  National or international maritime authorities are used to handle requests
for licenses for all kinds of marine activities. These licenses constitute
authorizations limited in time and space, but there is no technical security
service to check for the authorization of a wide range of marine assets. We
have noted secure AIS solutions suitable for more or less constantly
internet-connected assets such as ships with satellite connections. The
additional constraints posed by underwater autonomous assets, namely less power
and connectivity, can be mitigated by using symmetric cryptography. We propose
a security service that allows the automatized check of asset authorization
status based on large symmetric keys. Key generation can take place at a
central authority according to the time and space limitations of a license,
i.e. timestamped and geocoded. Our solution harnesses the exceptionally large
key size of the RC5 cipher and the standardized encoding of geocells in the
Open Location Code system. While we developed and described our solution for
offshore underwater use, aerial and terrestrial environments could also make
use of it if they are similarly bandwidth constrained or want to rely on
quantum-resistant and computationally economic symmetric methods.
