Privacy-Preserving Resource Sharing Using Permissioned Blockchains

In a resource sharing system users offer goods and services with specified conditions that if met, the access will be granted. Traditional resource sharing systems use a trusted intermediary that mediates users’ interactions. Our work is motivated by a decentralized resource sharing platform (proposed in WTSC’20) that uses a permissioned blockchain to allow users to share their digital items with their specified attributed-based access policies that are enforced through a set of smart contracts, and removes the need for a trusted intermediary. The system however allows users’ accesses to be traced, and has limited availability as access to a resource requires its owner to be on-line. We design a decentralized attribute-based access control system that achieves the same functionality while preserving the privacy of user’s access, and automating access which removes the need for the resource owner to be online. We use two cryptographic primitives, Ciphertext Policy Attribute-Based Encryption (CP-ABE), and ring signatures, and design smart contracts that allow specification and cryptographic enforcement of the users’ specified policies. We analyze the security and privacy of the system, provide the description of smart contracts and give a proof of concept implementation of the smart contracts and cryptographic algorithms that are used in the system. Our design and implementation are general and can be used for privacy-preserving resource sharing with fine-grained access control in other settings including data and information sharing among collaborating parties.