Cryptology ePrint Archive: Report 2021/697

GoAT: File Geolocation via Anchor Timestamping

Deepak Maram and Iddo Bentov and Mahimna Kelkar and Ari Juels

Abstract: 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 "GeoPoRet", that enables proving that a file is located within a strict geographic boundary. Using GeoPoRet, one can trivially construct a PoRep by proving that a file is in several distinct geographic regions. We define what it means for a GeoPoRet scheme to be complete and sound, in the process making important extensions to prior formalism.

We propose GoAT, a practical GeoPoRet scheme to prove file geolocation. Unlike previous geolocation systems that rely on trusted-verifiers, GoAT bootstraps using public timestamping servers on the internet that serve as geolocation anchors, tolerating a local threshold of dishonest anchors. GoAT internally uses a communication-efficient 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 GoAT anchors. Furthermore, GoAT achieves geolocation radii as little as 1000km.

Category / Keywords: cryptographic protocols / file location, proof of retrievability, zero knowledge

Date: received 26 May 2021, last revised 20 Aug 2021

Contact author: sm2686 at cornell edu

Available format(s): PDF | BibTeX Citation

Note: add fig. 1, fix CCS reviewer comments

Version: 20210820:211915 (All versions of this report)

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