Enabling Secure Secret Sharing in Distributed Online Social Networks

PDF
0.4MB

Le-Hung Vu
Ecole Polytechnique Fédérale de Lausanne (EPFL)
Switzerland

Sonja Buchegger
Deutsche Telekom Laboratories, TU Berlin (T-labs)
Germany

Anwitaman Datta
Nanyang Technical University
Singapore

Karl Aberer
Ecole Polytechnique Fédérale de Lausanne (EPFL)
Switzerland

Abstract:
We study a new application of threshold-based secret sharing schemes in a distributed online social network (OSN), where users need a means to back up and recover their private keys in a network of untrusted servers. Using a simple threshold-based secret sharing in such an environment is completely unsecured since delegates keeping the secret shares may collude to steal the user's private keys and possibly take control of their machines, infect them with malicious software and use them for further attacks. This leads to an epidemic that makes the whole system rapidly collapses.

To mitigate this problem, we propose using different techniques to improve the system security: by selecting only the most reliable delegates for keeping these shares and further encrypting the shares with passwords. We develop a mechanism to select most reliable delegates based on an effective trust measure: relationships among the secret owner, delegate candidates, and their related friends are used as a means to estimate the trustworthiness of each delegate. This trust measure minimizes the likelihood of the secret being stolen by an adversary and is shown to be effective against various collusive attacks. Our extensive simulation results show that the proposed trust-based delegate selection performs very well in highly vulnerable environments where the adversary controls many nodes with different distributions and even with spreading of infection in the network. In fact, the number of keys lost is very low under extremely pessimistic assumptions of the adversary model.