Cryptology ePrint Archive: Report 2002/182

Oblivious Keyword Search

Wakaha Ogata and Kaoru Kurosawa

Abstract: In this paper, we introduce a notion of Oblivious Keyword Search ($OKS$). Let $W$ be the set of possible keywords. In the commit phase, a database supplier $T$ commits $n$ data. In each transfer subphase, a user $U$ can choose a keyword $w \in W$ adaptively and find $Search(w)$ without revealing $w$ to $T$, where $Search(w)$ is the set of all data which includes $w$ as a keyword.

We then show two efficient protocols such that the size of the commitments is only $(nB)$ regardless of the size of $W$, where $B$ is the size of each data. It is formally proved that $U$ learns nothing more and $T$ gains no information on the keywords which $U$ searched. We further present a more efficient adaptive $OT_k^n$ protocol than the previous one as an application of our first $OKS$ protocol.

Category / Keywords: cryptographic protocols / oblivious transfer

Publication Info: Journal of Complexity, Vol.20 [2-3], pp. 356-371 (2004)

Date: received 26 Nov 2002, last revised 8 Mar 2004

Contact author: kurosawa at cis ibaraki ac jp

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Version: 20040309:004415 (All versions of this report)

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