Let’s Reverse Engineer Telegram: How MTProto & Secret Chats Actually Work

How Telegram Works Under the Hood: Breaking Down MTProto, Secret Chats & More

In a world where tech giants often misuse our data for their own gain, Telegram stands out as a rare exception. Owned by Pavel Durov, Telegram isn’t just another messaging app—it’s a platform that has redefined what secure, fast, and feature-rich communication looks like. From end-to-end encrypted secret chats to powerful features like channels, bots, and multi-device sync, Telegram proves that messaging can be both functional and private.

So, how exactly does Telegram work behind the scenes? What makes it faster and more secure than the rest? Let’s break it all down—from architecture and protocols to encryption and reverse engineering.

 Telegram at a Glance: Speed Meets Security

Telegram is a cloud-based messaging platform known for its speed, security, and seamless cross-device experience. Unlike most messaging apps that rely on standard security protocols like TLS (Transport Layer Security), Telegram created its own protocol called MTProto (Mobile Transport Protocol). MTProto is optimized for unstable or low-data networks, making Telegram perform better even under poor internet conditions.

Example: Ever noticed how Telegram still sends messages smoothly even when your mobile data is weak? That’s MTProto doing its magic.

 Telegram’s Server Architecture: How It All Connects

Telegram uses a client-server architecture. Your device (Android, iOS, or desktop) communicates with Telegram's globally distributed data centers. All your regular chats, media files, and user metadata are stored in Telegram's cloud infrastructure.

This setup means:

  • You can access your messages from any device.

  • Chats and media are synced in real-time.

  • But... it also raises some valid concerns about data privacy.

At this point, you might ask:

“Wait... are even my secret chats stored on Telegram’s servers? What if my private messages are compromised?”

Let’s answer that with a closer look at the two types of Telegram chats.

 Cloud Chats vs Secret Chats: What's the Difference?

 Cloud Chats (Default Chats)

By default, Telegram uses Cloud Chats. These are not end-to-end encrypted. Instead, messages are encrypted between your device and Telegram’s servers, then decrypted and stored in the cloud.

Key benefits:

  • Seamless access across devices

  • Media and chat history are backed up automatically

  • No need to worry about local storage

However, this means Telegram technically can read your messages, though they claim to store everything securely using server-side encryption.

 Secret Chats (True End-to-End Encryption)

For complete privacy, Telegram offers Secret Chats, which are end-to-end encrypted (E2EE). Messages in these chats are:

  • Encrypted on your device

  • Decrypted only on the recipient’s device

  • Not stored in the cloud

  • Unsyncable across devices

Extra privacy features:

  • Self-destruct timers

  • No forwarding

  • No screenshots (on some platforms)

Secret Chats use strong cryptographic protocols like Diffie-Hellman key exchange and AES-256 encryption in IGE (Infinite Garble Extension) mode to secure your messages. So, even Telegram can’t read them.

Think of it like this: Cloud Chats are like Google Docs—stored online and accessible anywhere. Secret Chats are like a handwritten letter that self-destructs after being read—only you and the recipient ever see it.

MTProto Protocol: Telegram’s Custom Crypto Engine

Here’s what truly sets Telegram apart—its custom-built protocol, MTProto.

 What Is MTProto?

MTProto is the backbone of Telegram’s messaging system. Unlike WhatsApp or Signal that use standardized protocols (like Signal Protocol), Telegram built MTProto from scratch to maximize speed without compromising security.

 MTProto Versions

There are two versions:

  • MTProto 1.0 – Used in older clients; now deprecated due to security concerns.

  • MTProto 2.0 – More secure, modern, and currently in use.

 MTProto's 3 Layers Explained

1️⃣ Transport Layer

Handles the physical delivery of packets between clients and Telegram servers.

Supports multiple transport methods:

  • TCP (443 or 80) – Primary method, works like HTTPS

  • UDP + HTTP – Optimized for mobile networks

  • WebSocket – Used in web apps and proxies

All messages are sent as binary containers, padded to prevent traffic analysis.

2️⃣ Cryptographic Layer

This is where encryption happens.

  • RSA is used for the initial handshake and key exchange.

  • After authentication, both client and server create a shared authorization key.

  • All future messages are encrypted with AES-256 in IGE mode.

  • A SHA-1 hash ensures message integrity.

Here’s how a message is encrypted:

EncryptedMessage = AES_IGE(AuthKey, PlainMessage + SHA1(PlainMessage))

Each device session uses a unique auth key, so your account’s encryption context is isolated per device.

3️⃣ Message Layer

This layer manages how messages and media are structured and delivered.

Features:

  • Bundling: Multiple messages in one container for efficiency.

  • Message IDs: Unique 64-bit IDs to track and prevent replay attacks.

  • Acknowledgment system: Ensures delivery is confirmed.

  • Replay protection: Prevents attackers from resending old messages.

Telegram Bots: Do They Use MTProto?

Nope. Telegram bots don’t use MTProto.

Instead, they use the Telegram Bot API, which is based on standard HTTPS.

  • Developers create bots via tokens

  • Bots receive JSON updates

  • Bot communications are not end-to-end encrypted

  • Easier to reverse engineer and analyze

This makes Telegram bots highly flexible—but less private.

If You want to Reverse Engineer Telegram: Where to Start?

Telegram’s Android app is open-source, giving you a great head start.

Here’s what you need to begin:

 Tools of the Trade

Tool Purpose
jadx Decompile Android APK to view Java/Kotlin code
apktool Decode AndroidManifest, resources, and smali code
Frida Hook into runtime functions; bypass security checks
Burp Suite / mitmproxy Intercept network traffic (needs cert pinning bypass)

 For iOS:

  • Use a jailbroken device or re-sign the IPA

  • Hook into app functions with Frida or Cycript

  • Explore TDLib (Telegram Database Library) – C++ library that powers Telegram client-side logic
    👉 GitHub: tdlib/td

Here's My conclusion:

Telegram is a rare mix of privacy, speed, and developer openness. Its unique MTProto protocol, paired with options for both cloud convenience and true E2EE, makes it one of the most fascinating messaging platforms to study.

Whether you're a cybersecurity student, a reverse engineer, or just curious about how secure messaging really works—understanding Telegram’s architecture, encryption layers, and chat models is an essential step in your learning journey.

So next time you’re messaging on Telegram, remember—you’re not just chatting. You’re using one of the most technically advanced communication systems in the world.
And if you enjoy reading contents on computer science, cybersecurity and Reverse Engineering make sure to follow me for more future updates


Comments

Post a Comment

Popular posts from this blog

Top Linux Distributions for Cybersecurity & Ethical Hacking: A Complete Guide

Image
  The Best Linux Distros for Cybersecurity and Ethical Hacking If you've ever wanted to step into the world of cybersecurity, mastering a Linux-based OS is essential. The reason? Linux is open-source, meaning users can modify the code to suit their needs. However, choosing the right Linux distribution (distro) can be overwhelming due to the sheer number of options available. Below is a  curated list  of the best Linux distros specifically designed (or adaptable) for cybersecurity, penetration testing, and privacy. Each OS has its  pros and cons , and the  difficulty level  varies based on your familiarity with Linux and security tools. 1. Kali Linux Overview: Kali Linux is a popular  Debian-based  Linux distribution developed by  Offensive Security . It comes preloaded with hundreds of penetration testing tools, such as  Nmap, Metasploit, Wireshark, and Burp Suite . It is widely used for  ethical hacking  and  penetration ...
Read more

Ghost Laptop: The Ultimate Privacy-Focused Computer for Ethical Hackers & Journalists

Image
The Ultimate Guide to Building a Ghost Laptop for Privacy & Security Introduction If you're an aspiring ethical hacker , cybersecurity enthusiast, journalist, or just someone who values online privacy , then you've likely wondered: How do I stay completely anonymous online? The answer? A Ghost Laptop —a system built for security operations, privacy, and zero tracking. But before we proceed, let me clarify: This guide is purely educational. Modifying your laptop may void your warranty, and unethical use can land you in legal trouble. Always abide by the law. Now, let’s debunk a common myth—those flashy RGB gaming laptops you see YouTubers promoting aren’t the best choice for privacy-focused operations. Many influencers push these products for affiliate marketing , but that doesn’t mean they are ideal for cybersecurity work. Sure, you need a decent laptop for academic and creative tasks like video editing and presentations, but when it comes to security operatio...
Read more

What is Engineering? and who are Engineers?

Image
What Is Engineering, and Who Are Engineers? Imagine a pleasant Sunday morning: you and your friends have planned a motorcycle ride. Your alarm goes off at 5:00 AM, and you groggily drag yourself into the shower. After breakfast, you hop on your motorcycle, receive a call from a friend, and join the group ride. As you travel, you admire the natural beauty around you and wonder how people constructed that magnificent bridge. Later, while refueling, you spot an airplane flying overhead. All these experiences are the results of engineering. **Engineering Defined:** Engineering is a branch of science that applies mathematical principles and the laws of science to real-world problems. Engineers are problem solvers—individuals who use their knowledge and creativity to design, build, and improve the world around us. **Everyday Engineering:** Think about your day: your alarm clock was programmed by engineers to help you wake up early. Your motorcycle was meticulously crafted by auto...
Read more