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A private set membership (PSM) protocol allows a “receiver” to learn whether its input x is contained in a large database 𝖣𝖡 held by a “sender”. In this work, we define and construct credible private set membership (C-PSM) protocols: in addition to the conventional notions of privacy, C-PSM provides a soundness guarantee that it is hard for a sender (that does not know x) to convince the receiver that 𝑥∈𝖣𝖡. Furthermore, the communication complexity must be logarithmic in the size of 𝖣𝖡. We provide 2-round (i.e., round-optimal) C-PSM constructions based on standard assumptions: We present a black-box construction in the plain model based on DDH or LWE. Next, we consider protocols that support predicates f beyond string equality, i.e., the receiver can learn if there exists 𝑤∈𝖣𝖡 such that 𝑓(𝑥,𝑤)=1. We present two results with transparent setups: (1) A black-box protocol, based on DDH or LWE, for the class of NC1 functions f which are efficiently searchable. (2) An LWE-based construction for all bounded-depth circuits. The only non-black-box use of cryptography in this construction is through the bootstrapping procedure in fully homomorphic encryption. As an application, our protocols can be used to build enhanced round-optimal leaked password notification services, where unlike existing solutions, a dubious sender cannot fool a receiver into changing its password. https://doi.org/10.1007/978-3-031-31371-4_6 

We propose a novel system for creating data plugs and sockets for plug-and-play database web services. We adopt a plug-and-play approach to couple an application to a database. In our approach a designer constructs a “plug,” which is a simple specification of the output produced by the service. If the plug can be “played” on the database “socket” then the web service is generated. Our plug-and-play approach has three advantages. First, a plug is portable. A plug can be played on any data source to generate a web service. Second, a plug is reliable. The database is checked to ensure that the service can be safely and correctly generated. Third, plug-and-play web services are easier to code for complex data since a service designer can write a simple plug, abstracting away the data’s real complexity. We describe a system for plug-and-play web services and experimentally evaluate the system.