Abstract

Tor is a real-world, circuit-based low-latency anonymous communication
network, supporting TCP applications over the Internet. In this talk,
we will present a new class of attacks, protocol-level attacks,
against Tor. Different from existing attacks, these attacks can
confirm anonymous communication relationships quickly and accurately
by manipulating one single cell and pose a serious threat against
Tor. In protocol-level attacks, a malicious entry onion router may
duplicate, modify, insert, or delete cells of a TCP stream from a
sender. The manipulated cells traverse middle onion routers and arrive
at an exit onion router along a circuit. Because Tor uses the counter
mode AES (AES-CTR) for encrypting cells, the manipulated cells disrupt
the normal counter at exit onion routers and decryption at the exit
onion router incurs cell recognition errors, which are unique to the
investigated protocol-level attacks. If an accomplice of the attacker
at the entry onion router also controls the exit onion router and
recognizes such cell recognition errors, the communication
relationship between the sender and receiver will be
confirmed. Protocol-level attacks can also be used for launching the
denial-of-service (DoS) attack to disrupt the operation of Tor. We
systematically analyze the impact of these attacks. We have
implemented these attacks on Tor and our experiments validate their
effectiveness and efficiency. We also present guidelines for defending
against such attacks.


Speaker Bio


Dr. Xinwen Fu is an assistant professor in the Department of Computer
Science, University of Massachusetts Lowell. He received his
B.S. (1995) and M.S. (1998) in Electrical Engineering from Xi'an
Jiaotong University, China and University of Science and Technology of
China respectively. He obtained his Ph.D. (2005) in Computer
Engineering from Texas A&M University. Dr. Fu’s current research
interests are in network security and privacy, information assurance,
computer forensics, system reliability and networking QoS. He has been
publishing papers in conferences such as IEEE Symposium on Security
and Privacy (S&P), IEEE International Conference on Computer
Communications (INFOCOM) and IEEE International Conference on
Distributed Computing Systems (ICDCS), journals such as IEEE
Transactions on Parallel and Distributed Systems (TPDS), and book
chapters. His research is supported by NSF.