## 1 Introduction  
The ubiquitous prevalence of Social Networks (SNs) in modern societies, which consist of the most preferable cloud computing services worldwide, has dynamically transformated not only the field of communication, but also many others socio-economical domains, such as relationships maintenance, entertainment, social interaction, self-representation, professional activities, and e-goverance [1]. This intensification of individual and social activities, in several domains within SNs, promotes complexity and it shifts the edges among the determination and the activities of public and private life [2]. This occurs, since, in order for SNs to be effectively utilized, users provide a great amount of personal information, which is further analyzed and used by the SNs providers [3]. Furthermore, taking into consideration that SNs overcome spatiotemporal boundaries as well, they lead to a greater diffusion of users' personal and sensitive information than other informational systems [4]. As [5] maintain this ubiquity of information analyses and distribution impactson users' social norms of privacy. In this respect, [6] emphatically supports that a new battleground among individuals and service providers is indicated, concerning \"a new kind of information war\" p. 64, regarding the access, collection, storage, processing and disclosure of users' personal information. SNs' structure challenge the concept of privacy [7; 8; 9], which, over the past years, has been determined under different, but often overlapping frameworks and notions [10; 11]. Therefore, they challenge users' social privacy norms and their respective practices. Thus, under this \"war\" and the privacy notion challenges, it has been recognized that users' privacy protection is not adequately achieved within SNs. Furthermore, users' complex privacy concerns and needs, under the different contexts that they use SNs, are not respectively well-considered [12]. Additionally, despite the fact that several privacy and security measures have been introduced by SNs providers in order to provide users' with the sense that they have control over their information, it is proved that only providers have this ability [13]. Previous research has also highlighted that users differ significantly in their privacy management strategies within SNs, raising questions for how to support such broad privacy concerns and needs in a more user-centered way. In particular, in Europe, this is even more immense, considering the enforcement of the General Data Protection Regulation (GDPR), which promotes users' privacy safeguard not only at a socio-legal oriented layer, but also at a technical one, supporting the implementation of the principle of Privacy by Design (PbD). PbD, introduced at first by [14], aims to be a holistic and human-orientated approach for implementing technical privacy measures, offering realistic solutions [15]. According to GDPR, the data controllers and processors, including SNs providers obviously, are obligated to deploy the appropriate technical procedures in order to ensure the protection of the data subjects' rights [16]. In this regard, providing SNs users with the control over their information could be a realistic solution to several privacy issues that derive from users' willing to disclose information, while preventing unauthorized access from third parties. From a technical perspective, as [13] supports, either hosting user's information on a constantly available paid server or providing personal server for each user or a personal virtual machine in a paid cloud, as well as the acting of personal mobile devices with Internet connectivity as servers, could be effective solutions for users' privacy protection. To that end and towards to provide effective privacy protection schemes within SNs, in a more user-centered way, several self-adaptive privacy approaches have been developed [17].