A Resilient and Energy-saving Incentive System for Resource Sharing in MANETs

Despite of all progress in terms of computational power, communication bandwidth, and feature richness, limited battery capacity is the major bottleneck for using the resources of mobile devices in innovative distributed applications. Incentives are required for motivating a user to spend energy on behalf of other users and it must be ensured that providing these incentives neither consumes much energy by itself nor allows for free-riding and other types of fraud. In this paper, we present a novel incentive system that is tailored to the application scenario of energyaware resource-sharing between mobile devices. The system has low energy consumption due to avoiding the use of public key cryptography. It uses a virtual currency with reusable coins and detects forgery and other fraud when cashing coins at an off-line broker. A prototype-based measurement study indicates the energy-efficiency of the system, while simulation studies show its resilience to fraud. Even in scenarios with 75% of fraudulent users that are colluding to disguise their fraud only 3.2% of them get away with it while the energy overhead (about 3%) for the incentive system is still moderat

Epidemic Dissemination of Presence Information in Mobile Instant Messaging Systems

This paper presents an approach for exchanging presence information between users of an instant messaging system in a mobile ad hoc network. As major feature, presence information is transferred when mobile users get in direct contact, similar to the spread of an infections disease. By exploiting node mobility, presence information is epidemically distributed throughout the network, effectively overcoming network partitions. We show how to apply the Passive Distributed Indexing Protocol, which implements a general-purpose lookup service for mobile applications building upon epidemic data dissemination, for implementing the exchange of presence information. The effectiveness of the approach is illustrated in a simulation study using the network simulator ns-2. Building upon the results, we present the architecture of a mobile instant messaging system that supports the widely adopted Extensible Messaging and Presence Protocol (XMPP), an IETF standardized protocol for instant messaging

Privacy-Preserving and Scalable Authentication based on Network Connection Traces

Since password-based authentication is no longer sufficient for web applications, additional authentication factors are required. Especially in the context of mobile devices and with regard to usability, there is an increasing focus on methods where the user's behavior is used as authentication factor (e.g., touchscreen interactions or sensors). As this typically requires the processing of large amounts of sensitive data, issues related to privacy and scalability arise. Our work addresses the issues by presenting a scalable and privacy-friendly approach for authenticating users of mobile applications based on information about their network connections

Effective Dissemination of Presence Information in Highly Partitioned Mobile Ad Hoc Networks

Presence technology enables users of an instant messaging (IM) system to determine if their contacts are online and ready to communicate. In this paper, we propose an effective approach for the proactive dissemination of frequently changing presence information in highly partitioned mobile, wireless networks with IEEE 802.11 technology. Although communication techniques for intermittently connected networks have been extensively studied in the field of delay tolerant networking, the fact that presence information is highly delay sensitive requires a thorough revision of these techniques. To this end, we use discrete-event simulation based on a high-level stochastic model of the IM system to compare different approaches for disseminating presence information in terms of sustained consistency (i.e., fraction of time presence information is in a coherent state) and traffic requirements. Building upon the outcome of the simulation study, we propose the system for presence information exchange by epidemic dissemination (SPEED). Results of a detailed ns-2 simulation study show that SPEED outperforms an approach based on optimized flooding by up to 20% in terms of sustained consistency for low node density and saves up to 48% of control traffic for medium to high node density

Exploiting epidemic data dissemination for consistent lookup operations in mobile applications

This paper presents a general-purpose distributed lookup service, denoted Passive Distributed Indexing (PDI). PDI stores entries in form of (key, value) pairs in index caches located at mobile devices. Index caches are filled by epidemic dissemination of popular index entries. By exploiting node mobility, PDI can resolve most queries locally without sending messages outside the radio coverage of the inquiring node. For keeping index caches coherent, configurable value timeouts implementing implicit invalidation and lazy invalidation caches implementing explicit invalidation are introduced. Inconsistency in index caches due to weak connectivity or node failure is handled by value timeouts. Lazy invalidation caches reduce the fraction of stale index entries due to modified data at the origin node. Similar to index caches, invalidation caches are filled by epidemic distributions of invalidation messages. We evaluate the performance of PDI for a mobile P2P file sharing a mobile instant messaging application. Simulation results show that with the suitable integration of both invalidation mechanisms, up to 80% of the lookup operations return correct results and more than 90% of results delivered by PDI index caches are up-to-date

Consistency mechanisms for a distributed lookup service supporting mobile applications

This paper presents a general-purpose distributed lookup service, denoted Passive Distributed Indexing (PDI). PDI stores entries in form of (key, value) pairs in index caches located in each mobile device. Index caches are filled by epidemic dissemination of popular index entries. By exploiting node mobility, PDI can resolve most queries locally without sending messages outside the radio coverage of the inquiring node. Thus, PDI reduces network traffic for the resolution of keys to values. For keeping index caches coherent, configurable value timeouts implementing implicit invalidation and lazy invalidation caches implementing explicit invalidation are introduced. Inconsistency in index caches due to weak connectivity or node failure is handled by value timeouts. Lazy invalidation caches reduce the fraction of stale index entries due to modified data at the origin node. Similar to index caches, invalidation caches are filled by epidemic distributions of invalidation messages. Simulation results show that with the suitable integration of both invalidation mechanisms, more than 95% of results delivered by PDI index caches are up-to-date for the considered scenario

mPSAuth: Privacy-Preserving and Scalable Authentication for Mobile Web Applications

As nowadays most web application requests originate from mobile devices, authentication of mobile users is essential in terms of security considerations. To this end, recent approaches rely on machine learning techniques to analyze various aspects of user behavior as a basis for authentication decisions. These approaches face two challenges: first, examining behavioral data raises significant privacy concerns, and second, approaches must scale to support a large number of users. Existing approaches do not address these challenges sufficiently. We propose mPSAuth, an approach for continuously tracking various data sources reflecting user behavior (e.g., touchscreen interactions, sensor data) and estimating the likelihood of the current user being legitimate based on machine learning techniques. With mPSAuth, both the authentication protocol and the machine learning models operate on homomorphically encrypted data to ensure the users' privacy. Furthermore, the number of machine learning models used by mPSAuth is independent of the number of users, thus providing adequate scalability. In an extensive evaluation based on real-world data from a mobile application, we illustrate that mPSAuth can provide high accuracy with low encryption and communication overhead, while the effort for the inference is increased to a tolerable extent.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

Relating Query Popularity and File Replication in the Gnutella Peer-to-Peer Network

In this paper, we characterize the user behavior in a peer-to-peer (P2P) file sharing network. Our characterization is based on the results of an extensive passive measurement study of the messages exchanged in the Gnutella P2P file sharing system. Using the data recorded during this measurement study, we analyze which queries a user issues and which files a user shares. The investigation of users queries leads to the characterization of query popularity. Furthermore, the analysis of the files shared by the users leads to a characterization of file replication. As major contribution, we relate query popularity and file replication by an analytical formula characterizing the matching of files to queries. The analytical formula defines a matching probability for each pair of query and file, which depends on the rank of the query with respect query popularity, but is independent of the rank of the file with respect to file replication. We validate this model by conducting a detailed simulation study of a Gnutella-style overlay network and comparing simulation results to the results obtained from the measurement

Peer-to-Peer-Systeme für drahtlose Multihop-Netze

Im Bereich der Zugangsnetze werden zukünftig drahtlose Multihop-Erweiterungen des Internets durch mobile Ad-hoc-Netze sowie durch drahtlose vermaschte Netze (sog. Wireless Mesh Networks) Verbreitung finden, da diese Netztechnologien den Datentransfer einfacher und schneller, womöglich auch deutlich kostengünstiger, durchführen können als zellulare Mobilfunknetze