ORBITAL-KEY: A Satellite-Witnessed Key Agreement Protocol for Terrestrial Nodes Using Shared Orbital Observation

We present ORBITAL-KEY, a key agreement protocol that enables two terrestrial nodes to independently derive identical cryptographic key material without transmitting any secret over the network. The protocol exploits the deterministic, publicly verifiable, and time-sensitive positions of Low Earth Orbit (LEO) satellites as a shared physical witness. Both nodes independently compute satellite ECEF positions from public TLE data, apply a quantization function to achieve timing robustness, and pass the resulting material through a standard HKDF construction supplemented by a publicly available geomagnetic index binding. No orbital infrastructure beyond passive observation of public ephemeris data is required. Update notice: An updated version of this paper (v1.1, 12 March 2026) has been published, adding Section VIII: Proof-of-Concept Results with empirical validation of the protocol. Available at: https://doi.org/10.5281/zenodo.18989984