  We demonstrate a post-quantum key-exchange with the nanosatellite SpooQy-1 in
low Earth orbit using Kyber-512, a lattice-based key-encapsulation mechanism
and a round three finalist in the NIST PQC standardization process. Our
firmware solution runs on an on-board computer that is based on the Atmel AVR32
RISC microcontroller, a widely used platform for nanosatellites. We uploaded
the new firmware with a 436.2 MHz UHF link using the CubeSat Space Protocol
(CSP) and performed the steps of the key exchange in several passes over
Switzerland. The shared secret key generated in this experiment could
potentially be used to encrypt RF links with AES-256. This implementation
demonstrates the feasibility of a quantum-safe authenticated key-exchange and
encryption system on SWaP constrained nanosatellites.
