Event Invitations in Privacy-Preserving DOSNs - Formalization and Protocol Design

Online Social Networks (OSNs) have an infamous history of privacy and security issues. One approach to avoid the massive collection of sensitive data of all users at a central point is a decentralized architecture. An event invitation feature – allowing a user to create an event and invite other users who then can confirm their attendance – is part of the standard functionality of OSNs. We formalize security and privacy properties of such a feature like allowing different types of information related to the event (e. g., how many people are invited/attending, who is invited/attending) to be shared with different groups of users (e. g., only invited/attending users). Implementing this feature in a Privacy-Preserving Decentralized Online Social Network is non-trivial because there is no fully trusted broker to guarantee fairness to all parties involved. We propose a secure decentralized protocol for implementing this feature, using tools such as storage location indirection, ciphertext inferences and a disclose-secret-ifcommitted mechanism, derived from standard cryptographic primitives. The results can be applied in the context of Privacy-Preserving DOSNs, but might also be useful in other domains that need mechanisms for cooperation and coordination, e. g., Collaborative Working Environment and the corresponding collaborative-specific tools, i. e., groupware, or Computer-Supported Collaborative Learning.