Telegram is a cloud
-based Instant Messaging
and Voice over IP Service Provider
Telegram's Client-side code is Open Source software whereas its server-side code is closed-source and proprietary. Telegram service also provides APIs to independent developers.
Telegram uses a Symmetric Key Cryptography scheme called MTProto. The protocol was developed by Nikolai Durov and other developers at Telegram and is based on AES-256 Symmetric Key encryption, RSA 2048-bit encryption and Diffie-Hellman key-exchange.
Telegram's Messages and media in Telegram are encrypted when stored on its servers, and the client-server communication is also encrypted
Telegram service provides End-to-end Encryption for voice calls, and optional End-to-end Encryption for "secret" chats between two online users, yet not for groups or channels.
Telegram Digital Identity of End-User's are bound by to Phone Numbers and are verified by SMS.
Telegram has some other projects:
There might be more information for this subject on one of the following: