GoAT: File Geolocation via Anchor Timestamping.

Blockchain systems are rapidly gaining traction. Decentralized storage systems like Filecoin are a crucial component of this ecosystem that aim to provide robust file storage through a Proof of Replication (PoRep) or its variants. However, a PoRep actually offers limited robustness. Indeed if all the file replicas are stored on a single hard disk, a single catastrophic event is enough to lose the file. We introduce a new primitive, Proof of Geo-Retrievability or in short PoGeoRet, that enables proving that a file is located within a strict geographic boundary. Using PoGeoRet, one can trivially construct a PoRep by proving that a file is in several distinct geographic regions. We define what it means for a PoGeoRet scheme to be complete and sound, in the process making important extensions to prior formalism. We propose GoAT, a practical PoGeoRet scheme to prove file geolocation. Unlike previous geolocation systems that rely on trusted-verifiers, GoAT uses public timestamping servers on the internet as geolocation anchors, tolerating a local threshold of dishonest anchors. GoAT internally uses a communicationefficient Proof-of-Retrievability (PoRet) scheme in a novel way to achieve constant-size PoRet-component in its proofs. We validate GoAT’s practicality by conducting an initial measurement study to find usable anchors and also perform a real-world experiment. The results show that a significant fraction of the internet can be used as anchors and that GoAT achieves geolocation radii as low as 500km.