Re: Forward and reply messages

[Roger Dingledine <arma@mit.edu>]

> > Somewhere in here, if it's the instructions for constructing any onion,
> > should be "attach your payload if you've got one". I would guess it's
> > step 2b?
> 
> Since the headers are variable-length, the payload can just be part of the
> innermost header. When constructing a reply, the innermost header for the
> forward part of the path is the reply block (encrypted in a way that depends
> on the payload) followed by the random-looking payload.

Can you clarify this a bit? Why is the reply block encrypted
with a function of the payload? (I assume the previous list of
what-to-do-with-a-message needs to be updated to reflect this?)

Also, why is the payload random-looking? (Wouldn't the payload be in
plaintext at the point where the reply starts, and then get successively
wrapped by each hop in the reply block?)

--roger