Research On Privacy Preserving Electronic Auction And Electronic Voting Protocol

Secure multi-party computation is a scenario that there are n participants P1,P2,..., Pn in untrustful multi-user network, Pi holds secret data xi and they wish to compute the function f(x1,x2,...,xn)==(y1,y2,...nyn) on the condition that Pi only obtains yi without disclosing xi to other participants. Secure multi-party computation is distributed protocols which can make users complete the computation and no more privacy is revealed.Electronic auction and electronic voting are typical application of secure multi-party computation. In order to preserve the privacy of participants, we need construct protocol with tools in cryptography to achieve the security and fairness in electronic auction and electronic voting. This thesis designs privacy preserving electronic auction and electronic voting protocols using secure multi-party techniques. The main innovations and research work can be summarized as follows:(1) Research on the architecture without trustful third party. Due to the existence of auctioneer, it is hard to avoid fraud and keep bid confidentiality in the traditional electronic auction system. Therefore, we model the auction settings and propos a new privacy preserving electronic auction system without auctioneers and its proxy model. Function of the modules in the system is also introduced. This architecture can be applied to solve the problem of privacy preserving in electronic voting model. Specifically, we study the channel model in the system. The bidders can make use of the subliminal channel to transfer secret messages. To avoid the conspiracy of bidders, we design a new ElGamal scheme of subliminal-freeness. The bidders should generate their signature with this scheme to eliminate the subliminal-freeness in the broadcast channel model.(2) Design privacy preserving electronic auction protocols. To deal with the popular mechanism, group-buying auction, a secure protocol without auctioneer in semi-honest model was presented. Taking advantage of the homomorphic lemma of distributed ElGamal scheme, the bidders can compute the result by themselves without disclosing own messages. The correctness and security are also analyzed. Then we extend the protocol and propose a basic problem in secure multiparty computation, secure zone distribution problem also with a general solution; we also present a secure protocol without auctioneer for (M+1)-st price auction. Taking advantage of the homomorphic lemma of threshold ElGamal encryption, the bidders can compute the result by themselves without leaking own messages. In the phase of opening bid, the offline of the unsuccessful bidder may cause the price can’t be calculated. This protocol can deal with the problem.(3) Design full privacy election voting protocol.The concept of "full privacy" in electronic voting was firstly proposed, not only the privacy of voters is concerned, but also the candidates’. The votes published in the tallying stage also impair candidates’privacy because of this information can be easily abused. A privacy preserving electronic election protocol without any trusted third party is provided for k-out-of-m election. It’s based on distributed ElGamal encryption and Mix-match technique. The voters can compute the result by themselves without disclosing their will and the vote of the losing candidates. Moreover, whether the vote of winner candidate is more than a half can be verified directly. This scheme satisfies "vote and go" pattern and achieves full privacy.