Kusabax-idcrack is a project mainly written in C, it's free.
Exploiting Kusaba X's insecure "Poster ID" algorithm.
Currently, Kusaba X and a lot of Kusaba X ports use a very insecure algorithm for calculating "Poster IDs". That is, a semi-unique ID used as a means of identification. Unfortunately, the developers must have overlooked the major flaw in the algorithm when developing the function. The poster IDs are calculated by simply truncating an (unsalted) MD5 hash of the dotted decimal representation of the user's IP address to 6 characters. As there are 232 IPv4 addresses and only 224 possible IDs, it makes it possible (and incredibly easy) to narrow an ID down to ~256 IP addresses. Ignoring multicast, private and reserved address spaces (see below) brings it down to ~221 possible addresses. The rest could possibly be eliminated using GeoIP or any other means.
Although it may seem unpractical because of the time and processing power required to test a hash against every single IP address, it could be done in just minutes with a large rainbow table.
In short, this simple program will turn a standard Kusaba X "Poster ID" into ~221 possible IPv4 addresses.
After excluding multicast, private and reserved space, there are 3 706 584 831 addresses (~14% deduction).
To compile, use make.
To generate the rainbow table, use ./ids <database filename> --generate. Depending on disk and CPU speeds, this may take a few minutes (or even hours), but only needs to be done once. This will produce a 21GB file.
To decode an ID, use ./ids <database> <poster id>. All possible IPv4 addresses will be printed to standard output line by line. Again depending on CPU and disk speeds, this may take a few minutes.