Secure Threshold Wallet Supporting Full Stealth Address

Since the emergence of Bitcoin, cryptocurrencies have attracted much attention. Digital wallets are a key component of cryptocurrency systems and provide convenient methods for users to store and manage keys. In particular, threshold wallets (ThW) enable distributed transaction authorization and have been studied in many practical scenarios. In addition to the secure authorization of transactions, cryptocurrencies also concern the user’s privacy. Among solutions to privacy, the stealth address (SA) method is preferred for its low cost and high compatibility with existing cryptocurrencies. Though transaction users may call threshold wallets and stealth address methods, respectively, there is no known research on their security once combined. This paper presents a formal study on the joint use of threshold wallets and stealth addresses, aiming at a scheme that enforces both security and privacy. To this end, we first reveal the problems that the direct combination poses, and then propose a novel paradigm, FSA-ThW, that maintains all the merits of threshold wallets and, moreover, realizes full stealth address under the threshold setting (we call this full unlinkability). Also, we provide a detailed construction with formal proof for FSA-ThW. We implement this construction, and our experimental results show that compared with the threshold wallet scheme without SA, FSA-ThW accomplishes the full stealth address with an extra cost of up to 7.5%∼8.7%.