Hey.
i wanted to make a prog that will allow me to unpack a certain format (ex. .rar etc...)....how can i do that? i wanted not just and algo how to do it, but more of how u got that algo.....
thx

For rar there's..:

http://www.rarlab.com/rar/unrarsrc-3.4.2.tar.gz

..but the general approach to figuring out an unknown (as in no hits on google) algorithm is reversing the program that does the unpacking. Breaking on & tracing from file open/read/etc calls usually gives a starting point. Also, you might want to read this thread:

http://www.woodmann.net/forum/showthread.php?t=6012

well, are there any examploe of something like that being done?
maybe for a rar but with the aproach of unknown archive?
maybe someon can do a qucik explanation on how to do that(basic steps)...i mean something like rar shoudl not be that hard for ppl with exp in this area.....


so far i got this:
i but a bpx on CreateFileA(if that is waht is used for file reading), then i see where it is called and start tracing to see how it is done and then recoding it in w/e lanuage?

Read the thread that ughugh suggests above. Also, noone will give you step-by-step instructions, you need to put in some effort and learn things yourself too. You will need to have a much deeper understanding about related concepts to be able to perform something like this I'm afraid.

check out what information is already available on the subject?
http://www.wotsit.org/download.asp?f=rar202
then depending on what language you program in there may be source available to at least give you a start.

i am not asking somone to give me step by step., but an example is nice, since i never coded a archiver/unarchvier.....
anyways, gonna go read those links