Publications

Conference Papers

  • Timed-Release Secret Sharing Schemes with Information Theoretic Security
    Author(s)
    Y. Watanabe and J. Shikata
    Conference
    BalkanCryptSec 2014
    Vol.
    LNCS 9024
    Pages
    219–236
    Publisher
    Springer
    Publication Year
    2014
    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 participants more than a threshold number 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 the timed-release security can be realized without any additional redundancy on the share size.