A New
Cell-Counting-Based Attack Against Tor
ABSTRACT:
Various
low-latency anonymous communication systems such as Tor and Anonymizer have
been designed to provide anonymity service for users. In order to hide the
communication of users, most of the anonymity systems pack the application data
into equal-sized cells (e.g., 512 B for Tor, a known real-world, circuit- based,
low-latency anonymous communication network). Via extensive experiments on Tor,
we found that the size of IP packets in the Tor network can be very dynamic
because a cell is an application concept and the IP layer may repack cells.
Based on this finding, we investigate a new cell-counting-based attack against Tor,
which allows the attacker to confirm anonymous communication relationship among
users very quickly. In this attack, by marginally varying the number of cells
in the target traffic at the malicious exit onion router, the attacker can
embed a secret signal into the variation of cell counter of the target traffic.
The embedded signal will be carried along with the target traffic and arrive at
the malicious entry onion router. Then, an accomplice of the attacker at
themalicious entry onion router will detect the embedded signal based on the
received cells and confirm the communication relationship among users. We have
implemented this attack against Tor, and our experimental data validate its
feasibility and effectiveness. There are several unique features of this
attack. First, this attack is highly efficient and can confirm very short
communication sessions with only tens of cells. Second, this attack is
effective, and its detection rate approaches 100% with a very low false
positive rate. Third, it is possible to implement the attack in a way that
appears to be very difficult for honest participants to detect (e.g., using our
hopping-based signal embedding).
ARCHITECTURE:
EXISTING
SYSTEM:
Most
existing approaches are based on traffic analysis. Passive traffic analysis technique will
record the traffic passively and identify the correlation between sender’s
outbound traffic and receiver’s inbound traffic based on statistical measures.
This type of technique requires a relatively long period of traffic observation
for a reasonable detection rate. The idea is to actively introduce special
signals into the sender’s outbound traffic with the intention of recognizing
the embedded signal at the receiver’s inbound traffic. Encryption does
not work, since packet headers still reveal a great deal about users.
DISADVANTAGE
OF EXISTING SYSTEM:
Ø Encryption
does not work, since packet headers still reveal a great deal about users.
PROPOSED
SYSTEM:
In this project, we focus on the active
watermarking technique, which has been active in the past few years. proposed a flow-marking scheme
based on the direct sequence spread spectrum technique by utilizing a
pseudo-noise code. By interfering with
the rate of a suspect sender’s traffic and marginally changing the traffic
rate, the attacker can embed a secret spread-spectrum signal into the target
traffic. The embedded signal is carried along with the target traffic from the
sender to the receiver, so the investigator can recognize the corresponding
communication relationship, tracing the messages despite the use of anonymous
networks. However, in order to accurately confirm the anonymous communication
relationship of users, the flow-marking scheme needs to embed a signal
modulated by a relatively long length of PN code, and also the signal is
embedded into the traffic flow rate variation. Houmansadr et al.
proposed a nonblind network flow watermarking scheme called RAINBOW for
stepping stone detection.
ADVANTAGE
OF PROPOSED SYSTEM:
Ø Active
watermarking technique can reduce attack lasting time.
Ø Improve
attack success rate and has recently received more attention.
MODULES:
1.
Data
Transmission,
2. Components of Tor,
3. Cells at Onion Routers
MODULES
DESCRIPTION:
Data Transmission:
In Tor, an maintains a connection to
other on demand. The uses a way of
source routing and chooses several from
the locally cached directory, downloaded from the directory caches. The number
of the selected is referred as the path length.We use the default path length
of three as an example. The iteratively establishes circuits across the Tor
network and negotiates a symmetric key with each, one hop at a time, as well as
handles the streams from client applications. The side of the circuit connects
to the requested destinations and relays the data. We now illustrate the
procedure that the establishes a circuit and downloads a file from the
server.
Components of Tor:
Onion routers are special proxies that
relay the application data. In Tor, transport-layer security connections are
used for the overlay link encryption between two onion routers. The application
data is packed into equal-sized cells. They hold onion router information such
as public keys for onion routers. Directory authorities hold authoritative
information on onion routers, and directory caches download directory
information of onion routers from authorities.
Cells at Onion Routers:
To begin with, the onion router receives
the data from the connection on the given port A. After the data is
processed by protocols, the data will be delivered into the buffer of the
connection. When there is pending data in the buffer, the read event of this
connection will be called to read and process the data. The connection read
event will pull the data from the buffer into the connection input buffer. Each
connection input buffer is implemented as a linked list with small chunks. The
data is fetched from the head of the list and added to the tail. After the data
in the TLS buffer is pulled into the connection input buffer, the connection
read event will process the cells from the connection input buffer one by one.
HARDWARE
REQUIREMENTS
•
SYSTEM : Pentium IV 2.4 GHz
•
HARD
DISK : 40 GB
•
FLOPPY
DRIVE : 1.44 MB
•
MONITOR : 15 VGA colour
•
MOUSE : Logitech.
•
RAM : 256 MB
•
KEYBOARD :
110 keys enhanced.
SOFTWARE
REQUIREMENTS
•
Operating system :- Windows XP
Professional
•
Front End :- Microsoft Visual Studio .Net 2008
•
Coding Language : - C# .NET.
REFERENCE:
Zhen Ling, Junzhou Luo, Member, IEEE, Wei Yu,
Xinwen Fu, Dong Xuan, and Weijia Jia, “A New Cell-Counting-Based Attack Against
Tor”, IEEE/ACM TRANSACTIONS ON
NETWORKING, 2012.
