I selected a random cam. If you want another let me know.
Thx. Nafraf already sent me the files for his a810. I have unscrambled the diskboot file using the appropriate camera routine (easier than trying to work out how to "undance" based on the dancingbits CHDK tool). There are not a lot of strings inside, the interesting ones are:
InitCHDKPTP
SpyTaskAlso, since .rbf is not a widely known font format, they are likely using those routines too. The CHDK PTP support exists since end of 2010. So, they took a relatively early CHDK tree, kept what they needed and added their stuff. CHDK or source is not mentioned on their site, so IMHO they are violating the license. I already mentioned that their PC software likely uses libgphoto code.
edit:
I can't find "rbf" in the binary, the file might be a leftover from an early build.