  We report the full implementation of a quantum cryptography protocol using a
stream of single photon pulses generated by a stable and efficient source
operating at room temperature. The single photon pulses are emitted on demand
by a single nitrogen-vacancy (NV) color center in a diamond nanocrystal. The
quantum bit error rate is less that 4.6% and the secure bit rate is 9500
bits/s. The overall performances of our system reaches a domain where single
photons have a measurable advantage over an equivalent system based on
attenuated light pulses.
