  A novel protocol - measurement-device-independent quantum key distribution
(MDI-QKD) - removes all attacks from the detection system, the most vulnerable
part in QKD implementations. In this paper, we present an analysis for
practical aspects of MDI-QKD. To evaluate its performance, we study various
error sources by developing a general system model. We find that MDI-QKD is
highly practical and thus can be easily implemented with standard optical
devices. Moreover, we present a simple analytical method with only two
(general) decoy states for the finite decoy-state analysis. This method can be
used directly by experimentalists to demonstrate MDI-QKD. By combining the
system model with the finite decoy-state method, we present a general framework
for the optimal choice of the intensities of the signal and decoy states.
Furthermore, we consider a common situation, namely asymmetric MDI-QKD, in
which the two quantum channels have different transmittances. We investigate
its properties and discuss how to optimize its performance. Our work is of
interest not only to experiments demonstrating MDI-QKD but also to other
non-QKD experiments involving quantum interference.
