Telegram is a cloud-based instant messaging, videotelephony and voice over IP service with end-to-end encryption for secret chat only. Telegram client apps are available for Android, iOS, Windows Phone, Windows, macOS and GNU/Linux and originated in Russia in 2013. Users can send messages and exchange photos, videos, stickers, audio and files of any type.
Telegram’s client-side code is free software, whereas its server-side code is closed-source and proprietary. The service also provides APIs to independent developers. As of April 2020, Telegram had 400 million monthly active users. An announcement at that time included a promise to implement secure group video calls later in 2020.The default messages and media use client-server encryption during transit. This data is also encrypted at rest, but can be accessed by Telegram developers, who hold the encryption keys. In addition Telegram provides end-to-end encrypted calls and optional end-to-end encrypted “secret” chats between two online users on smartphone clients. However, the desktop clients (excluding macOS client) do not feature end-to-end encryption, nor is end-to-end encryption available for groups, supergroups, or channels. Telegram has defended the lack of ubiquitous end-to-end encryption by claiming the online-backups that do not use client-side encryption are “the most secure solution currently possible,” despite several other chat services such as Signal, Matrix, and WhatsApp offering end-to-end encryption on all platforms.