On the Security of O-PSI a Delegated Private Set Intersection on Outsourced Datasets

In recent years, determining the common information privately and efficiently between two mutually mistrusting parties have become an important issue in social networks. Many Private set intersection (PSI) protocols have been introduced to address this issue. By applying these protocols, two parties can compute the intersection between their sets without disclosing any information about components that are not in the intersection. Due to the broad range of computational resources that the cloud can provide for its users, determining the set intersection by cloud may decrease the computational cost of the users. The proposed protocol by Abadi et al. is one of the introduced protocols in this context. In this paper, we show that their protocol is vulnerable against man in the middle attack and the collusion between the cloud and one of the communicating parties. Also, a solution will be proposed to secure the protocol against mentioned attacks.