DyCAPS: Asynchronous Dynamic-committee Proactive Secret Sharing

Dynamic-committee proactive secret sharing (DPSS) enables the refresh of secret shares and the alternation of shareholders without changing the secret. Such a proactivization functionality makes DPSS a promising technology for long-term key management and committee governance. In non-asynchronous networks, CHURP (CCS '19) and COBRA (S&P'22) have achieved best-case square and cubic communication cost, respectively, w.r.t. the number of shareholders. However, the overhead of asynchronous DPSS remains high. In this paper, we fill this gap and propose DyCAPS, an efficient asynchronous DPSS protocol with a cubic communication cost. DyCAPS supports the transfer of both low- and high-threshold secret shares among dynamic committees with the same communication and computation complexity. Experimental results show that proactivization between two disjoint committees of 4 (resp., 64) members takes 1.3 (resp., 51) seconds.