Telegram said in a blog post that the voice calls are based on the same end-to-end encryption methods as its Secret chats feature, but says it has introduced a new "key exchange mechanism" to make sure calls are even more secure.
The key verification UI we came up with in 2013 to protect against man-in-the-middle attacks served well for Telegram (and for other apps that adopted it), but for Calls we needed something easier. That‘s why we’ve improved the key exchange mechanism.
To make sure your call is 100% secure, you and your recipient just need to compare four emoji over the phone. No lengthy codes or complicated pictures!
Whenever possible, calls go over a peer-to-peer connection, "using the best audio codecs to save traffic while providing crystal-clear quality", according to Telegram. If a peer-to-peer connection can't be established, the closest server to the user is connected to instead.
Once a voice call is made, a dedicated tab for calls appears on the main screen of the app. The Voice Calls feature rolls out in Western Europe today, with the rest of the world to get them "very soon".
In addition to voice calls, the latest v3.18 version of the app also offers users direct control over the quality of videos shared over the platform. Telegram remembers the compression rate once it has been selected, and uses it as the default setting for future video uploads.
Telegram is a free download for iPhone on the App Store. [Direct Link]