give us a real abstract

\begin{abstract}

We present Tor, a circuit-based low-latency anonymous communication

system. Tor is the successor to Onion Routing

and addresses various limitations in the original Onion Routing design.

Tor works on the real-world Internet, requires no special

privileges such as root- or kernel-level access,

requires little synchronization or coordination between nodes, and

provides a reasonable trade-off between anonymity, usability, and efficiency.

We include a new, more practical design for rendezvous points, and

close with a list of open problems in anonymous communication systems

today.

% Which other innovations from section 1 should we mention in the abstract?

system. This second-generation Onion Routing system addresses limitations

in the original design. We add perfect forward secrecy, congestion

control, directory servers, integrity checking, variable exit policies,

and a practical design for rendezvous points. Tor works on the real-world

Internet, requires no special privileges or kernel modifications, requires

little synchronization or coordination between nodes, and provides a

reasonable trade-off between anonymity, usability, and efficiency. We

close with a list of open problems in anonymous communication systems.

\end{abstract}

%\begin{center}

necessary, and the process of building circuits is more reliable, since

the initiator knows when a hop fails and can then try extending to a new node.

% Perhaps mention that not all of these are things that we invented. -NM

\item \textbf{Separation of protocol cleaning from anonymity:}

The original Onion Routing design required a separate ``application

proxy'' for each

\item \textbf{Leaky-pipe circuit topology:} Through in-band signalling

within the circuit, Tor initiators can direct traffic to nodes partway

down the circuit. This allows for long-range padding to frustrate traffic

shape and volume attacks at the initiator \cite{defensive-dropping}.

Because circuits are used by more than one application, it also allows

traffic to exit the circuit from the middle---thus frustrating traffic

shape and volume attacks based on observing the end of the circuit.

down the circuit. This novel approach allows both for long-range

padding to frustrate traffic shape and volume attacks at the initiator

\cite{defensive-dropping}, and, because circuits are used by more than one

application, allows traffic to exit the circuit from the middle---thus

frustrating traffic shape and volume attacks based on observing the end

of the circuit.

\item \textbf{No mixing, padding, or traffic shaping:} The original

Onion Routing design called for batching and reordering the cells arriving

to a hidden server, but these reply onions did not provide forward

security, and would become useless if any node in

the path went down or rotated its keys.

In Tor's current design, clients negotiate {\it

In Tor, clients negotiate {\it

rendezvous points} to connect with hidden servers; reply onions are no

longer required.

\end{tightlist}

We have implemented most of the above features. Our source code is

available under a free license, and is not (as far as we can tell)

encumbered by patents. We have

available under a free license, and we believe it to be

unencumbered by patents. We have

recently begun deploying a widespread alpha network to test

the design in practice, to get more experience with usability and users,

and to provide a research platform for experimenting with new ideas.

\Section{Related work}

\label{sec:related-work}

Modern anonymity systems date to Chaum's Mix-Net\cite{chaum-mix} design of

1981.  Chaum proposed hiding sender-recipient connections by wrapping

messages in layers of public key cryptography, and relaying them

Modern anonymity systems date to Chaum's Mix-Net\cite{chaum-mix}. Chaum

proposed hiding the correspondence between sender and recipient by

wrapping messages in layers of public key cryptography, and relaying them

through a path composed of ``Mixes.''  These mixes in turn decrypt, delay,

and re-order messages, before relaying them along the sender-selected

path towards their destinations.