Overview ========

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 . The research paper is available at . Finally, the directory "doc/" in this repository contains ScrambleSuit's protocol specification.

Installation and Testing ========================

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:

• Clone and compile the current Tor-git (or use a version of your choice as

• Clone the current version of pyptlib (or use a version of your choice as

• Clone a modified version of obfsproxy which contains the scramblesuit

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.

Alternatives ============

Check out obfs4 which is an enhancement of ScrambleSuit.

Feedback ========

Contact: Philipp Winter OpenPGP fingerprint: B369 E7A2 18FE CEAD EB96 8C73 CF70 89E3 D7FD C0D0