Telegram MTProto Protocol Explained: How Telegram Encryption Works

MTProto (Mobile Telegram Protocol) is Telegram's custom communication protocol. It handles all data transmission between Telegram clients and servers.

MTProto Architecture

MTProto operates at three layers:

High-level: API queries and responses (the methods you call).
Crypto layer: Encryption, message authentication, key exchange.
Transport layer: TCP, HTTP, or UDP connections to servers.

Encryption in Regular Chats

Regular (cloud) chats use client-server encryption. Messages are encrypted between your device and Telegram's servers using a combination of AES-256, RSA, and Diffie-Hellman key exchange. The servers decrypt, re-encrypt, and forward to the recipient.

Encryption in Secret Chats

Secret Chats use end-to-end encryption via MTProto 2.0. The encryption keys are exchanged directly between devices using Diffie-Hellman key exchange, and messages are never stored on servers. Even Telegram cannot read Secret Chat messages.

MTProto 2.0 Improvements

MTProto 2.0 (introduced in 2018) added several security improvements:

SHA-256 instead of SHA-1 for key derivation.
12-1024 bytes of padding instead of 0-15 bytes (better protection against length-based attacks).
Improved key verification process.

Criticism and Debate

Cryptographers have debated MTProto's security because it is a custom protocol rather than a widely-reviewed standard (like the Signal Protocol). Telegram has responded by publishing the full specification, offering bug bounties, and hosting cryptography competitions.

Frequently Asked Questions

Is MTProto as secure as the Signal Protocol?

The Signal Protocol is more widely reviewed by cryptographers and is considered the gold standard for end-to-end encryption. MTProto uses non-standard cryptographic choices. However, no practical attacks against MTProto 2.0 have been published. The key difference is that Signal applies E2E encryption to all messages by default, while Telegram only uses it for Secret Chats.

Why did Telegram create its own protocol instead of using Signal Protocol?

Telegram designed MTProto to optimize for speed and reliability on mobile networks. It prioritizes fast message delivery, cloud sync, and seamless multi-device support, features that are harder to implement with strict E2E encryption. Secret Chats use E2E when maximum privacy is needed.