  We tackle the challenge of reliably determining the geo-location of nodes in
decentralized networks, considering adversarial settings and without depending
on any trusted landmarks. In particular, we consider active adversaries that
control a subset of nodes, announce false locations and strategically
manipulate measurements. To address this problem we propose, implement and
evaluate VerLoc, a system that allows verifying the claimed geo-locations of
network nodes in a fully decentralized manner. VerLoc securely schedules
roundtrip time (RTT) measurements between randomly chosen pairs of nodes.
Trilateration is then applied to the set of measurements to verify claimed
geo-locations. We evaluate VerLoc both with simulations and in the wild using a
prototype implementation integrated in the Nym network (currently run by
thousands of nodes). We find that VerLoc can localize nodes in the wild with a
median error of 60 km, and that in attack simulations it is capable of
detecting and filtering out adversarial timing manipulations for network setups
with up to 20 % malicious nodes.
