Been makin mod tools for about 2 1/2 weeks now and pretty much i can code in VB just fine..I want to make other mod tools for games that dont have Save editors..But the ones i want to do have some type of security on them and i have no clue how to figure or even recongize when a game has security (checksum) on it..So i was wondering if someone with the skill to notify and code checksums could take the time to show and explain how to work with those...thanks

[cybersam]

well... firstly... i'm too aint really good with the security stuff...
but here some basic things...

finding out what security is used.. has nothing to do with your programming skills... well at least most of the times ^-^

while this depends on your "hexing ability"
yo can still recognize a few things even if you're a beginner in hex editing...
basic things... once you open your file in the hex editor... look through it and see if you can see anything readable...

if (you find something)
    then its most likely not encrypted/compressed or at least not all of it
elseif (the hex string looks like random values from top to bottom)
    then the file is compressed or encrypted
else 
    search for values compare it with a few other files with different values
    if (you find something)
        then its most likely not encrypted/compressed or at least not all of it
    else
        look again... some people thing if they can't find anything after they converted theirs values to hex hex strings and searched for that its enough...
        but i recommend using the build in search functions of your hex editor... with some of them you can search for different Integer types, floats, doubles, text and hex string
        go through all of them when searching for values

        if (you still can't find anything)
            then its most likely compressed/encrypted
        else
            you start modifying and try to load it...
            if (you the game loads your save)
                then the file doesn't have a checksum or at least the part you edited isn't part of the checksum (this case is very rare)
            else
                the game doesn't load or tells you the file is corrupted
                from here first things to do
                check your steps if you really did everything right (modifying the right place, rehashed/resigned and such)
                if (you double checked your steps and the game still is saying the same thing)
                    then there is most definitely a checksum
                endif
            endif
        endif
    endif
endif

those are the simple steps everyone can do no matter how high your hexing skill is ^-^
when you level up your hexing skills you will be able to reduce the steps to something like this

if (compressed/encrypted)
    return "encrypted or compressed"
else
    look for values and modify
    if (there is a checksum) 
        find it and try to figure it out 
        if (it's a standard checksum)
            try to figure it out
        else 
            return look for help on the forums
    endif
endif

a bit lengthy... but i hope this helps ^-^