Efficient Ring Signatures Without Random Oracles

We describe the first efficient ring signature scheme secure, without random oracles, basedon standard assumptions. Our ring signatures are based in bilinear groups. For l members ofa ring our signatures consist of 2l + 2 group elements and require 2l + 3 pairings to verify. Weprove our scheme secure in the strongest security model proposed by Bender, Katz, and Morselli:namely, we show our scheme to be anonymous against full key exposure and unforgeable withrespect to insider corruption. A shortcoming of our approach is that all the users’ keys must bedefined in the same group.