A novel threshold changeable secret sharing scheme

A (t, n) threshold secret sharing scheme is a fundamental tool in many security applications such as cloud computing and multiparty computing. In conventional threshold secret sharing schemes, like Shamir’s scheme based on a univariate polynomial, additional communication key share scheme is needed for shareholders to protect the secrecy of their shares if secret reconstruction is performed over a network. In the secret reconstruction, the threshold changeable secret sharing (TCSS) allows the threshold to be a dynamic value so that if some shares have been compromised in a given time, it needs more shares to reconstruct the secret. Recently, a new secret sharing scheme based on a bivariate polynomial is proposed in which shares generated initially by a dealer can be used not only to reconstruct the secret but also to protect the secrecy of shares when the secret reconstruction is performed over a network. In this paper, we further extend this scheme to enable it to be a TCSS without any modification. Our proposed TCSS is dealer-free and non-interactive. Shares generated by a dealer in our scheme can serve for three purposes, (a) to reconstruct a secret; (b) to protect the secrecy of shares if secret reconstruction is performed over a network; and (c) to enable the threshold changeable property.