We at Telegram love to build sophisticated technologies that combine speed with security. Starting with Telegram 4.2, we support CDN caching. CDNs are third-party caching nodes that we’ll use to cache publicly available videos and photos posted in massive channels (say, with 100,000+ subscribers) for users in remote locations where Telegram is popular.
This will increase download speeds for tens of millions of users as CDN caching allows data to travel shorter distances and helps avoid bottlenecks that exist between regions.
While these caching nodes are only used to temporarily store public media (imagine Telegram versions of superpopular YouTube hits), all data that goes through them is encrypted with a key unknown to the caching nodes. In other words, we treat these CDN caching nodes just like we treat your internet provider – they only ever get encrypted junk they can't decipher.
If you're interested in the technical details, feel free to check out this page that describes the relevant encryption and security checks. And as always – the updated source code for the Telegram apps is open and available for your scrutiny. Security experts are welcome to verify the implementation of CDNs based on the open source code we make available for all of our apps.
Thanks to this technology, the download speed for public photos and videos in places like South America, Turkey, Indonesia, India, Iran or Iraq will significantly increase without the slightest compromise in security.
Stay safe (and fast)!
July 23, 2017
The Telegram Team