A Not-So-Trival Replay Attack Against DH-PSI
In this note, we present a simple yet effective inter-session replay attack against the Diffie-Hellman style private set intersection protocol (cf. [Mea86]). The attack is indistinguishable from ordinary protocol execution, and yet allows the attacker to learn the cardinality of the intersection of honest party’s input sets. This kind of attack demonstrates the inadequacy of semi-honest security guarantee when facing more serious adversarial threats, and highlights the necessity for security augmentation of protocols derived from [Mea86].