Paper 2009/268

Dealer-Free Dynamic Secret Sharing Schemes with Unconditional Security

Mehrdad Nojoumian and Douglas R. Stinson

Abstract

We propose a dealer-free dynamic secret sharing scheme where the threshold and the secret can be changed multiple times to arbitrary values after the scheme's initialization. Our motivation is to tackle the following problems. In a threshold scheme, the sensitivity of the secret as well as the number of players may fluctuate due to various reasons, e.g., the structure of the players' organization might be changed. A possible solution to this problem is to modify the threshold and/or change the secret. Moreover, a common problem with almost all secret sharing schemes is that they are ``one-time'', meaning that the secret and shares are known to everyone after secret recovery. This problem could be resolved if the dealer shares various secrets at the beginning, but a better solution is to dynamically generate new secrets in the absence of the dealer. As our contribution, the well-known re-sharing techniques are analyzed in both passive and active adversary models. Subsequently, our solution for a dealer-free dynamic secret sharing scheme is provided. Finally, a new secret sharing protocol, as an applications of our dynamic scheme, is proposed.