In this paper we present the first framework that allows the creation of Secret Interest Groups (SIGs) in Online Social Networks; SIGs are self managed groups formed outside of the social network, around secret, sensitive or private topics. Members exchange credentials that can be used inside the social network to authenticate upon friendship requests or to secure user-generated content. To this end we present a set of cryptographic algorithms leveraging on well-studied primitives, and we describe a java implementation of the framework for Facebook. Categories and Subject Descriptors C.2.0 [Computer-Communication Networks]: General— Security and protection Keywords Social Networks, Secret Interest Groups, Secret Handshakes