Oblivious keyword search with authorization

Oblivious keyword search (OKS) allows a user to search and retrieve the data associated with a chosen keyword in an oblivious way. The database supplier issues a trapdoor (used for searching) of a specific keyword chosen by the user while learns nothing about this keyword. In this paper, we propose a new cryptographic primitive called oblivious keyword search with authorization (OKSA). In OKSA, the supplier is able to verify the to-be-search keyword belonging to the authorized keyword set for a user before running the OKS protocol. The proposed OKSA augments the traditional OKS by providing assurance of keyword authorization besides oblivious search. Then we present an OKSA protocol and formally prove its security. The proposed protocol features with one-round (two-pass) interaction and constant size communication cost between the supplier and the user in the transfer phase. Precisely, the communication cost nseeds only four group elements (three group elements for keyword token and proof, and one group element for assigned trapdoor), independent of the size of authorized keyword set

The study on the agricultural history in China, by Motonosuke Amano

Blockchain-based distributed storage enables users to share data without the help of a centralized service provider. Decentralization eliminates traditional data loss brought by compromising the provider, but incurs the possible privacy leakage in a way that the supplier directly links the retrieved data to its ciphertext. Oblivious keyword search (OKS) has been regarded as a solution to this issue. OKS allows a user to retrieve the data associated with a chosen keyword in an oblivious way. That is, the chosen keyword and the corresponding ciphertext are unknown to the data supplier. But if the retrieval privilege is with an authorized keyword set, OKS is unavailable due to one-keyword restriction and public key encryption with keyword search (PEKS) might lead to high bandwidth consumption. In this paper, we introduce Searchain, a blockchain-based keyword search system. It enables oblivious search over an authorized keyword set in the decentralized storage. Searchain is built on top of a novel primitive called oblivious keyword search with authorization (OKSA), which provides the guarantee of keyword authorization besides oblivious search. We instantiate a provably secure OKSA scheme, featured with one-round interaction and constant size communication cost in the transfer phase. We apply OKSA and ordered multisignatures (OMS) to present a Searchain protocol, which achieves oblivious peerto-peer retrieval with order-preserving transaction. The analysis and evaluation show that Searchain maintains reasonable cost without loss of retrieval privacy, and hence guarantees its practicality