Christian Richthammer

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Online social networks (OSNs) have become an integral part of social interaction and communication between people. Reasons include the ubiquity of OSNs that is offered through mobile devices and the possibility to bridge spatial and temporal communication boundaries. However, several researchers have raised privacy concerns due to the large amount of user(More)
The growing relevance and usage intensity of Online Social Networks (OSNs) along with the accumulation of a large amount of user data has led to privacy concerns among researchers and end users. Despite a large body of research addressing OSN privacy issues, little differentiation of data types on social network sites is made and a generally accepted(More)
Currently, many users of Social Network Sites are insufficiently aware of who can see their shared personal items. Nonetheless, most approaches focus on enhancing privacy in Social Networks through improved privacy settings, neglecting the fact that privacy awareness is a prerequisite for privacy control. Social Network users first need to know about(More)
Reputation systems provide a valuable method to measure the trustworthiness of sellers or the quality of products in an e-commerce environment. Due to their economic importance, reputation systems are subject to many attacks. A common problem are unfair ratings which are used to unfairly increase or decrease the reputation of an entity. Although being of(More)
We are currently living in the age of Big Data coming along with the challenge to grasp the golden opportunities at hand. This mixed blessing also dominates the relation between Big Data and trust. On the one side, large amounts of trust-related data can be utilized to establish innovative data-driven approaches for reputation-based trust management. On the(More)
Reputation systems have been extensively explored in various disciplines and application areas. A problem in this context is that the computation engines applied by most reputation systems available are designed from scratch and rarely consider well established concepts and achievements made by others. Thus, approved models and promising approaches may get(More)
Security compliance has become an important topic for mediumand large-sized companies in the recent years. In order to fulfill all requirements legally imposed, high quality identity management – particularly with respect to correct and consistent access control – is essential. In this context, the concept of recertification has proven itself to maintain(More)
Attacks on trust and reputation systems (TRS) as well as defense strategies against certain attacks are the subject of many research papers. Although proposing valuable ideas, they all exhibit at least one of the following major shortcomings. Firstly, many researchers design defense mechanisms from scratch and without reusing approved ideas. Secondly, most(More)
Even though today’s recommender algorithms are highly sophisticated, they can hardly take into account the users’ situational needs. An obvious way to address this is to initially inquire the users’ momentary preferences, but the users’ inability to accurately state them upfront may lead to the loss of several good alternatives. Hence, this paper suggests(More)