This paper tackles an open challenge: reliably determining the geo-location of nodes in decentralized networks, considering adversarial settings and without depending on any trusted parties. 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 round trip time (RTT) measurements between randomly chosen pairs of nodes in a way that cannot be biased by an adversary. Trilateration is then applied to the set of measurements to verify claimed geo-locations. VerLoc verifies genuine locations with more than 90\% accuracy, and it is capable of detecting and filtering out adversarial timing manipulations for network setups with up to 25\% malicious nodes.
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