This paper corresponds to publication: I. Krontiris, F.C. Freiling, "Urban Sensing through Social Networks: The Tension between Participation and Privacy", International Tyrrhenian Workshop on Digital Communications (ITWDC), Island of Ponza, Italy, September 2010. https://pi1.informatik.uni-mannheim.de/filepool/publications/ITWDC_2010.pdf

1. Participatory Sensing through Social NetworksThe tension between Participation and Privacy ITWDC6-8 September, 2010 I. Krontiris, Chair of Mobile Business Goethe University Frankfurt ioannis.krontiris@m-chair.net F.C. Freiling, LehrstuhlPraktischeInformatik I University of Mannheim

2. Paper outline What are the benefits and drawbacks of connecting social network with participatory sensing? We study this relation in 2 dimensions that conflict with each other: Social translucence (visibility) and Privacy Goal: Identify and discuss research challenges that arise in this new setting.

3. Available Sensors Today

4. Available Sensors Tomorrow

5. External Sensors

6. NoiseTube

7. Architecture Overview

8. Research Questions Share – How will collected data be shared? What practices of individual ownership will be appropriate and how will privacy be addressed? How can data best be shared with non-experts, urban planers, decision and policy makers, etc.? Change – What tools or frameworks best invite and encourage active participation? What tools and techniques will facilitate the most productive debate and ultimate positive social benefit?

9. Utilizing Social Networks Benefit 1: Recruitment (getting people to join) identify and reach well-suited participants for data collections based on their geographic availability as well as their interests and habits. allow existing participants to invite their friends to join a group, or see what their friends are doing (which group they joined, in which groups they are most active), etc.

10. Utilizing Social Networks Benefit 2: Participation (getting people to participate) No direct benefits for participants. Why should those who can produce the sensing data take the time to engage in such interactions? Why should they wish to? Sense of Community Sense of efficacy: a sense that they have had some effect on the group.

11. Utilizing Social Networks RecognitionReputation Points a user, after submitting a report from his mobile phone, is given a reputation point. reputation points are public and appear on the public profile of that user.

12. Utilizing Social Networks Benefit 3: Acting on the data Not all data are equally useful / important People could also intentionally submit fault data Pre-evaluation by the users Example: A system that allows users to submit images of potholes on the street

13. location privacy

14. Privacy vs. Visibility Knowing when a particular person was at a particular point in time can be used to infer a lot of personal information Allow users to make their contributions visible to the online community Anonymity Social Translucence

15. Research question System model: Users submitting data are anonymous, but at the same time they maintain a public profile in the social network, where they provide details about themselves (e.g. reputation, etc.) Is it possible to offer anonymity to the user, who submits sensing data from the physical environment, while at the same time we maintain properties connected with his public profile, like Reputation and User revocation?

16. br /> Anonymity Let’s assume we provide anonymity to protect user’s privacy Data are anonymized Hide network identifiers

17. Reputation Giving reputation points to an anonymous user is not possible Need two independent processes: A pseudonymous user acquires reputation points (one-time pseudonym) A known user updates its reputation in his public profile Solution direction: Use e-cash systems A pseudonymous user obtains e-coins from the bank for a report submission, which corresponds to a reputation point At a later point in time, the user logs-in using his public profile and redeems the e-coin to increase his reputation. Hard: Repetitions of this process should not be linkable!

18. User revocation Before submit, user authenticates anonymously to the service provider This encourages user misbehavior need for user revocation Revocation depends on anonymous authentication mechanism: If use group signatures: A Trusted-Third-Party manages user accounts and has the ability to revoke user’s anonymity at any time. No assurances that TTP is reliable! If use e-cash: Anonymity is revoked if spent an e-coin twice If use k-Times Anonymous Authentication: Anonymity is revoked if user authenticates more than k times. None of this appropriate. Need a d-strikes-out revocation system When users are judged to have misbehaved d times, they are revoked by the system Some protocols exist, but very expensive for power-limited mobile phones

19. Conclusions Utilization of social networks could provide many benefits in urban sensing recruit more citizens in campaigns and boost their active participation. Example: use of reputation systems It is also important to preserve the anonymity of the users submitting data Anonymity makes it hard to revoke misbehaving users or compute their accumulated reputation points Acknowledgment: Thanks to Nicolas Maisonneuve for the inspiring conversations