@node UsecaseAirgap
@cindex air-gap
@section Highly secure isolated air-gap computers

If you worry much about security, then air-gapped computer could be the
only choice you can afford. Computer without any modems, wired and
wireless networks. Obviously the only possibility to exchange mail and
files is to use physically removable storage devices like CD-ROM, hard
drive, SD, tape and USB flash drives (@strong{worst} choice, due to
those devices complexity).

Presumably you have got another own hop before that computer: another
intermediate node which performs basic verification of retrieved storage
devices, possibly by rewriting the data from USB/hard drives to CD-RWs.

NNCP supports packets relying (transitioning) out-of-box.

@verbatim
neigh: {
  bob: {
    [...]
    addrs: {
      lan: "[fe80::5400%igb0]:5400"
    }
  }
  bob-airgap:
    [...]
    via: ["bob"]
  }
}
@end verbatim

That @ref{Configuration, configuration file} tells that we have got two
known neighbours: @emph{bob} and @emph{bob-airgap}. @emph{bob} can be
reached via online connection using @emph{lan} address.
@emph{bob-airgap} can be reached by sending intermediate relay packet
through the @emph{bob}.

Any command like @command{@ref{nncp-file} myfile bob-airgap:} will
automatically create an encapsulated packet: one for the destination
endpoint, and other carrying it for intermediate relaying node.

Pay attention that relaying node knows nothing about the packet inside,
but just its size and priority. Transition packets are encrypted too:
using well-known @url{https://en.wikipedia.org/wiki/Onion_routing, onion
encryption} technology. @emph{bob} can not read @emph{bob-airgap}'s packets.
