Tor is anonymous commiunication network over the internet. In this paper that written by Xinwen Fu and Zhen Ling in Black Hat DC 2009 you can read 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. you can download this white paper from Here.... Enjoy.
