  A privacy-preserving English auction protocol with round efficiency based on
a modified ring signature has been proposed in this paper. The proposed
protocol has three appealing characteristic: First, it offers conditional
privacy-preservation: on the one hand, the bidder is anonymous to the public,
on the other hand, only the collaboration of auctioneer and registration
manager can reveal the true identity of a malicious bidder. Second, it does not
require to maintain a black list which records the evicted malicious bidders.
Finally, it is efficient: it saves the communication round complexity comparing
with previously proposed solutions.
