We propose an electronic auction scheme satisfying that (i) a group of colluding bidders cannot control the contract price arbitrarily, (ii) all prices of bidders except the winner are never revealed to anyone (even to the auction house), and (iii) only the auction house recognizes the winner’s identity, while the other losers can verify the fact that the winner belongs to the advanced registered group. Our scheme does not rely on an anonymous channel nor a trusted third center. Our system can be implemented only with the public-key technology and cryptographic hash functions and all bidders can verify the validity of process for determining a winner via a public bulletin board. To achieve stronger anonymity of the winner, we develop a new variant of convertible undeniable group signatures. In our designed signature scheme, the convertibility has two phases: one is convertible from online to off-line in verification-stage, and the other is convertible from individual to group.