  Truthful spectrum auction is believed to be an effective method for spectrum
redistribution. However, privacy concerns have largely hampered the practical
applications of truthful spectrum auctions. In this paper, to make the
applications of double spectrum auctions practical, we present a
privacy-preserving and socially efficient double spectrum auction design, SDSA.
Specifically, by combining three security techniques: homomorphic encryption,
secret sharing and garbled circuits, we design a secure two-party protocol
computing a socially efficient double spectrum auction, TDSA, without leaking
any information about sellers' requests or buyers' bids beyond the auction
outcome. We give the formal security definition in our context, and
theoretically prove the security that our design achieves. Experimental results
show that our design is also efficient in performance, even for large-scale
double spectrum auctions.
