Recipient Privacy in Online Social Networks

Alongside the intensive growth of Online Social Networks (OSNs), privacy has become an important concept and requirement when sharing content online, leading users to enforce privacy often using encryption when sharing content with multiple recipients. Although cryptographic systems achieve common privacy goals such as confidentiality, key privacy, and recipient privacy, they have not been designed aiming at dynamic types of networks. In fact, the interactive nature of OSNs provides adversaries new attack vectors against privacy, and in particular against recipient privacy. We present the notion of frientropy, and argue that privacy of recipients is maintained in OSNs provided that the social graph has a high frientropy, besides the conventional recipient privacy notion. We compute the frientropy for various theoretical settings, and discuss its implications on some practical settings.