  Single photon sources (SPS) are a fundamental building block for optical
implementations of quantum information protocols. Among SPSs, multiple crystal
heralded single photon sources seem to give the best compromise between high
pair production rate and low multiple photon events. In this work, we study
their performance in a practical quantum key distribution experiment, by
evaluating the achievable key rates. The analysis focuses on the two different
schemes, symmetric and asymmetric, proposed for the practical implementation of
heralded single photon sources, with attention on the performance of their
composing elements. The analysis is based on the protocol proposed by Bennett
and Brassard in 1984 and on its improvement exploiting decoy state technique.
Finally, a simple way of exploiting the post-selection mechanism for a passive,
one decoy state scheme is evaluated.
