Matthew Garrett
Christmas is a time to ignore such trifling details as nearly accidently burning the house down, and instead to focus on what's important in life - working out which hoops to jump through to make new hardware useful without installing less convenient operating systems. This year was more straightforward than some, and merely involved attempting to work out how to give people money in return for books that could then be read on my Sony reader thingy. Shockingly enough, the Sony Ebook Store requires a windows app, so not a good start. There's no shortage of sites that sell ebooks in a variety of formats without any platform dependent awkwardness, though - of course, most of them are inconveniently DRMed. And the only DRMed content the Sonys will read is either Sony's own or some encrypted PDFs[1].Not to worry - the DRMed version of the Mobipocket format is based on a symmetric encryption algorithm from 1991, so finding a way around that isn't much of a problem[2]. The only real issue I had was generating the PID needed to buy one of the damn things in the first place. This 10 character string is generated when you install the Mobipocket reader software, but doing so would again involve Windows.
So here's a trivial C program that generates valid PIDs with working checksums. The PID on its own isn't a secret (given that you can get as many as you want by reinstalling the Windows software), so I can't see any awkward copyright law things going on. And, really, it's just a random string plus a checksum.
CRC code is from SSH, the checksum validation is a reimplementation of code from EBook::Tools::Mobipocket by Zed Pobre. My total creative input was generating a 7 character random string and sticking a dollar sign at the end. Go me.
[1] According to the blurb about the firmware update, though mine still seems to claim that it's not authorised to read DRMed content in the about screen. Possibly it needs keys generating, or something
[2] No, I'm not going to tell you how. The internet exists so you can work these things out without asking me