CDR: deniable encryption

in a follow-up to the recent discussion (mostly between Riad Wahby and myself) I have decided to code an example implementation and have most of the details down. however, there are some crypto-related specifics I'm lacking. if anyone can help, I'd be happy. most importantly, is there an implementation of rivest's "all-or-nothing package thingy? this is definitely something I want, since it greatly strengthens the chaffing-like approach I'll be using. however, I don't feel confident enough to create it myself.