Re: Forward and reply messages

[David Hopwood <david.hopwood@zetnet.co.uk>]

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Roger Dingledine wrote:
> David Hopwood wrote:
> > Roger Dingledine wrote:
> > > 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've no idea why I said that. It doesn't need to be for this design.

(Reply blocks do, however, need to be stored secretly so that they can't
be linked to later messages.)

> 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?)

It has to be random-looking because it will appear on the wire at the point
where it is sent to the first reply hop. So it should be encrypted to the
recipient, who will first undo all the wrapping, and then decrypt it.

- -- 
David Hopwood <david.hopwood@zetnet.co.uk>

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