  Measurement-device-independent quantum key distribution with a finite number
of decoy states is analyzed under finite-data-size assumption. By accounting
for statistical fluctuations in parameter estimation, we investigate
vacuum+weak- and vacuum+two-weak-decoy-state protocols. In each case, we find
proper operation regimes, where the performance of our system is comparable to
the asymptotic case for which the key size and the number of decoy states
approach infinity. Our results show that practical implementations of this
scheme can be both secure and efficient.
