Optimizable Design Schemes in Communication Systems for Providing Anonymity and Confidentiality
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In applications requiring anonymity such as electronic mail, evading website censorship, and file sharing, the identities of source-destination pairs for each data flow should be untraceable. To achieve this goal, anonymous networks use covert relays to prevent unauthorized entities from determining communicating parties through traffic timing analysis. In a multipath anonymous network, the choice of which relay nodes should be covert, as well as the route selection by the network nodes, affect both the anonymity and network performance. Although assigning relays as covert and selecting routes composed of covert relays can provide higher anonymity, the selection of these two parameters will increase the packet dropping rate of the network. Therefore, how to choose relays as covert and how to select routes among multiple paths should be studied. In this thesis, we present analytical frameworks for relay assignment and route selection in multi-path anonymous wireless networks. We show that joint relay assignment and route selection can be formulated as a convex optimization problem which guarantees global optimum solution. Our frameworks also consider two special cases. The first case is the route selection alone by giving the relay configuration. The second case is choosing relays as covert or not given the route selection strategies. Given a subset of nodes is chosen to act as covert relays to hide timing information from unauthorized observers. We propose route selection methods that maximize anonymity for multipath wireless networks with predetermined covert relay nodes, while taking into account packet loss as a constraint. Using a rate-distortion framework, we show how to assign probabilities which split the flows from source to destination among all possible routes and show that selecting routes according to the assigned probabilities achieves maximum anonymity given the packet-loss constraint. When sources and destinations are independent to each other, each source allocates route independently as well. When sources destination pairs are dependent, we investigate how to allocate routes for each source-destination pair to maximize anonymity with packet-loss rate as a constraint. Since each source may have incomplete knowledge of which destination and routes other sources choose due to packet encryption and radio range, we consider three different cases depending on each source knowledge of other sources. In each case, we show how to split flows among multiple paths to maximize anonymity under packet-loss constraint by considering the optimization as a rate-distortion problem. The optimal relay configuration for given fixed route section can be derived from the information theoretic anonymity metric of joint relay and route selection. We showed that the problem of optimal relay assignment based on the trade-off between anonymity and throughput in a multiple wireless network can be solved by re-deriving rate-distorting frameworks. Our framework guarantees efficient computation of the global optimum. For RFID system, to ensure security and privacy of passive RFID have notoriously been a difficult problem. In a passive RFID system, each tag has power and computational constraints. As a result, providing privacy protection can be a very challenging task. In this thesis, we propose a physical layer privacy protection scheme termed Varying Reader’s Transmitted Amplitude (VRTA). This scheme provides the data confidentiality in the uplink direction. i.e., tag to reader. By doing so, the user’s privacy is assured against the passive eavesdroppers. This scheme requires no modifications on the tag and the existing protocols as well as no pre-shared secrets. It has minimal impact on the existing system. We also perform analysis to show our scheme is theoretically secure against one and multiple passive eavesdroppers with properly chosen system parameters. Then, by applying VRTA system, the RFID tag can establish key agreement with reader for encryption or authentication purpose. Finally, we implement our scheme using USRP to validate our theoretical results and to further test the performance of our proposed scheme.
- Electrical engineering