Paper 2024/2019

Key-Insulated and Privacy-Preserving Signature Scheme with Publicly Derived Public Key, Revisited: Consistency, Outsider Strong Unforgeability, and Generic Construction

Abstract

Liu et al. (EuroS&P 2019) introduced Key-Insulated and Privacy-Preserving Signature Scheme with Publicly Derived Public Key (PDPKS) to enhance the security of stealth address and deterministic wallet. In this paper, we point out that the current security notions are insufficient in practice, and introduce a new security notion which we call consistency. Moreover, we explore the unforgeability to provide strong unforgeability for outsider which captures the situation that nobody, except the payer and the payee, can produce a valid signature. From the viewpoint of cryptocurrency functionality, it allows us to implement a refund functionality. Currently, basically there is no way to refund a coin when one mistakenly spends a coin to an address. This functionality rescues the case, even in the stealth environment that hides information of the payer. Note that the refund functionality only works before the payee transfers a coin to own wallet, and it prevents a double spending issue. Finally, we propose a generic construction of PDPKS that provides consistency and outsider strong unforgeability. The design is conceptually much simpler than known PDPKS constructions. It is particularly note that the underlying strongly unforgeable signature scheme is required to provide the strong conservative exclusive ownership (S-CEO) security (Cremers et al., IEEE S&P 2021). Since we explicitly require the underlying signature scheme to be S-CEO secure, our security proof introduces a new insight of exclusive ownership security which may be of independent interest.