  The relatively low key rate seems to be the major barrier to its practical
use for the decoy state measurement device independent quantum key distribution
(MDIQKD).
  We present a 4-intensity protocol for the decoy-state MDIQKD that hugely
raises the key rate, especially in the case the total data size is not large.
  Also, calculation shows that our method makes it possible for secure private
communication with {\em fresh} keys generated from MDIQKD with a delay time of
only a few seconds.
