Annual Report 2010 - Fachgruppe Informatik an der RWTH Aachen ...

World libraries : towards efficiently sharing large data volumes in open
untrusted environments while preserving privacy
Stefan Richter
Public libraries have served an invaluable function for a long time. Yet in an age of digital
media, traditional methods of publishing and distributing information become increasingly
marginalized. This thesis poses the question if and how information technology can be
employed to find functional alternatives, conforming to the needs of society that have been
changed by information technology itself. To this end we introduce the concept of world
libraries: Massively distributed systems that allow for the efficient sharing of large data
volumes in open, untrusted environments while preserving privacy. To begin with, we discuss
our definition as it relates to similar but different notions, then defend its utility with
philosophical, economical, and legal arguments. We go on to examine anonymous file sharing
systems with regard to their applicability for world libraries. We identify reasons why these
systems have failed to achieve popularity so far, as well as promising principles and structures
for successful world library implementations. Of these, distributed hash tables (DHTs) turn
out to be particularly important. That is why we study their security and privacy properties in
detail. Using both analytical models and simulation, weaknesses in earlier approaches are
shown, leading us to the discovery of the first practical DHT that scalably defends against
active adversaries. The fourth chapter is dedicated to general bounds on anonymity.
Anonymity techniques are important tools for the preservation of privacy. We present novel
attacks that endanger the anonymity provided by these tools under very general
circumstances, giving analytical lower bounds to the success probability of such attacks
measured in the number of adversarial observations. These results limit the applicability of
anonymity techniques in world library implementations and other privacy enhancing
technologies. Finally, we summarize our findings and their impact on world library design.
Evaluators: Prof. Dr. Peter Rossmanith (RWTH Aachen University)
Prof. Dr. Dr. h.c. Otto Spaniol (RWTH Aachen University)
Date of oral exam: 12 November 2009
489