Information-theoretically Secure Timed-release Secret Sharing Schemes

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Author(s)

    • Watanabe Yohei
    • Graduate School of Environment and Information Sciences, Yokohama National University
    • Shikata Junji
    • Graduate School of Environment and Information Sciences, Yokohama National University|Institute of Advanced Sciences, Yokohama National University

Abstract

In modern cryptography, the secret sharing scheme is an important cryptographic primitive, and it is used in various situations. In this paper, timed-release secret sharing (TR-SS) schemes with information-theoretic security is first studied. TR-SS is a secret sharing scheme with the property that more than a threshold number of participants can reconstruct a secret by using their shares only when the time specified by a dealer has come. Specifically, in this paper we first introduce models and formalization of security for two kinds of TR-SS based on the traditional secret sharing scheme and information-theoretic timed-release security. We also derive tight lower bounds on the sizes of shares, time-signals, and entities' secret-keys required for each TR-SS scheme. In addition, we propose direct constructions for the TR-SS schemes. Each direct construction is optimal in the sense that the construction meets equality in each of our bounds, respectively. As a result, it is shown that timed-release security can be realized without any additional redundancy on the share size.

Journal

  • Journal of Information Processing

    Journal of Information Processing 24(4), 680-689, 2016

    Information Processing Society of Japan

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