Fine - *but*: Every such "more complicated than I think" algorithm makes the reader uneasy: "What did I miss that it cannot be done as simple as I think? And moreover, he states this as if it is clear that my simple version is out-of-the-question ... but I don't see it" and so on etc. And modular addition, I'd claim, is in our minds all the time anyway (it is e.g. implicit in Javas and C#s and probably many other languages' int addition).

So, if want to leave it like that (not choosing to start R with 0, but XORing the random r_b with 1...256) I think we readers would be happy if you could add something like " (that way, we can keep our assumption that R was chosen randomly; of course, one can also select different R blocks that count up at the last byte from 0 to 255)".