  We report on a complete experimental implementation of a quantum key
distribution protocol through a free space link using polarization-entangled
photon pairs from a compact parametric down-conversion source. Over 10 hours of
uninterrupted communication between sites 1.5 km apart, we observe average key
generation rates of 630 per second after error correction and privacy
amplification. Our scheme requires no specific hardware channel for
synchronization apart from a classical wireless link, and no explicit random
number generator.
