Diagram of spiped protecting SMTP

To set up an encrypted and authenticated pipe for sending email between
two systems (in the author’s case, from many systems around the
internet to his central SMTP server, which then relays email to the
rest of the world), one might run

dd if=/dev/urandom bs=32 count=1 of=keyfile
spiped -d -s '[]:8025' -t '[]:25' -k keyfile

on a server and after copying keyfile to the local system, run

spiped -e -s '[]:25' -t $SERVERNAME:8025 -k keyfile

at which point mail delivered via localhost:25 on the
local system will be securely transmitted to port 25 on the server
(which is configured to relay mail which arrives from but
not from other addresses).

Diagram of spiped protecting ssh

You can also use spiped to protect SSH servers from attackers: Since
data is authenticated before being forwarded to the target, this can
allow you to SSH to a host while protecting you in the event that
someone finds an exploitable bug in the SSH daemon — this serves the
same purpose as port knocking or a firewall which restricts source IP
addresses which can connect to SSH. On the SSH server, run

dd if=/dev/urandom bs=32 count=1 of=/etc/ssh/spiped.key
spiped -d -s '[]:8022' -t '[]:22' -k /etc/ssh/spiped.key

then copy the server’s /etc/ssh/spiped.key to
~/.ssh/spiped_HOSTNAME_key on your local system and add
the lines

ProxyCommand spipe -t %h:8022 -k ~/.ssh/spiped_%h_key

to the ~/.ssh/config file. This will cause ssh
to automatically connect using the spipe client via
the spiped daemon; you can then firewall off all incoming traffic on
port tcp/22.

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