It is often observed that agents tend to imitate the behavior of their neighbors in a social network. This imitating behavior might lead to the strategic decision of adopting a public behavior that differs from what the agent believes is the right one and this can subvert the behavior of the population as a whole.\ud \ud In this paper, we consider the case in which agents express preferences over two alternatives and model social pressure with the majority dynamics: at each step an agent is selected and its preference is replaced by the majority of the preferences of her neighbors. In case of a tie, the agent does not change her current preference. A profile of the agents’ preferences is stable if the each agent’s preference coincides with the preference of at least half of the neighbors (thus, the system is in equilibrium).\ud \ud We ask whether there are network topologies that are robust to social pressure. That is, we ask whether there are graphs in which the majority of preferences in an initial profile s always coincides with the majority of the preference in all stable profiles reachable from s. We completely characterize the graphs with this robustness property by showing that this is possible only if the graph has no edge or is a clique or very close to a clique. In other words, except for this handful of graphs, every graph admits at least one initial profile of preferences in which the majority dynamics can subvert the initial majority. We also show that deciding whether a graph admits a minority that becomes majority is NP-hard when the minority size is at most 1/4-th of the social network size
Abstract. Passwords and PINs are still the most deployed authentication mechanisms and their protection is a classical branch of research in computer security. Several password schemes, as well as more sophisticated tokens, algorithms, and protocols, have been proposed during the last years. Some proposals require dedicated devices, such as biometric sensors, whereas, others of them have high computational requirements. Graphical passwords are a promising research branch, but implementation of many proposed schemes often requires considerable resources (e.g., data storage, high quality displays) making difficult their usage on small devices, like old fashioned ATM terminals, smart cards and many low-price cellular phones.In this paper we present a graphical mechanism that handles authentication by means of a numerical PIN, that users have to type on the basis of a secret sequence of objects and a graphical challenge. The proposed scheme can be instantiated in a way to require low computation capabilities, making it also suitable for small devices with limited resources. We prove that our scheme is effective against "shoulder surfing" attacks.
Package management systems play an essential role in pursuing systems dependability by ensuring that software is correctly installed and kept up-to-date according to vendor-defined installation policies. Circumventing such policies could make the system unhealthy and insecure and can constitute a serious security threat. In many application scenarios, e.g., distribution of commercial software, the confidentiality of the software must be guaranteed against non-authorized players. In some cases, the installation policy itself is considered a sensitive information, e.g., when it reveals required hardware in military contexts. In this paper we address the problem of strongly enforcing software dependencies in package management systems, to prevent that a malicious user forces the system to install any package despite its requirements are not completely fulfilled. The enforcement is strong in the sense that the encrypted software package cannot be even decrypted if the dependencies are not satisfied. Once a new package is decrypted and installed, our protocol non-interactively updates the key material on the target device. This key update will allow the decryption of further packages that depend on the newly installed one. We further present “policy-hiding” variants of our protocol. Finally we provide an experimental evaluation of the system performance
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