People suffer from information overload while using digital devices, yet little is known about the interaction of the overload experiences and everyday web behavior. We conducted a large-scale longitudinal observational study (N=277) over seven months. The study combines over 13M passively observed web traces from desktop computers and mobile devices with four waves of surveys measuring the experienced information overload. Our results demonstrate that repetitive, short-duration use of devices (i.e., high sparseness) in online sessions differentiate highly overloaded individuals from others with a large effect. Furthermore, mobile web duration and session sparseness predict increase in the overload. Overall, our results highlight that the web usage duration, the temporal patterns of usage, and the choice of a device are associated with information overload. By highlighting session sparseness as an actionable behavioral signal, our results inform the development of digital well-being tools that nudge users toward healthier interaction patterns and reduce overload.

One central goal of game designers is to make games that resonate with players. Yet, within HCI games research, resonance is used vaguely as an everyday notion. In this work, we draw on psychological research on resonance to conduct a qualitative survey (n = 110) to explore how players characterize game experiences that resonated with them, to deliminate what resonance means for players and the interactive medium of games. Our findings illustrate how resonance captures the feeling of gameplay encounters that go on to have profound and long-lasting emotional and cognitive impacts. Our findings outline resonance as an underlying experiential quality relevant to various existing PX conceptualizations, such as eudaimonia, meaningfulness, reflection, emotional challenge, game feel, and perspective or behavioral change. Based on our findings, we outline resonance as a useful explanatory concept for what makes videogame experiences emotional, meaningful, moving, and even transformative experiences.

Everyone needs to somehow manage personal information, and there are numerous choices for technologies that support personal information management (PIM). Meanwhile, many suffer from experiences of information overload related to PIM. We developed a quantitative model of information overload in PIM and tested it against data we collected in a large-scale survey study (N = 1,011). Using structural equation modeling, we found that using many PIM technologies accounts for information overload through practices of keeping information and feeling of desperation, and through organizing and feeling of efficacy, but not directly. Our study deepens the understanding of information overload in the context of PIM and distinguishes different roles that technologies, practices, and affects have in relation to it. The findings highlight how designs and interventions targeted to reduce negative affects related to PIM could be the most effective in countering information overload.

GPTs are customized LLM apps built on OpenAI's large language model.Any individual or organization can use and create GPTs without needing programming skills.However, the rapid proliferation of over three million GPTs has raised signifcant privacy concerns.To explore the privacy perspectives of users and creators, we interviewed 23 GPT users with varying levels of creation experience.Our fndings reveal blurred lines between user and creator roles and their understanding of GPT data fows.Participants raised concerns about data handling during collection, processing, and dissemination, alongside the lack of privacy regulations.Creators also worried about loss of their proprietary knowledge.In response, participants adopted practices like self-censoring input, evaluating GPT actions, and minimizing usage traces.Focusing on the dual role of user-creators, we fnd that expertise and responsibility shape privacy perceptions.Based on these insights, we propose practical recommendations to improve data transparency and platform regulations.

Entertainment videogames have been recognized for their potential therapeutic benefits, but there is a need for more in-depth, game-specific explorations of the game features that could contribute to such benefits. This study examines how players of Dark Souls describe the game as helping them cope with depression. We conducted a thematic analysis of Reddit discussions where players narrate their mental health experiences with the game, using AI tools to assist in identifying relevant data for a purposive sample. Our findings suggest that Dark Souls could support players’ mental health, for example, by (1) cultivating resilience and perseverance through its challenging gameplay, (2) triggering existential reflections through symbolic representations of depression, and (3) enabling supportive online communities and interactions. Our findings offer rich, player-centered insights into the perceived mental health benefits of commercial videogames, highlighting their potential to transcend entertainment and inform the design of engaging digital mental health tools.

People often use multiple communication apps concurrently for messaging, yet how they use these channels together and the motivations for switching between them remain underexplored. To investigate this, we conducted a two-week diary study followed by interviews (N=17), examining channel-switching practices and the management of social boundaries. Our findings reveal that users switch between multiple communication channels with the same contacts, driven by factors such as different topics, expectations for fast or slow communication rhythm, specific features suited to the situation, and app-specific vibes that match their mood at the moment. Additionally, we identify inertia, where users tend to stay on the app where the last interaction occurred, as the opposite of active channel switching. Our findings show that users do not actively distinguish apps based on relationships. Instead, their contacts are dispersed across different communication apps due to adaptive behaviors. These behaviors include users continually adapting to unique relationships, evolving communication needs, and app changes over time. Based on these insights, we propose design implications for multichannel communication to help users manage cross-app communication flows effectively.

Households increasingly play and engage with video games. We examined how households play video games among 20 interviewees coming from varied and familial households. Our study focused on interactions, examining how gaming influences daily household dynamics. Previous studies have focused mainly on the impact on relationships. Looking at households led us to observe fluid role dynamics around gaming. Our findings map the stages of how households play games from gaining plausible momentum, actions, conversations, and roles taken during game sessions, and reflections after gaming. Our findings highlight a novel role of the Gamer Host leading the game session and attending to everyone's enjoyment. Our observations exemplify the supportive and positive social outcomes close-knit gaming can afford and implications for achieving harmonious gaming in households. Our findings tie to prospects on communal and social aspects on technology use providing new perspectives on user experiences in an immediate social environment.

Collaborative family apps are designed for families to stay connected, look after their kids, and share life events. Despite their well-intended design, collaborative family apps can be invasive, leading to tensions in family relationships and exposure to online risks. We compared frequently downloaded collaborative family and parental control apps in terms of their features, with a focus on Apple's Family Sharing and Google's Family Link. We then conducted a qualitative interview study (N=20) to explore privacy experiences when using Apple's Family Sharing. Our results highlight privacy challenges with the use of collaborative family apps to negotiate boundaries and manage content, such as mismanaging finances and accidental content sharing. We reveal that roles and hierarchies on the app are unclear, leading to users' confusion about the privacy controls associated with each role. Based on these insights, we propose design recommendations to address these challenges and enhance the usability and privacy of collaborative family apps.

Users need to configure default apps when they first start using their devices. The privacy configurations of these apps do not always match what users think they have initially enabled. We first explored the privacy configurations of eight default apps Safari, Siri, Family Sharing, iMessage, FaceTime, Location Services, Find My, and Touch ID. We discovered serious issues with the documentation of these apps. Based on this, we studied users’ experiences with an interview study (N=15). We show that: the instructions for setting privacy configurations of default apps are vague and lack required steps; users were unable to disable default apps from accessing their personal information; users assumed they were being tracked by some default apps; default apps may cause tensions in family relationships because of information sharing. Our results illuminate on the privacy and security implications of configuring the privacy of default apps and how users understand the mobile ecosystem.

Videogames can transform the perspectives and attitudes of players. Prior discussion on this transformative potential has typically been limited to non-entertainment videogames with explicit transformational goals. However, recreational gaming appears to hold considerable potential for igniting deeply personal experiences of profound transformation in players. Towards understanding this phenomenon, we conducted an explorative autoethnographic study. For this, the first author played five narrative-driven videogames while collecting self-observational and self-reflective data of his experience during and outside gameplay. Our findings offer intimate insights into the trajectory and emotional qualities of personally meaningful and transformative videogame experiences. For example, we found that gameplay experiences that were initially perceived as bewildering or disorienting could evolve into more harmonious experiences laden with personal meaning. This shift in experience developed through different forms of subsequent re-engagement with initially discrepant game encounters.

Mysteries are an engaging form of fiction, capturing audiences with curiosity, uncertainty, and ambiguity. However, mysteries in games have presented a challenge for research since the word mystery may be understood as 1) detective mysteries with clear-cut answers or 2) as mysteries which are unsolvable and incomprehensible. This paper focuses on the latter kind of mysteries. To investigate what constitutes a mystery player experience, in what ways mystery games provide answers to players and how to design these games, we inspected five mystery games through a formalist game analysis by a player-researcher. We discovered (1) how the mystery player experience was characterised by enjoyment of irresolution, state of not receiving clear-cut answers to a mystery, (2) how a mystery condition, a state of wonder and fascination, promoted openness, and (3) how interpretation management represented the doing in the mystery player experience. To our surprise, although the player was driven to find answers to mysteries, the eventual irresolution was an enjoyable experience to the player. We conclude that all mysteries need not be answered during the game, and the experience can be enjoyable because of this.

In highly developed countries where smartphones are both accessible and expected, why are some individuals still choosing to use dumbphones? Dumbphones, as an anachronistic (or, outdated) technology are an unusual choice when many government systems, business services, and interpersonal relationships make use of the diverse communication methods presented by smartphones. However, dumbphones are increasingly (re)adopted by individuals seeking, among other motivations, a low-distraction digital handset. We investigate the phenomenon of designer dumbphones, or newly developed dumbphones redesigned to meet the needs of dumbphone users, despite dumbphone-unfriendly current technical infrastructural. We report on the results of interviews with eight traditional dumbphone users, five designer dumbphone users, and two designer dumbphone developers. Our findings highlight both the impact of the digital disconnection movement and dumbphones as tools for mental and physical health, practicing religious devotion, and enacting political disaffiliation. Our analysis takes into account experiences of isolation during the COVID-19 pandemic, and the kinds of privilege needed to choose digital disconnection, along with the interpersonal complications that result from doing so. This work contributes to conversations around volitional technical (non)use and disputes the notion that increased communication leads to richer interpersonal interaction. As dumbphone (re)adoption begins to trend in popular media, our goal is to uncover potential sites of digital disconnection and understand how different groups of individuals might experience those sites.

In this paper, we investigate browsing clutter, which refers to cluttered experiences of users due to buildup of disorganized browser elements and information. We studied what users experience as clutter, what behaviors and factors contribute to the clutter, and what users do when they experience clutter through an interview study (N = 16) and an online survey study (N = 400). Based on our studies, browsing clutter includes the amount of tabs and windows, content of the web pages and interactive elements, navigation, and search process. We identified sources of browsing clutter from task characteristics, such as importance and complexity, to user habits, such as multitasking and tab closing. To reveal the dynamics of browsing clutter, we modeled how browsing clutter is predicted by specific browsing habits and coping strategies. Our model demonstrates how individual forms of clutter are interrelated and altered by behavior. We discuss how browsing clutter relates to information overload.

Online games engage players in sharing their personal data with the games themselves and other players, which can pose security, privacy, and integrity risks to players. This paper presents an analysis of data practices in 21 online games and a qualitative interview study (N=20) that explores players' views on sharing their data in online games. Our results show that players' willingness to share personal information is contextual and related to game settings and game design elements. Our findings also highlight players' misconceptions and concerns surrounding data collection in games, and approaches to mitigate these concerns. Finally, this work identifies questionable design practices with online games and suggests design implications that will increase transparency and player control over data sharing.

The COVID-19 pandemic has led governments worldwide to introduce various measures restricting human activity and mobility. Along with the administration of COVID-19 vaccinations and rapid testing, socio-technological solutions such as digital COVID-19 certificates have been considered as a strategy to lessen these restrictions and allow the resumption of routine activities. Using a mixed-methods approach – a survey (n=1008) and 27 semi-structured interviews – this study explores the attitudes of residents in the Republic of Ireland towards the idea of introducing digital COVID-19 certificates. We examine the topics of acceptability, fairness, security and privacy of COVID-related personal data, and practical considerations for implementation. Our study reveals the conditional and contextual nature of the acceptability of digital certificates, identifying specific factors that affect it, associated data practices, and related public concerns and expectations of such technologies.

Gestures have recently gained interest as a secure and usable authentication method for mobile devices. Gesture authentication relies on recognition, wherein raw data is collected from user input and preprocessed into a more manageable form before applying recognition algorithms. Preprocessing is done to improve recognition accuracy, but little work has been done in justifying its effects on authentication. We examined the effects of three variables: location, rotation, and scale, on authentication accuracy. We found that an authentication-optimal combination (location invariant, scale variant, and rotation variant) can reduce the error rate by 45.3% on average compared to the recognition-optimal combination (all invariant). We analyzed 13 gesture recognizers and evaluated them with three criteria: authentication accuracy, and resistance against both brute-force and imitation attacks. Our novel multi-expert method (Garda) achieved the lowest error rate (0.015) in authentication accuracy, the lowest error rate (0.040) under imitation attacks, and resisted all brute-force attacks.

Smartphones frequently notify users about newly available messages or other notifications. It can be very disruptive when these notifications interrupt users while they are busy. Our work here is based on the observation that people usually exhibit different levels of busyness at different contexts. This means that classifying users' interruptibility as a binary status, interruptible or not interruptible, is not sufficient to accurately measure their availability towards smartphone interruptions. In this paper, we propose, implement and evaluate a two-stage hierarchical model to predict people's interruptibility intensity. Our work is the first to introduce personality traits into interruptibility prediction model, and we found that personality data improves the prediction significantly. Our model bootstraps the prediction with similar people's data, and provides a good initial prediction for users whose individual models have not been trained on their own data yet. Overall prediction accuracy of our model can reach 66.1%.

Energy-efficient localization is increasingly important for many types of smartphone apps. The research community has argued that fixed duty cycling of GPS is not a good choice for trajectory-based services concerning route accuracy. In this paper, we describe the design and implementation of a highly accurate map matching and path construction algorithm. Furthermore, with thorough field experiments, we show that fixed duty cycling of a smartphone GPS receiver is a feasible approach for trajectory-based services, and it can achieve considerable energy conservation without sacrificing much route accuracy. When increasing the GPS sampling period beyond 120 seconds, it saves at least 78% energy in comparison to continuous GPS sampling, while the loss of route accuracy tends to be stable around 23%.

Conventionally, the route recommendations given by GPS navigation applications have been considered as the optimal route search problem only between two locations - origin and destination [1]. Sometimes people want to visit several intermediate locations prior to reaching their final destination. For example, travelers may want to visit a diner and a gas station before arriving at their vacation destination. Although there is likely to be many choices that are available along the route to the destination, only one place from each type should be chosen. Furthermore, in new emerging application domains, such as “physical-world crowdsourcing” [2], people may want to opportunistically visit some places in order to complete personal or work related tasks. Our work explores a design space where we try to reduce the amount of requests made to third-party map and route data providers. We explore the simple idea of using the Euclidean distance as a rough estimate for the optimal route between destinations with multiple waypoints. Our preliminary results indicate that with over 80% of test cases, this simple Euclidean distance estimator approach gives at least one optimal routing alternative.

Digital currencies represent a new method for exchange -- a payment method with no physical form, made real by the Internet. This new type of currency was created to ease online transactions and to provide greater convenience in making payments. However, a critical component of a monetary system is the people who use it. Acknowledging this, we present results of our interview study (N=20) with two groups of participants (users and non-users) about how they perceive the most popular digital currency, Bitcoin. Our results reveal: non-users mistakenly believe they are incapable of using Bitcoin, users are not well-versed in how the protocol functions, they have misconceptions about the privacy of transactions, and that Bitcoin satisfies properties of ideal payment systems as defined by our participants. Our results illustrate Bitcoin's tradeoffs, its uses, and barriers to entry.

Free-form gesture passwords have been introduced as an alternative mobile authentication method. Text passwords are not very suitable for mobile interaction, and methods such as PINs and grid patterns sacrifice security over usability. However, little is known about how free-form gestures perform in the wild. We present the first field study (N=91) of mobile authentication using free-form gestures, with text passwords as a baseline. Our study leveraged Experience Sampling Methodology to increase ecological validity while maintaining control of the experiment. We found that, with gesture passwords, participants generated new passwords and authenticated faster with comparable memorability while being more willing to retry. Our analysis of the gesture password dataset indicated biases in user-chosen distribution tending towards common shapes. Our findings provide useful insights towards understanding mobile device authentication and gesture-based authentication.

In this paper, we present the design, implementation and evaluation of a user authentication system, Headbanger, for smart head-worn devices, through monitoring the user's unique head-movement patterns in response to an external audio stimulus. Compared to today's solutions, which primarily rely on indirect authentication mechanisms via the user's smartphone, thus cumbersome and susceptible to adversary intrusions, the proposed head-movement based authentication provides an accurate, robust, light-weight and convenient solution. Through extensive experimental evaluation with 95 participants, we show that our mechanism can accurately authenticate users with an average true acceptance rate of 95.57% while keeping the average false acceptance rate of 4.43%. We also show that even simple head-movement patterns are robust against imitation attacks. Finally, we demonstrate our authentication algorithm is rather light-weight: the overall processing latency on Google Glass is around 1.9 seconds.

Smartphone users do not fully know what their apps do. For example, an applications' network usage and underlying security configuration is invisible to users. In this paper we introduce Securacy, a mobile app that explores users' privacy and security concerns with Android apps. Securacy takes a reactive, personalized approach, highlighting app permission settings that the user has previously stated are concerning, and provides feedback on the use of secure and insecure network communication for each app. We began our design of Securacy by conducting a literature review and in-depth interviews with 30 participants to understand their concerns. We used this knowledge to build Securacy and evaluated its use by another set of 218 anonymous participants who installed the application from the Google Play store. Our results show that access to address book information is by far the biggest privacy concern. Over half (56.4%) of the connections made by apps are insecure, and the destination of the majority of network traffic is North America, regardless of the location of the user. Our app provides unprecedented insight into Android applications' communications behavior globally, indicating that the majority of apps currently use insecure network connections.

The papers in this special section provide the opportunity for researchers, practitioners, and application developers to review and discuss the state-of-the-art and trends of MCS (mobile crowd sensing)techniques and applications or propose new solutions. The ubiquitous sensor-rich mobile devices (e.g., smartphones, wearable devices, and smart vehicles) have been playing an increasing important role in the evolution of the Internet of Things (IoTs), which bridges the digital space and physical space at a societal scale. Their powerful computing/communication capacities, huge population, and inherent mobility make mobile-device networks a much more flexible and cost-effective IoT solution than static sensor networks.

On-demand mobile workforce applications match physical world tasks and willing workers. These systems offer to help conserve resources, streamline courses of action, and increase market efficiency for micro- and mid-level tasks, from verifying the existence of a pothole to walking a neighbor's dog. This study reports on the motivations and experiences of individuals who regularly complete physical world tasks posted in on-demand mobile workforce marketplaces. Data collection included semi-structured interviews with members (workers) of two different services. The analysis revealed the main drivers for participating in an on-demand mobile workforce, including desires for monetary compensation and control over schedules and task selection. We also reveal main reasons for task selection, which involve situational factors, convenient physical locations, and task requester profile information. Finally, we discuss the key characteristics of the most worthwhile tasks and offer implications for novel crowdsourcing systems for physical world tasks.

Today, people have the opportunity to opt-in to usage-based automotive insurances for reduced premiums by allowing companies to monitor their driving behavior. Several companies claim to measure only speed data to preserve privacy. With our elastic pathing algorithm, we show that drivers can be tracked by merely collecting their speed data and knowing their home location, which insurance companies do, with an accuracy that constitutes privacy intrusion. To demonstrate the algorithm's real-world applicability, we evaluated its performance with datasets from central New Jersey and Seattle, Washington, representing suburban and urban areas. Our algorithm predicted destinations with error within 250 meters for 14% traces and within 500 meters for 24% traces in the New Jersey dataset (254 traces). For the Seattle dataset (691 traces), we similarly predicted destinations with error within 250 and 500 meters for 13% and 26% of the traces respectively. Our work shows that these insurance schemes enable a substantial breach of privacy.

This paper studies the security and memorability of free-form multitouch gestures for mobile authentication. Towards this end, we collected a dataset with a generate-test-retest paradigm where participants (N=63) generated free-form gestures, repeated them, and were later retested for memory. Half of the participants decided to generate one-finger gestures, and the other half generated multi-finger gestures. Although there has been recent work on template-based gestures, there are yet no metrics to analyze security of either template or free-form gestures. For example, entropy-based metrics used for text-based passwords are not suitable for capturing the security and memorability of free-form gestures. Hence, we modify a recently proposed metric for analyzing information capacity of continuous full-body movements for this purpose. Our metric computed estimated mutual information in repeated sets of gestures. Surprisingly, one-finger gestures had higher average mutual information. Gestures with many hard angles and turns had the highest mutual information. The best-remembered gestures included signatures and simple angular shapes. We also implemented a multitouch recognizer to evaluate the practicality of free-form gestures in a real authentication system and how they perform against shoulder surfing attacks. We discuss strategies for generating secure and memorable free-form gestures. We conclude that free-form gestures present a robust method for mobile authentication.

This is a video demonstration for a full paper available in MobiSys'14 proceedings http://dx.doi.org/10.1145/2594368.2594375. The video demonstrates several forms of authentication on a common tablet, and compares them to our method for gesture-based authentication. Our method measures the security and memorability of user generated free-form gestures by estimating the mutual information of repeated gestures. We show examples of such gestures with high and low mutual information content. We also show what information from each is visible to a shoulder surfing attacker, and describe how our system is resistant to such an attack.

As we are surrounded by an ever-larger variety of post-PC devices, the traditional methods for identifying and authenticating users have become cumbersome and time consuming. In this paper, we present a capacitive communication method through which a device can recognize who is interacting with it. This method exploits the capacitive touchscreens, which are now used in laptops, phones, and tablets, as a signal receiver. The signal that identifies the user can be generated by a small transmitter embedded into a ring, watch, or other artifact carried on the human body. We explore two example system designs with a low-power continuous transmitter that communicates through the skin and a signet ring that needs to be touched to the screen. Experiments with our prototype transmitter and tablet receiver show that capacitive communication through a touchscreen is possible, even without hardware or firmware modifications on a receiver. This latter approach imposes severe limits on the data rate, but the rate is sufficient for differentiating users in multiplayer tablet games or parental control applications. Controlled experiments with a signal generator also indicate that future designs may be able to achieve data rates that are useful for providing less obtrusive authentication with similar assurance as PIN codes or swipe patterns commonly used on smartphones today.

Smartphone security research has produced many useful tools to analyze the privacy-related behaviors of mobile apps. However, these automated tools cannot assess people's perceptions of whether a given action is legitimate, or how that action makes them feel with respect to privacy. For example, automated tools might detect that a blackjack game and a map app both use one's location information, but people would likely view the map's use of that data as more legitimate than the game. Our work introduces a new model for privacy, namely privacy as expectations. We report on the results of using crowdsourcing to capture users' expectations of what sensitive resources mobile apps use. We also report on a new privacy summary interface that prioritizes and highlights places where mobile apps break people's expectations. We conclude with a discussion of implications for employing crowdsourcing as a privacy evaluation technique.

As we are surrounded by an ever-larger variety of post-PC devices, the traditional methods for identifying and authenticating users have become cumbersome and time-consuming. In this paper, we present a capacitive communication method through which a device can recognize who is interacting with it. This method exploits the capacitive touchscreens, which are now used in laptops, phones, and tablets, as a signal receiver. The signal that identifies the user can be generated by a small transmitter embedded into a ring, watch, or other artifact carried on the human body. We explore two example system designs with a low-power continuous transmitter that communicates through the skin and a signet ring that needs to be touched to the screen. Experiments with our prototype transmitter and tablet receiver show that capacitive communication through a touchscreen is possible, even without hardware or firmware modifications on a receiver. This latter approach imposes severe limits on the data rate, but the rate is sufficient for differentiating users in multiplayer tablet games or parental control applications. Controlled experiments with a signal generator also indicate that future designs may be able to achieve datarates that are useful for providing less obtrusive authentication with similar assurance as PIN codes or swipe patterns commonly used on smartphones today.

Today's identification and authentication mechanisms for touchscreen-enabled devices are cumbersome and do not support brief usage and device sharing. To address this challenge, this work explores a novel form of "wireless" communication that exploits the capacitive touchscreens which are now used in laptops, phones, and tablets, as a signal receiver. Using a custom built hardware token, in the form of a wearable ring, we show a proof-of-concept system that transmits a user identification code to the mobile device through the touchscreen. This mechanism works without any modification to the hardware or the firmware of the mobile device.

There have been many location sharing systems developed over the past two decades, and only recently have they started to be adopted by consumers. In this paper, we present the results of three studies focusing on the foursquare check-in system. We conducted interviews and two surveys to understand, both qualitatively and quantitatively, how and why people use location sharing applications, as well as how they manage their privacy. We also document surprising uses of foursquare, and discuss implications for design of mobile social services.

We present the design, implementation, and evaluation of Caché, a system that offers location privacy for certain classes of location-based applications. The core idea in Caché is to periodically pre-fetch potentially useful location-enhanced content well in advance. Applications then retrieve content from a local cache on the mobile device when it is needed. This approach allows an end-user to make use of location-enhanced content while only revealing to third-party content providers a large geographic region rather than a precise location. In this paper, we present an analysis that examines tradeoffs in terms of storage, bandwidth, and freshness of data. We then discuss the design and implementation of an Android service embodying these ideas. Finally, we provide two evaluations of Caché. One measures the performance of our approach with respect to privacy and mobile content availability using real-world mobility traces. The other focuses on our experiences using Caché to enhance user privacy in three open source Android applications.

Open-access 802.11 wireless networks are commonly deployed in cafes, bookstores, and other public spaces to provide free Internet connectivity. These networks are convenient to deploy, requiring no out-of-band key exchange or prior trust relationships. However, such networks are vulnerable to a variety of threats including the evil twin attack where an adversary clones a client's previously-used access point for a variety of malicious purposes including malware injection or identity theft. We propose defenses that aim to maintain the simplicity, convenience, and usability of open-access networks while offering increased protection from evil twin attacks. First, we present an evil twin detection strategy called context-leashing that constrains access point trust by location. Second, we propose that wireless networks be identified by uncertified public keys and design an SSH-style authentication and session key establishment protocol that fits into the 802.1X standard. Lastly, to mitigate the pitfalls of SSH-style authentication, we present a crowd-sourcing-based reporting protocol that provides historical information for access point public keys while preserving the location privacy of users who contribute reports.

Host mobility presents a challenge for security protocols. For example, many proposals exist for integrating IPsec to mobile IP. However, the existing approaches are cumbersome to configure and contain many round trips for security and mobility updates. The host identity protocol (HIP) is being developed in the IETF to provide secure host mobility and multihoming. The default way to operate the protocol is that the connection initiator knows the peer's public key or a hash of the public key. This requires either infrastructure support or pre-configuration which introduces difficulties for deploying the protocol. In this paper, we present an implementation and evaluation of HIP that creates leap-of-faith security associations. The implemented approach establishes end-to-end security without requiring any new infrastructure to be deployed. We argue that since worldwide PKI is nowhere near, and seems to nearly impossible to deploy in practice, leap-of-faith security is enough for Internet access and mobility. In our view, the deployment of opportunistic HIP even makes the deployment of DNSSEC unnecessary for most applications.

It is usual for 802.11 WLAN clients to probe actively for access points in order to hasten AP discovery and to find "hidden" APs. These probes reveal the client's list of preferred networks, thus, present a privacy risk: an eavesdropper can infer attributes of the client based on its associations with networks. We propose an access-point discovery protocol that supports fast discovery and hidden networks while also preserving privacy. Our solution is incrementally deployable, efficient, requires only small modifications to current client and AP implementations, interoperates with current networks, and does not change the user experience. We note that our solution is faster than the standard hidden-network discovery protocol based on measurements on a prototype implementation. Copyright 2009 ACM.

Unsolicited bulk email or spam is a menace to the usability of Internet email. The possibility of cheap Voice over IP (VoIP) services have introduced the threat of Spam over Internet Telephony (SPIT). A previously unexperimented solution for tackling the spam machinery is to increase its cost via Human Interactive Proofs (HIP). These proofs are basically applicable to all kind of spam, including email, but we concentrate on the Session Initiation Protocol (SIP) in this paper. Our approach allows the use of varying kinds of HIPs to prevent automated call connection attempts. The HIPs are used as an enrollment feature for configuring the call-recipient's call pass or block lists. By giving a proof of humanity, the caller is automatically put e.g. to the call-recipient's graylist for further processing by the user. The approach can be also used to mitigate unsolicited call connection attempts made by humans. We also present our SIP signaling based solution to address the SPIT threat.

We present an Online Teaching Environment (OTE) that supports "learning by doing" philosophy in teaching telecommunications software and routing. "Learning by doing" is achieved by giving students a programming assignment that introduces them to socket programming and gives them the opportunity to practice implementing simplified routing protocols. The OTE creates individual assignments for students, accepts solution submissions via the Internet, and, finally, checks the assignments automatically. The system also notifies the students of possible mistakes in their solutions, so they can learn from their mistakes, fix them and resubmit the corrected solutions. The teacher needs only to start the system when the course begins and verify the assignment results when students have finished their work.

At Helsinki University of Technology, in Telecommunications Software and Multimedia Laboratory we give a course titled "Computer Networks". One of the learning objectives of the course is network programming and routing. Our philosophy of teaching is "learning by doing", which means in practice that one of the requirements for passing the course is a programming assignment. The programming assignment introduces the student to socket programming and gives the student the possibility to practice implementing simplified routing protocols.The solutions to the programming assignments have previously been demonstrated to assistants and the reports were submitted as paper printouts and all students have done the same assignment. The students have complained that the submission method is out-of-date and inappropriate for a course about computer networks since the course curriculum includes many examples of applications that could be used to submit the assignments over the Internet.To answer the above requirements and to reduce the work load of the course personnel without hindering the students learning process, we are implementing an online learning environment for the Computer Networks course. This system creates and sends individual assignments for students, accepts solution submissions via the Internet, and, finally, checks them automatically. The system also notifies the students of possible mistakes in their solutions. This way, the students can learn from their mistakes and fix them and resubmit the corrected solutions. The goal of the implementation is that the teacher only needs to start the system when the course begins and verify the assignment results when students have finished their work.We can achieve multiple learning objectives simultaneously with this online learning system. The students learn how to implement simple user authentication, how to implement real working network programs for the Internet with different application programming interfaces (APIs), and learn how to apply the routing theory into practice. The submission using the Internet frees students from the boundaries of time and place since course assignments can be solved when and where students want to do them. Automatic correction gives fast feedback and allows students to learn from their own mistakes because they can still remember what they have done.The course provides a server and students implement corresponding client software to contact the server. In this phase of the assignment, students rehearse their knowledge of concurrent network programming. The server emulates a network that has several routers. A student's client represents one router whose routing table is calculated on the basis of the information sent by the server. The server can send routing data that is based on simplified versions of routing protocols such as distance vector or link state protocols. In other words, the second phase of the assignment is for learning routing in an internetwork.We believe that our system will have strong positive impact on learning results. Routing is one of the most difficult concepts related to computer networks. Theoretical studying alone does not help to understand the real practical problems. In addition, our system allows combining theory and practicalities since theory presented in the course lectures can be immediately applied in students' own work in a very concrete way.

Multicast address allocation in the Internet has been the focus of much research and standardization. However, the multicast address allocation problem has been overlooked in ad hoc networking research. In this paper, we survey approaches to solving the multicast address allocation problem and analyze the security characteristics of the proposals. We show that using random assignment in IPv6 based ad hoc networks for multicast address allocation is more secure and bandwidth efficient than the previous proposals. We use passive listening to obtain network prefixes for autoconfiguring a global multicast address. The ideas presented in this paper are useful for practical deployment of ad hoc networks

Pairing of wireless mobile devices requires an initial secure channel. A common approach is to use human as the secure channel or use an alternative medium such as a USB cable. However, we would like to minimize the involvement of users in the process. We propose a secure channel mechanism based on restricting the physical layer coverage for the initialization phase. Our system allows secure pairing between heterogeneous devices. After the pairing, the devices can be used even in multihop networks and through multiple interfaces, if available. The approach is general and thus can be applied to varying key exchange protocols and physical layer technologies.