  Global quantum secure communication can be achieved using quantum key
distribution (QKD) with orbiting satellites. Established techniques use
attenuated lasers as weak coherent pulse (WCP) sources, with so-called
decoy-state protocols, to generate the required single-photon-level pulses.
While such approaches are elegant, they come at the expense of attainable final
key due to inherent multi-photon emission, thereby constraining secure key
generation over the high-loss, noisy channels expected for satellite
transmissions. In this work we improve on this limitation by using true
single-photon pulses generated from a semiconductor quantum dot (QD) embedded
in a nanowire, possessing low multi-photon emission ($<10^{-6}$) and an
extraction system efficiency of -15 dB (or 3.1%). Despite the limited
efficiency, the key generated by the QD source is greater than that generated
by a WCP source under identical repetition rate and link conditions
representative of a satellite pass. We predict that with realistic improvements
of the QD extraction efficiency to -4.0 dB (or 40%), the quantum-dot QKD
protocol outperforms WCP-decoy-state QKD by almost an order of magnitude.
Consequently, a QD source could allow generation of a secure key in conditions
where a WCP source would simply fail, such as in the case of high channel
losses. Our demonstration is the first specific use case that shows a clear
benefit for QD-based single-photon sources in secure quantum communication, and
has the potential to enhance the viability and efficiency of satellite-based
QKD networks.
