Date of Award


Degree Type



Electrical and Computer Engineering

First Advisor

Zhu, Ye

Subject Headings

Computer security, Computer networks -- Security measures, Routing (Computer network management)


An onion routing based anonymous communication system is developed to address timing analysis attacks, a common limitation of many contemporary anonymous systems including Tor. Timing analysis based attacks gained importance because simple payload check and packet inspection attacks are avoided by encrypting packets. Timing information gathered at one part of the network is correlated with information gathered at other parts to break the anonymity. Network coding, a recently developed packet forwarding technique, is used to disrupt timing attacks. The system uses a multicast tree of onion routers (OR) through which the packets are relayed to desired destinations. Packets from different users are grouped and linearly transformed over a finite field before forwarding them into the multicast tree. Encoding/transforming the packets evenly spreads the information among all encoded output packets making them equally important and informative. The system creates similar traffic pattern on all the links of the tree. Since the traffic pattern for all the ORs in the tree is similar, it becomes difficult to launch timing attacks. Extensive experiments are carried out for TCP communications using the Network Simulator-2 for different sizes of the multicast tree and probability of detecting a communication is equal to the probability detection through a random guess, equal to 1/n, where n is number of ORs in last layer of the multicast tree. By increasing the number of leaf ORs in the tree decreases the detection probability and increase the degree of anonymity