Collusion Attack Resistance and Practice-Oriented Threshold Changeable Secret Sharing Schemes

With the popularity of the Internet, the load on the servers is aggravated heavily, so secret sharing is used as a fundamental approach for improving availability of an online service. In a (t, n)-threshold secret sharing scheme, any t-out-of-n participants could recover the shared secret, and any less than t participants could get nothing about the shared secret. However, with the long life of the secret, the number of adversaries increase over time. In order to deal with this issue, one may require to increase the threshold value from t to t´(t´ > t). In the traditional, existing Threshold Changeable Secret Sharing(TCSS) schemes either required secure channel or no security analysis. Motivated by that, we propose a new practice-oriented TCSS scheme using partial broadcast channel(PBC) in both share distribution phase and secret reconstruction phase. Our protocol increases the dealer and the combiner´s communication rate and resist to collusion attack. Furthermore it is an ideal and robust threshold scheme which threshold parameters are likely to happen several times. Therefore our protocol is practice-oriented scheme.