[alias_neo]

Actually his comment is quite useful and tells you enough to know notnto use it if security is actually a concern. Without PFS (Perfect forward-secrecy) someone who obtains a key or brutes/reverses one has theoretically unlimited time to do so and gain access to all future communications with that key because the key isn't Ephemeral.

Compared to WhatsApp and Signal that's bad, they both use a well-thought out security model.

As for Telegram, well, Telegram is Telegram.

It's up to the reader to decide what "theoretically unlimited time" means in this case with regards the adversary.