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Telegram, the supposedly secure messaging app, has over 100 million users. You might even be one of them. If you are, you should probably stop using it right now. Here’s the unfortunate truth about Telegram: it’s not as secure as the company’s marketing campaigns might lead you to believe.

Last update: May 22, 2020
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Introduction
This article analyses the security and confidentiality features of the most commonly used communication services or applications.
Note: the comparison is made between WhatsApp (the most widespread 1.6 billion users), Telegram (the most secure and widespread 400 million users), Signal and Wire (the most secure and confidential) according to world statistics. A comparison in terms of functionality is available at this address.
Remark: for any communication…

WhatsApp, Signal e Telegram promettono tutte la stessa cosa: comunicazioni sicure. Ma ci possiamo fidare?

A reminder, because this sometimes surprises people, and feel free to correct me if the facts have changed recently:

Telegram supports end-to-end encryption only in 1:1 private chats.

End-to-end encryption is disabled by default.

Telegram does not support end-to-end encryption, at all for group chats, its most popular use case.

Instead, Telegram claims that those group chats are "encrypted" by dint of the TLS connection between Telegram clients and the Telegram servers, which can, in this model, read all group traffic.

People like to dunk on the weirdness of the limited E2E crypto Telegram does have; it's archaic and idiosyncratic and people have published research results about it, though none to my understanding are of real practical impact. I support people dunking on bad crypto. But that has nothing to do with why Telegram is an inferior secure messenger.

By comparison, Signal, which Durov has repeatedly talked down:

• has modern, ratchet-based forward secure end-to-end crypto, always, in both group and private messaging;

• won the Levchin Prize, refereed by some of best-known names in academic cryptography, for the design and implementation of that cryptosystem, as well as for its implementation at WhatsApp;

• ha repeatedly foregone basic messaging app features simply to avoid collecting user metadata; Signal didn't even have user profiles until they could figure out a way to implement it in a privacy-preserving manner, and even their GIF sharing feature has a purpose-built anonymity system; we'll only this year potentially get usernames instead of phone numbers because it took that long to design a trustworthy social graph that didn't leave Signal with a giant pile of subpoenable metadata.

Use whatever messaging app you want.