Encrypted messaging app and WhatsApp rival, Signal has announced that it now supports 40 participants on group video calls. The company said that it launched end-to-end encrypted group calls a year ago, and since then it has increased its support for five participants to 40. “There is no off-the-shelf software that would allow us to support group video calls of that size while ensuring that all communication is end-to-end encrypted, so we built our own open-source Signal Calling Service to do the job,” the company said in a blog post.
Signal now supports 40 person group calls. Building large end-to-end encrypted group calls required some new engineering. Learn how we did it here: https://t.co/i27rRqkI4l
— Signal (@signalapp) December 15, 2021
To Increase Group Video Calls Limit, Signal Assessed Open Source SFUs
Furthermore, Signal stated that when developing support for group video calls, it assessed many open source Selective Forwarding Unit (SFUs), but just two had acceptable congestion control. “We launched group calls using a modified version of one of them, but shortly found that even with heavy modifications, we couldn’t reliably scale past eight participants due to high server CPU usage,” the company said.
Signal Wrote a New SFU from Scratch in Rust
To scale to more participants for group video calls, the company wrote a new SFU from scratch in Rust. It has now been serving all Signal group calls for nine months, scales to 40 participants with ease, and is readable enough to operate as a reference implementation for an SFU based on the WebRTC protocols, the corporation said.
In addition to this, the encryption keys are also necessary to secure the calls also continue to come from user devices, not from the servers. “When a client joins the call, it generates a key and sends it to all other clients of the call over Signal messages,” the Signal Foundation continued. “Whenever any user joins or leaves the call, each client in the call generates a new key and sends it to all clients in the call. It then begins using that key 3 seconds later.”
Read more: Signal Rolls Out In-App Sustainer Program to Receive Donations from Users
