Architecture
Cloak’s architecture comprises three main components: the client, the bridge, and the broker, each serving a crucial role in enabling secure communication.
The client operates a Tor proxy that exposes a SOCKS interface to local applications, such as the Tor Browser or Tor’s command-line interface. It enables the tunneling of local Tor traffic by embedding it into video frames using the Protozoa encoders. These video frames are then sent through the video stream of a WebRTC-based carrier application, such as Jitsi Meet. At the bridge’s end these frames are decoded, after which the Tor traffic is routed to a Tor relay responsible for forwarding it to the “open” Tor network towards its destination.
The broker acts as a coordinator for all bridges forming Cloak’s infrastructure and runs a directory service that allows users to locate available bridges. Apart from users, two other main actors in the Cloak ecosystem are bridge providers and broker providers. Bridge providers contribute to the system by deploying server hardware and running Cloak’s bridge software. These providers can be volunteers, private organizations, or public non-profit institutions supporting internet freedom. On the other hand, the broker provider serves as a trusted authority responsible for coordinating bridge membership, ensuring compliance with community guidelines, proper deployment of Cloak, and adherence to safety and anonymity procedures.
To deploy a Cloak bridge, a bridge provider must:
Set up the server hardware
Install the Cloak software
Register the bridge in the broker service
Once deployed, the bridge listens for rendezvous IDs (RIDs) sent by the broker, corresponding to the address a specific Cloak user client will join to establish a video call session with the bridge. The RID depends on the chosen WebRTC-based carrier application, like a chatroom URL in Jitsi Meet. To demonstrate this process, consider Alice, a user in a censored region using a Cloak bridge located in a free Internet region. To access a website like www.cnn.com via the Tor network in a censorship-resistant manner, Alice obtains the Cloak PT client software and configures her Tor client to use Cloak as the designated Pluggable Transport. When Alice initializes her browser, the Cloak client generates a random RID and password on a chosen WebRTC platform (e.g., Jitsi Meet) and sends it to the broker. The broker selects an available bridge and shares the RID and password with it. Subsequently, the client and bridge join the designated chatroom, ensuring it is password-protected for added security. Through the covert channel established using Protozoa video encoding techniques, Cloak ensures that the WebRTC stream appears as a regular video call, providing robust resistance to traffic analysis attacks.