SCIS 2022
2022 Symposium on
Cryptography and Information Security
Osaka, Japan & Online, Jan. 18 – 21, 2022
The Institute of Electronics,
Information and Communication Engineers

Copyright ©2022 The Institute of Electronics,
Information and Communication Engineers

A Privacy-Preserving Data Sharing Framework for Public
Blockchains
Yepeng Ding ∗Hiroyuki Sato ∗Keywords: data sharing, privacy preservation, access control, blockchain, decentralized storage

Abstract

applicability of Sunspot in practice. Furthermore, weevaluate the security and privacy of Sunspot throughtheoretical analysis and experiments.

Blockchain technology has been adopted in a wide
range of fields [3, 4, 2]. Particularly, worldwide decentralization of data persistence and sharing is advancing with the evolution of public blockchain technologies, as can be seen by the boom of decentralized applications (DApp). These DApps have presented a setof attractive properties including accessibility, automation, transparency, interoperability, finality, borderlessness, and innovativeness. These properties are generally achieved through on-chain data persistence andsharing supported by transparent public blockchainssuch as Ethereum [5] that are permissionless and fully
disclose all types of data.
However, full transparency may lead to privacy issues. Besides, the on-chain persistence of large data
is significantly expensive technically and economically.
These issues lead to the difficulty of sharing fairly large
private data while preserving attractive properties ofpublic blockchains. Although direct encryption for onchain data persistence can introduce confidentiality,
new challenges such as key sharing, access control, andlegal rights proving are still open. Meanwhile, crosschain collaboration still requires secure and effective
protocols, though decentralized storage systems suchas IPFS [1] bring the possibility for fairly large data
persistence.
In this paper, we propose Sunspot, a decentralized
framework for privacy-preserving data sharing with access control on transparent public blockchains, to solvethese issues. Sunspot protocols are generalized to be
independent of blockchain platforms and support multiple access control mechanisms to enable flexible data
sharing in various scenarios. Particularly, we show
an identity management model and a managementfree model for identification based on two different access control mechanisms. Besides, we present MyPub,
a decentralized privacy-preserving publishing platform
based on Sunspot to demonstrate the practicality andReferences[1] Juan Benet. Ipfs-content addressed, versioned, p2p
file system. arXiv preprint arXiv:1407.3561, 2014.
[2] Yepeng Ding and Hiroyuki Sato. Bloccess: towards fine-grained access control using blockchain
in a distributed untrustworthy environment. In
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[3] Yepeng Ding and Hiroyuki Sato. Dagbase: a decentralized database platform Using DAG-based consensus. In 2020 IEEE 44th Annual Computers,
Software, and Applications Conference (COMPSAC), pages 798–807. IEEE, 2020.
[4] Yepeng Ding and Hiroyuki Sato. Derepo: a distributed privacy-preserving data repository withdecentralized access control for smart health. In
2020 7th IEEE International Conference on Cyber
Security and Cloud Computing (CSCloud)/2020 6thIEEE International Conference on Edge Computing
and Scalable Cloud (EdgeCom), pages 29–35. IEEE,
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[5] Gavin Wood. Ethereum: A secure decentralised
generalised transaction ledger. Ethereum projectyellow paper, 151(2014):1–32, 2014.

∗ The University of Tokyo, 7 Chome-3-1 Hongo, Bunkyo City,

Tokyo 113-8654, Japan{youhoutei,schuko}@satolab.itc.u-tokyo.ac.jp1