If you’ve had the need to send secure, private messages in recent times, you might have considered using Telegram. However, using such a service means that, if discovered, it’s well known what manner of encryption you’re using, and there’s a third party involved to boot. [Labunsky] walks a different path, and built a covert channel within Telegram itself.
[Labunsky] likens their process to the process used in the film Seventeen Moments of Spring, in which a flower placed in an apartment windows indicates a spy has failed their mission. In this case, instead of a flower in a window, one user blocks another to signal them. By switching the blocked status on and off, messages can be sent, albeit in a slow and convoluted way.
It’s more of a proof of concept than a practical way to message people over Telegram. With that said, it does work, and it might just keep the security services monitoring your chats confused for a few extra weeks. Or, it would, if we hadn’t written an article about it. Perhaps consider using zero-width characters instead.