CertainTrust - A Robust Bayesian Trust Model for Humans and Agents

In the vision of ubiquitous computing, the activities of daily life are supported by a multitude of heterogeneous, loosely coupled computing devices. The support of seamless collaboration between users, as well as between their devices, can be seen as one of the key challenges for this vision to come true.

This project provides a trust based approach to supporting the selection of trustworthy interaction partners. The goal of this approach is to estimate an entity's trustworthiness as accurately as possible in order to improve the average quality of the entity's interactions. An online demonstrator is available here.


Details see <a href=http://portal.acm.org/citation.cfm?id=1529573>here</a>.

In this project, the trustworthiness of an entity is derived from evidence gained during past interactions. To this end, current Bayesian trust models are extended and improved regarding the following aspects:


  1. better integration of the characteristics of the application context,
  2. more intuitive access to the trust model, and
  3. better integration of recommendations by third parties.

The last aspect is important as there are numerous situations in which direct evidence between entities is rare. The proposed approach provides means for the robust integration of recommendations provided by third parties, especially considering attacks by entities intentionally providing misleading recommendations.


The scientific contribution of this thesis is summarized as follows:


  • The trust model that is provided in this thesis extends Bayesian trust models in order to improve the integration of context-dependent parameters, such as dispositional trust and aging of evidence. Furthermore, a parameter called maximum number of evidenceunits allows the user to define the number of evidence that is expected to be sufficient for being representative for an entity's behavior within a certain application context. In the proposed model, the dispositional trust can be assessed according to the preference of the user; alternatively, a new approach for deriving the dispositional trust from the behavior of previously encountered entities is provided.
  • The proposed interrelation between the aging and the maximum number of expected evidence units allows the limitations of current Bayesian trust models to be overcome. The thesis shows that in those models, aging either does not have an impact on the expectation value in the absence of evidence, or it narrows the range of the expectation value.
  • A second representation of trust - called the Human Trust Interface (HTI) - is proposed providing for an easier access to the model by human users. This representation is based on a simple set of parameters. These parameters are also the basis for a graphical representation allowing users to interpret and adjust the trust values of other entities intuitively.
  • As the model supports two different representations a mapping between both representations is required in order to switch between both representations. The provided mapping allows users and developers of trust models to benefit from the advantages of both representations.
  • The distributed computational model that is proposed for the aggregation of direct evidence and recommendations has been designed to be especially robust to so-called Sybil attacks, which occur when a single party tries to multiply the influence of its recommendations by creating a high number of seemingly independent entities. This is achieved using the accuracy of a recommender's past recommendations as well as the rank of the recommender in order to limit a recommender's influence. Especially, considering the rank of a recommender, i.e., its position in the group of recommenders, provides a means for limiting the influence of a potentially infinite number of malicious recommenders under certain circumstances.


The trust model has been evaluated in two user studies which support that users feel comfortable with the proposed graphical representation. Furthermore, in the simulation of collaboration in an opportunistic network, the model shows a good performance regarding the estimation of an entity's trustworthiness and regarding the average quality of interactions when using the trust model to find the best interaction partner. This results from the comparison to a state-of-the-art approach, as well as from a comparison to an artificial model that is initialized with the system variables of the simulation model, and therefore serves as perfect selection strategy. The simulation shows the results of the different approaches over a set of 15 populations, which have been canonically derived from the system model, modeling entities with different typical behaviors.


Former Project Members

  • Dr. Sebastian Ries


Key Publications

  • Ries, S., Trust in Ubiquitous Computing, PhD thesis, Technische Universität Darmstadt, 2009. (online available)
  • Ries, S., Extending Bayesian Trust Models Regarding Context-Dependence and User Friendly Representation, Proceedings of the 2009 ACM Symposium on Applied Computing, ACM Press, 2009.
  • Ries, S. & Aitenbichler, E., Limiting Sybil Attacks on Bayesian Trust Models in Open SOA Environments, Proceedings of the The First International Symposium on Cyber-Physical Intelligence (CPI-09), 2009.
  • Ries, S. & Heinemann, A., Analyzing the Robustness of CertainTrust, 2nd Joint iTrust and PST Conference on Privacy, Trust Management and Security, Springer, 2008.
  • Ries, S., CertainTrust: A Trust Model For Users And Agents, Proceedings of the 2007 ACM Symposium on Applied Computing, ACM Press, 2007.

News SST


Telecooperation Lab is co-organizing the “Security & Privacy Week” 2016

The Technical University of Darmstadt is organizing the “Security & Privacy Week (SPW2016)”, July 18 – 22 2016 in Darmstadt, Germany. [more]

Category: Allgemeine News, Forschung


Full paper accepted at ISGT 2015

The paper on  "Efficient, Verifiable, Secure, and Privacy-Friendly Computations for the Smart Grid" by Fábio Borges, Florian Volk, and Max Mühlhäuser was accepted in the Sixth Conference on... [more]


Introducing Asymmetric DC-Nets

The short paper on "Introducing Asymmetric DC-Nets" by Fábio Borges, Johannes Buchmann, and Max Mühlhäuser was accepted in the IEEE Conference on Communications and Network Security (CNS). The... [more]

Category: Allgemeine News


Making the Most of Customer Product Reviews accepted at CENTRIC 2014

The paper "Making the Most of Customer Product Reviews" by Florian Volk, Janette Pitzschel, and Max Mühlhäuser was accepted at the 7th International Conference on Advances in Human-oriented and Personalized Mechanisms,... [more]

Category: Allgemeine News


Modeling Degrees of Fairness for Collaborations accepted at NOPE 2014

The paper "Modeling Degrees of Fairness for Collaborations" by Florian Volk, Maria Pelevina, Sheikh Mahbub Habib, Sascha Hauke, and Max Mühlhäuser was accepted at the 2nd IEEE International Workshop on Network... [more]

Category: Allgemeine News


Journal Article Accepted

The paper on  "EPPP4SMS: Efficient Privacy-Preserving Protocol for Smart Metering Systems and Its Simulation Using Real-World Data" by Fábio Borges and Max Mühlhäuser was accepted to be published in IEEE... [more]

Category: Allgemeine News


Full paper accepted at IEEE CNS 2014

The paper on "iKUP Keeps Users' Privacy in the Smart Grid" by Fábio Borges and Leonardo A. Martucci was accepted in the IEEE Conference on Communications and Network Security (CNS). The conference will take place... [more]

Category: Allgemeine News

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