## Cryptology ePrint Archive: Report 2020/1035

Evolving Secret Sharing with Essential Participants

Abstract: Komargodski et.al. introduced {\em Evolving Secret Sharing} which allows an imaprtial participant, called \emph{dealer}, to share a secret among unbounded number of participants over any given access structure. In their construction for evolving secret sharing over general access structure, the size of share of the $i^{th}$ participant happens to be exponential $(\mathcal{O}(2^{i-1}))$. They also provided constructions for $(k,\infty)$ threshold secret sharing. We consider the problem of evolving secret sharing with $t$ essential participants, namely, over $t$-$(k,\infty)$ access structure, a generalization of $(k,\infty)$ secret sharing $(t=0)$. We further generalize this access structure to a possible case of unbounded number of essential participants and provide a construction for secret sharing on it. Both the constructions are information theoretically secure and reduce the share size of the construction due to Komargodski et.al. over general access structure, exponentially. Moreover, the essential participants receive ideal (and hence, optimal) shares in the first construction.

Category / Keywords: cryptographic protocols / Evolving Access Structure, Secret Sharing, Essential Participants, Information Theoretic

Original Publication (with minor differences): COMSYS 2020 (to appear)