CovertCast

We design, implement, and evaluate CovertCast, a censorship circumvention system that broadcasts the content of popular websites in real-time, encrypted video streams on common live-streaming services such as YouTube. CovertCast does not require any modifications to the streaming service and employs the same protocols, servers, and streaming software as any other user of the service. Therefore, CovertCast cannot be distinguished from other live streams by IP address filtering or protocol fingerprinting, raising the bar for censors.

This is proof of concept code and should NOT be used in production without further refining and testing of security.

See CovertCast-PETS16.pdf for details.

Dependencies

Both the client and server use Python3. The client is designed for Windows and also makes use of C++. The server is designed for Linux. If one operating system is desired, it will probably easier to port the client to Linux than the server to Windows.

Client (Windows)

pywin32 Download and install

nghttp2 My own personal hack

Server (Linux)

ffmpeg So annoying to get right <- Install instructions may be out of date.

ghost.py sudo pip install Ghost.py

Both

numpy sudo apt-get install python3-numpy (Windows)

cv2 sudo apt-get install python3-opencv (Windows)

PIL sudo pip install Pillow

reedsolo sudo pip install reedsolo

bitstring sudo pip install bitstring

How to use

The client code is written for Windows. The server runs on Linux.

1. Start up a RTMP live stream on YouTube.
2. Run broadcast-yt.sh on the server (edit the script for your RTMP). If there is no out.jpg, run python3 server for a second and then stop it.
3. Load the stream on the client in a browser (bigger box. not full screen. 720p video).
4. Load another browser using an HTTP2 proxy pointed at the h2ip in h2clientweb.py.
5. Start python3 client.py on the client.
6. Start the screen scraping code on the client.
7. Start python3 server.py on the server.

Parts

Information about the individual code in each folder.

covertcast

Contains the source code needed to run the thing.

broadcast-yt.sh Creates a silent RTMP video from out.jpg and streams it to YouTube. You'll need to update the YouTube RTMP URL.

client.py Launches the client version of the code. See options with python3 client.py --help

server.py Launches the server version of the code. See options with python3 server.py --help

config

Some stored configuration files. config-server is read in server.py.

logger

Code used for logging and debugging.

obj

Python lib containing some named tuples used in HTTP management.

prefetching

The library we use for picking what links to prefetch.

util

Some various utility functions.

video

Code used in the modulation and demodulation of data and video.

clientframes2data.py converts individual images to data

clientvideo2frames.py converts video to individual frames

functions.py modulates/demodulates data (or metadata) from a frame

modulate.py deals with metadata and calls functions.py for frames/data

parameters.py hardcoded parameters

servervideo.py used to help create images and save them for ffmpeg

tests.py tests stuff

valid_image.py tests if a CovertCast image is valid

video_helper_functions.py lots of little things

web

Handles the HTTP/proxy stuff

We call the code that directs the web scraper ``guides''. Currently they load the main page of a news site and then iterate through the linked stories, sending one of them at a time.

The folder README covers a lot of important stuff

fake* are versions used for testing

h2* are newer versions of the web code. You should use these

h2guides picks what stories to read

screenscraper

C code used to scrap a browser window in Windows. Change the hwnd variable in main to use a different browser/streaming service. Interacts with code in covertcast/video/clientvideo2frames.py