apps/protocols that use X cpu on PlanetLab can also add network artifacts.

sfmiddleman sits in the middle as a compute-intensive proxy.  sfsender
sends the middleman n "messages" each composed of m "blocks", and can
pause for t1 and t2 times at microsecond granularity after each block send
and msg send.  sfmiddleman reads blocks and does operations on them
(default is decrypt/encrypt, can also do only encrypt), then forwards them
to all connected receivers.  You guessed it, sfreceiver connects to
sfmiddleman and reads blocks and prints timestamps.  For each op on a
block, sfmiddleman notes the number of microseconds taken by the crypto
ops, and the timestamp when it/they finished, and prints those.

There is one known bug.  I'll fix it in the morning.  If there are others,
I'll get them then too.