TorKameleon

TorKameleon is a solution designed to protect Tor users with increased censorship resistance against powerful traffic correlation attacks carried out by global adversaries. The system is based on flexible K-anonymization input circuits that can support TLS tunneling and WebRTC-based covert channels before forwarding users' original input traffic to the Tor network. Our goal is to protect users from correlation attacks through machine learning between incoming user traffic and the observed traffic at different Tor network intermediate relays or outgoing traffic to destinations. TorKameleon is the first system to implement a Tor pluggable transport based on both parameterizable TLS tunneling or WebRTC-based covert channels. We have implemented the TorKameleon prototype and performed extensive validations to observe the correctness and experimental performance of the proposed solution in the Tor environment.

The design, implementation and evaluation of the system is also described in our Arxiv 2023 paper. (To be published in TrustCom 2023)

@misc{vilalonga2023torkameleon,
      title={TorKameleon: Improving Tor's Censorship Resistance with K-anonymization and Media-based Covert Channels}, 
      author={Afonso Vilalonga and João S. Resende and Henrique Domingos},
      year={2023},
      eprint={2303.17544},
      archivePrefix={arXiv},
      primaryClass={cs.CR}
}

This code was implemented in the context of the dissertation:

@mastersthesis{TorKameleon, 
 author       = {Afonso Vilalonga},
 title        = {TorKameleon-Improving Tor's censorship resistance with K-anonymization media morphing covert input channels},
 school       = {NOVA School of Science and Technology}, 
 year         = 2022, 
 month        = 9,
}

Repo Folders

The repository currently consists of four different folders:

• The Client folder, which contains the code and configuration files for the client simulator Java program;
• The Deployment folder, which contains the Docker and configuration files for deploying TorKameleon in different modes and for deploying all the necessary components to create the setup described below;
• The HttpServer folder, which contains the code and configuration files for the HTTP Java server;
• The PT folder, which contains the code and configuration files for the TorKameleon software (including the necessary WebRTC-based application code and configuration files).

Prerequisites

Depending on how the TorKameleon is used, different prerequisites are required. If the deployment files are used (strongly recommended):

• Docker (any version should do it, but the version used was 20.10.16);
• Docker compose (any version should do it, but the version used was 2.8.0);
• Ubuntu (20.04 and above)

When running TorKameleon with the jars (not recommended), the system has been tested with the following software versions:

• Java 11
• Maven 3.8.1
• NodeJS
• Stunnel 5.62 (higher versions should work)
• Tor 0.4.6.7 (higher versions should work)
• Ubuntu 20.04

Setup

In our experiments, we used a setup similar to the one shown in the figure above. There are five main components in this setup:

• The local machine, which is used as the client and runs the TorKameleon Proxy locally;
• The TorKameleon Proxy, which receives the encapsulated data from the local machine via a WebRTC-based covert channel or TLS tunnel;
• The TorKameleon Tor Bridge, which receives the encapsulated data from the TorKameleon Proxy over a WebRTC-based covert channel or TLS tunnel;
• The HTTP server, which is used as the final destination for the client (the HTTP server can also be deployed as a hidden service);
• The STUN / TURN server used as a STUN and or TURN server for the WebRTC connections.

The setup can also be used without the Tor network component (TorKameleon Tor Bridge, Tor Middle Relay, and Tor Exit Relay) by forwarding traffic between the local machine and the proxy and from the proxy to the HTTP server, or without the proxy component by having the local machine forward traffic directly to the TorKameleon Tor Bridge.

Configuration

There are two main configurable components in the TorKameleon system: the TorKameleon core and the WebRTC-based application. It is also possible to configure the deployment files, but these are only configurations of the test deployment, which in turn are configurations of the two aforementioned components.

WebRTC Config Files

The WebRTC-based configuration files can be accessed via the folders PT/WebRTC/Bridge/public/config/ or PT/WebRTC/Client/public/config/. There is also a Signaling server that can be configured at PT/WebRTC/Signalling/config/.

The PT/WebRTC/Bridge/public/config/ configures the WebRTC-based web application in receiver mode (the web application that receives and accepts all incoming WebRTC connections to a TorKameleon Tor Bridge or TorKameleon Proxy). There are three configurable fields in the configuration file:

• window.webrtc: used to specify the IP and credentials of the TURN and STUN server and whether to use a TURN server (by adding in iceTransportPolicy: 'relay',);
• window.signalling_server: used to specify the IP and port of the signaling server. It must always be localhost, but the port may change (although it must be the same port configured in the Signaling server configuration file);
• window.tor_conn_addr: used to specify the IP and port of the WebSocket connection to the TorKameleon core software (it works like an interprocess connection between the TorKameleon Java core and the web application). It must always be localhost, but the port can change (although it must be the same port configured in the TorKameleon core configuration file);

The PT/WebRTC/Client/public/config/ configures the WebRTC-based web application in initiator mode (the web application that starts the WebRTC connections received by a TorKameleon Tor Bridge or Proxy). The configuration file is the same as the first one, with three exceptions:

• window.signalling_server: instead of being just a localhost address, in the web application in initiator mode it is an array of addresses, where the first position is always the address of the TorKameleon Tor bridge (if no TorKameleon Tor bridge is used, the first position of the array must be the string "null") and after that, the addresses represent the TorKameleon proxies that make up the pre-staged network. The addresses of the proxies must be in the same order as in the TorKameleon core network configuration file;
• window.local_node_addr: is used to make a WebSocket connection to nodeJS's local server to get from it the position in the array of signaling server addresses to which it will try to connect. The address must always be localhost, but the port may change (although it must be the same as configured in the TorKameleon core configuration files);
• window.modulation: the encapsulation method ("add" or "replace") to be used in the WebRTC-based covert channel;

The Signaling server can also be configured, namely:

• port: The port assigned to the signaling server;
• pem: Location of the pem file for the secure WebSocket connections to the signaling server;
• key: Location of the key file for the secure WebSocket connections to the signaling server;

TorKameleon Core Config Files

There are two configurable files for the TorKameleon core: the network configuration file and the config.properties configuration file. They are both located in the PT/Config/ folder.

config.properties File

The config.properties is a file used to configure all possible configurations in the TorKameleon core system. It has the following properties:

• tor_buffer_size: the size of the Tor cells (should be left at the default value, it is the same size used by the Tor network);
• number_of_nodes: the number of TorKameleon proxies in the pre-staged network;
• bypass_timer: the time in seconds required to switch the next proxy to which the data is forwarded;
• remote_host, remote_port: the IP and port of the target destination (the IP and port of the HTTP server);
• local_port_unsecure, local_port_secure, and streaming_port_proxy: the open ports for incoming TCP and UDP, TLS and DTLS, and WebRTC protocol handshake connections respectively (should be left as default);
• tor_port, tor_ip, and control_tor_port: open port and IP of the Tor client for connections between the Tor client and TorKameleon and the open control port of the Tor client (configured in the torrc file, all these configurations should be left as default);
• stunnel_port: open port on the receiving TorKameleon Proxy (to where the connections will be made) for the stunnel SSL tunnel (should be left as default);
• connect_streaming: open port on the receiving TorKameleon Proxy (to where the connections will be made) for incoming connections of the WebRTC protocol handshake (should be left as default);
• modulation: type of modulation used for the TorKameleon Proxy and TorKameleon pluggable transport (streaming or stunnel);
• pt_client_port: open port for the SOCKS5 proxy for the TorKameleon pluggable transport (should be left as default);
• pt_server_port: open port for the reverse proxy for the TorKameleon pluggable transport (should be left as default);
• or_port: open ORport of the Tor client configured in the torrc file (should be left as default);
• keystore, password, and key: location of the keystore, password of the Keystore and location of the key file for the secure communication used for the protocols and SSL tunnels;
• client_streaming_port: open port for the local nodeJS server serving the web application in initiator mode (should be left as default);
• bridge_streaming_port: open port for the local nodeJS server serving the web application in receiver mode (should be left as default);
• webdriver_location: the location of the web driver for the Chrome driver used in the Selenium framework;
• proxy_buffer_size: the size of the encapsulated data between TorKameleon Proxies;
• pt_buffer_size: the size of the encapsulated data between the client-side TorKameleon pluggable transport and the server-side TorKameleon pluggable transport;
• websocket_port: open port for the WebSocket server used to communicate with the web application (should be left as default);
• webrtc_location: the location of the WebRTC files;
• watch_video: used to launch the Chrome browser with or without a graphical user interface;

network File

The addresses of the Proxies are configured in the network file. The Proxies should be added in the following format: IP-Encapsulation_method-Order_number, where IP is the IP of the Proxy, Encapsulation_method is the type of encapsulation to be used with this specific Proxy (s, i.e. streaming, or t, i.e. TLS), and Order_number is the number of the Proxy in the network file (the first in the file is 1, the second in the file is 2, etc.). The window.signalling_server property of the WebRTC web application in initiator mode follows the same order in the array as in the network file.

Configuration Examples

Examples of how to configure various components (proxies, bridges, clients, etc.) can be found in the Deployment folder or via the links below. Note: 0000 in the fields of the config.properties file means that the field is not used for this configuration. The volume field in each Docker compose file should be changed with the specific location of the code on the current machine.

• TorKameleon Tor Bridge configuration files;
• HTTP server (normal) configuration files;
• HTTP server (hidden service) configuration files;
• Client-side TorKameleon pluggable transport configuration files;
• Client-side TorKameleon pluggable transport and TorKameleon Proxy configuration files;
• Local Proxy (used to connect to other TorKameleon Proxies) configuration files;

Deployment

The deployment folder contains two folders, the /Deployment/Coturn/ folder and the /Deployment/Setup/ folder.

Coturn Folder

The Coturn folder contains the configuration file for configuring the Coturn TURN and STUN server. To deploy the Coturn server on a machine, the following command should be used, using the configuration file in the Coturn folder:

docker run -d --network=host -v $(pwd)/my.conf:/etc/coturn/turnserver.conf coturn/coturn

The coturn configuration file should be moved to the current directory.

Setup Folder

The setup folder has six different folders that have different operating modes of TorKameleon and provide different configurations of the system. To deploy each component, the following command must be run in the particular folder to be deployed:

docker compose up

• /Deployment/Setup/Bridge/: Contains the configuration files necessary to deploy TorKameleon as a server-side pluggable transport (TorKameleon Tor Bridge);
• Deployment/Setup/HttpServer/: Contains the configuration files necessary to deploy the HTTP server as a normal HTTP server for testing purposes;
• /Deployment/Setup/HttpServerHS/: Contains the configuration files required to deploy the HTTP server as a hidden service HTTP server for testing purposes;
• /Deployment/Setup/LocalPTClienForBridge/: Contains the configuration files necessary to deploy TorKameleon as a client-side pluggable transport. Has two Docker Compose files. One is used to set up the client-side pluggable transport and automatically launch a client that downloads files from an HTTP server. The other only launches the client-side pluggable transport and exposes port 1234 so that the client application can connect and send download requests, and port 9050 so that applications can connect to the Tor client SOCKS and use it as a proxy that routes traffic through the TorKameleon pluggable transport;
• Deployment/Setup/LocalTirClientForProxy/: Contains the configuration files necessary to deploy TorKameleon as a network Proxy and as a client-side pluggable transport. It is used to receive traffic from other Proxies and route it to the Tor network;
• /Deployment/Setup/Proxy/: Contains the configuration files necessary to set up TorKameleon as a network Proxy that forwards traffic to other proxies on the network;

Usage

TorKameleon is Docker-friendly and should be used in containers configured like those in the deployment folder. However, it can also be run on a machine without Docker by compiling the Maven project and running the jar file. Other deployments can be configured and we recommend users to check the deployment folder and test the different configurations for the system and operating modes.

Client

The client should only be run when the TorKameleon environment is set up. The client software is started by launching the client's maven project jar. The following command should be used:

java -jar name_of_jar mode arg1 arg2 ...

There are several modes of operation of the client software, and each mode may have different arguments. The following are the operating modes of the client software:

• interactive: the user must manually enter the input (path and protocol) required for the file download. Example: java -jar name_of_jar interactive and ../Files/large tcp;
• async: The program automatically sends requests to the HTTP server with a cool-down time of X seconds (configurable) between requests, but the user must pass the number of client threads the program should use. Example: java -jar name_of_jar async 2 (to start two clients in parallel sending download requests to the HTTP server);
• async/notimer: The program automatically sends X requests to the HTTP server, without a cool-down period between requests. The user must specify the number of client threads, the protocol, the file to download, and the number of requests each thread should make. Example: java -jar name_of_jar async/notimer tcp ../Files/large 2 2 (to run two clients in parallel, send the download requests for file large over the TCP protocol and perform two downloads for each thread);

There are four files available for download: ../Files/large, ../Files/small, ../Files/earth.jpg and ../Files/book.pdf. There are also four protocols available: tcp, dtls, udp and tcp.

HTTP Server

It can be deployed as a hidden service or as a normal HTTP server. Both are deployed by running docker compose up and for the normal HTTP server it is automatically ready to receive requests. For the hidden service, it is ready as soon as the 100% line appears on the console.

The HTTP server has three open ports that can be configured in /Client/Config/config.properties. These are:

• echo port: used to receive packets without sending responses;
• test port: used to receive httping requests and send an HTTP header response;
• normal_port: used for download requests;

TorKameleon Tor Bridge

The TorKameleon Tor Bridge is deployed by running the docker compose up command and is ready to receive connections once the Tor software is ready (once the 100% line appears on the console).

TorKameleon Proxy

The TorKameleon Proxy is deployed by running the docker compose up command and is ready when the Tor software is ready (as soon as the 100% line appears on the screen).