Ideal Secret Sharing Schemes with Share Selectability

In this paper, we investigate a new concept, called share selectable secret sharing, where no unauthorized set can obtain information of the secret (in the information-theoretic sense) even if shares are selectable as arbitrary values which are independent of the secret. We propose two totally selectable (i.e., all users’ shares are selectable) secret sharing schemes with unanimous structure. We also propose a quasiselectable (i.e., a part of each user’s share is selectable) secret sharing scheme with certain hierarchical structures which contains special cases of the hierarchical threshold structures introduced by Tamir Tassa in TCC2004 (or its full version (J. Cryptology2007)). If all selectable shares are randomly chosen, then our schemes are perfect. Finally, we discuss the effect of the leakage information of the secret if a weak secret is indicated as a selectable share.