## Cryptology ePrint Archive: Report 2011/241

A Novel Adaptive Proactive Secret Sharing without a Trusted Party

Xiuqun Wang

Abstract: A $(t+1,n)$ proactive secret sharing is to protect a secret in long-lived system by distributing it to a group of $n$ participants and refreshing their shares periodically in this fixed group, while any $t+1$ and more than $t+1$ shares can reconstruct the secret. In some environment, it needs to change not only the number of participants $n$ but also the threshold value $t$. An adaptive proactive secret sharing is to refresh the shares as $t$ and $n$ change. In this paper, we propose a novel adaptive proactive secret sharing scheme without a trusted party. Our proposed scheme is uniformly efficient and tolerates $t$ Byzantine faults in any single time interval, where the number of participants $n\geq 3t+1$. The threshold value $t$ and the number of participants $n$ can be changed arbitrarily in two adjacent intervals. We also prove that our proposed scheme is secure under the discrete logarithm intractability assumption.

Category / Keywords: cryptographic protocols / proactive secret sharing, Byzantine agreement protocol