ScrambleSuit is a pluggable transport protocol for obfsproxy. It is written
in pure Python and solves two problems:
- Protection against active probing attacks by requiring a shared secret between the client and the server. This secret is communicated out-of-band via Tor's BridgeDB.
- Rudimentary defence against traffic analysis attacks by altering flow features. In particular, ScrambleSuit alters its inter-arrival times and packet length distribution.
Besides, ScrambleSuit's payload is computationally indistinguishable from randomness. Clients can authenticate themselves towards a ScrambleSuit bridge by conducting a modified UniformDH handshake or by redeeming a session ticket.
For a more detailed overview of ScrambleSuit, please have a look at the project page available at http://veri.nymity.ch/scramblesuit/. The research paper is available at http://veri.nymity.ch/pdf/wpes2013.pdf. Finally, the directory "doc/" in this repository contains ScrambleSuit's protocol specification.
The following instructions were tested on Debian wheezy but they should work just fine on other GNU/Linux distributions as well.
-
On a Debian wheezy system, the following packages are needed:
git,python-dev,python-gmpy,python-yaml,python-setuptools,automake,libevent-dev,libssl-dev,asciidoc -
Clone and compile the current Tor-git (or use a version of your choice as long as it is >= v0.2.5.0-alpha-dev):
git clone https://git.torproject.org/tor.git -
Clone the current version of pyptlib (or use a version of your choice as long as it is >= 0.0.5):
git clone https://git.torproject.org/pluggable-transports/pyptlib.git -
Clone a modified version of obfsproxy which contains the scramblesuit branch:
git clone -b scramblesuit_integration https://git.torproject.org/user/phw/obfsproxy.git
The directory "test/" in this repository contains two configuration files for
tor which provide a local (i.e., using the loopback interface) ScrambleSuit
setup. Furthermore, the script generate_secret.py can be used to generate
shared secrets for Tor's configuration file.
Check out obfs4 which is an enhancement of ScrambleSuit.
Contact: Philipp Winter phw@torproject.org
OpenPGP fingerprint: B369 E7A2 18FE CEAD EB96 8C73 CF70 89E3 D7FD C0D0