hidden update 2

[Tom]

once again I'm asking for some details/help on what looks ever more like
a pure anonymity problem. maybe I should start with revealing what it's
all for, since I'm pretty much stuck there at the moment. point your
browser to http://www.lemuria.org/Black if you want and take a look.
there's not much there at the moment, but should be enough to give you a
basic idea. in short, it's kind of an archive for thought crime. a
little like cryptome but with a different topic and philosophy. most
importantly, it's only a front. the actual data store is somewhere else,
e.g. freenet. so when the thugs kick in my door and take the machine,
nothing whatsoever is lost.

now since some of the information archived there will surely be illegal
in one or more countries, what is needed is guaranteed anonymity for
pretty much everyone involved (except the publisher, who's taking a risk
but can drop out at any time without destroying the data). some of the
related problems are solved, many not. one of the worst unsolved so far
is what I call "hidden update".

in short, I need a way for Alice to give Bob a piece of information with
neither Alice nor Bob knowing each other. however, Bob should have a way
to verify that subsequent messages are coming from the same Alice. bonus
points if there's a way for Bob to send messages to Alice, too.

main problem: the need to implement the above with existing and readily
available infrastructure.

one solution I've come up with so far is for Alice to encrypt to Bob's
(anonymously published) key and post via remailers to, say,
alt.anonymous.messages, which Bob is known to read. alternatively, agree
on one or more porn/binary newsgroups and use stego.