CrowdShare is a service that allows mobile users to securely share their internet access in a mobile crowd. It uses a mesh network for routing between participants and addresses security, anonymity, liability, and access control concerns. The implementation for Android extends an existing mesh networking platform and adds encryption, signed requests, and a "Friend of Friend" service to control sharing. Several technical challenges were addressed including enabling WiFi and 3G simultaneously and dynamic access control on Android devices. CrowdShare aims to enable arbitrary sharing of resources between anonymous users while ensuring confidentiality, authenticity, and accountability.

1. CrowdShare
Secure Resource Sharing in Mobile Crowds
Stanislaus Stelle
CASED / TU Darmstadt
8th of March 2013 on Moosecon
Joined work with
Alexandra Dmitrienko | Ahmad-Reza Sadeghi | Elena Reshetova | Thomas Schneider | N. Asokan
1

2. Motivation
2

3. Motivation
Resource Sharing
3

4. Motivation
Resource Sharing
Collaborative work
4

5. Motivation
Resource Sharing
Collaborative work
Social Networks
5

6. Motivation
Resource Sharing
Collaborative work
Social Networks
Mobile
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7. Depends on
Carrier
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8. 4.6 billions without
Internet
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9. 4.6 billions without
Internet
Focus on Internet
Availability
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10. What can we
do about it
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11. Existing Technology: Tethering
Participant
Participant
Access Point
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12. Existing Technology: Tethering
Range
Participant
Participant
Access Point
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13. Existing Technology: Tethering
Range
Password
Distribution
Password Participant
Participant
Access Point
Password
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14. Solution: Multihop Resource
Sharing 14

15. How should
this work?
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16. Mesh Network Routing: BATMAN
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17. What about
security?
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18. Link Security

19. Link Security Access Control

20. Anonymity
Link Security Access Control
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21. Liability
Anonymity
Link Security Access Control
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22. Implementation
for Android
Link Security – SSL/VPN
Anonymity – Registration with Certs.
Liability – Signed Resource Requests
Access Control – FoF Service

23. And what
about
liability?
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24. Liability
Internet
Wants to tether Has Internet Connection
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25. Liability
25

26. Liability
26

27. Liability
27

28. Bound to phone number Liability
Destination IP, Protocol, Port, Timestamp
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29. Liability
29

30. Liability
30

31. Liability
31

32. Liability
32

33. Liability
33

34. Liability
34

35. And what
about
access
control?
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36. Friend of Friend Service
Simple alternative
Fancy alternative
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37. Simple alternative
register
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38. Simple alternative
sync
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39. Simple alternative
Transmit
Whitelists
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40. Fancy alternative
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41. Challenges
WiFi and 3G at the same time
WiFi in Ad-Hoc mode
Dynamic Access Control

42. WiFi and 3G at the same time
Android prohibits both to be activated
insmod /system/lib/modules/bcm4329
firmware_path=/system/vendor/firmware/fw_bcm4329.bin

43. WiFi in Ad-Hoc mode
No System option in Android
iwconfig eth0 channel 11 essid Mesh mode ad-hoc
ifconfig eth0 10.0.0.1 netmask 255.0.0.0 up

44. Dynamic Access Control
Friend of Friend Service
Liability Feature

45. Conclusion
1) Design of CrowdShare service for secure resource sharing
a. Allows arbitrary people to establish mesh and share resources
b. Enables users to decide what and with whom to share
c. Ensures anonymity, liability, confidentiality, authenticity
2) Implementation for Internet sharing on Android devices
a. Extends Serval
b. Enables internet sharing
c. Brings in a security layer
d. Addresses a number of technical challenges

46. T ha n
k y ou
Ques
ti ons?

47. Stanislaus Stelle
Freelancer
stas.stelle@gmail.com