[Cryptography] Firewall penetration

[Jason Richards]

> Suppose a server talks to two clients, which are connected to the 
> internet by ordinary consumer type connections.  Is their any
> reliable, practical, generally useful way whereby it can arrange for
> the two clients to talk directly to each other, or is it more
> practical for all data to be stored on the server by one client, and
> then collected by the other client?
> 
> When last I looked at this issue, direct communication was getting 
> harder, and workarounds were like bugs that were likely to be fixed.

PC remote control services such as GoToMyPC, TeamViewer and LogMeIn
avoid direct communications and proxy the connections through a central
server. This means that standard home routers can have a firewall
denying all inbound connections and utilise simple NAT configurations,
but still allow a remote device to connect "in". In practice, both ends
of the connection connect out to the central server which acts as a
switchboard to establish a circuit.

Tor hidden services can be used to achieve the same thing.

J