Example of use (with nacl-20110221/build/*/bin in $PATH):
  curvecpmakekey serverkey
  curvecpprintkey serverkey > serverkey.hex
  curvecpserver this.machine.name serverkey \
    127.0.0.1 10000 31415926535897932384626433832795 \
      curvecpmessage cat /usr/share/dict/words &
  curvecpclient this.machine.name `cat serverkey.hex` \
    127.0.0.1 10000 31415926535897932384626433832795 \
      curvecpmessage -c sh -c 'nacl-sha512 <&6'
  nacl-sha512 < /usr/share/dict/words