Paper 2008/045

Threshold RSA for Dynamic and Ad-Hoc Groups

Rosario Gennaro, Shai Halevi, Hugo Krawczyk, and Tal Rabin

Abstract

We consider the use of threshold signatures in ad-hoc and dynamic groups such as MANETs ("mobile ad-hoc networks"). While the known threshold RSA signature schemes have several properties that make them good candidates for deployment in these scenarios, we show that none of these schemes is practical enough for realistic use in these highly-constrained environments. In particular, this is the case of the most efficient of these threshold RSA schemes, namely, the one due to Shoup. Our contribution is in presenting variants of Shoup's protocol that overcome the limitations that make the original protocol unsuitable for dynamic groups. The resultant schemes provide the efficiency and flexibility needed in ad-hoc groups, and add the capability of incorporating new members (share-holders) to the group of potential signers without relying on central authorities. Namely, any threshold of existing members can cooperate to add a new member. The schemes are efficient, fully non-interactive and do not assume broadcast.