>But a bad crypto implementation will work. For all intents and purposes, it will appear completely fine. Users will get their messages. The bitstream will appear completely random. At least, until somebody with expertise in breaking crypto systems digs into it.

And that applies even if they're using AES but wrong mode of operation. That applies even if they're using best practices like AES-GCM but the CPU doesn't support AES-NI and a cache timing attack allows key exfiltration.

Like Swiftonsecurity wrote:

"Cryptography is nightmare magic math that cares what kind of pen you use. Should math care what kind of pen you use to implement it? No, but Fuck You, this is Cryptography."

The attacks are incredibly subtle for even the best systems, and Telegram is so far away from even adaquate it's difficult to emphasize it so I'll try with my best restraint:

TELEGRAM FUCKING LEAKS EVERY GROUP MESSAGE TO THE SERVER WHICH IS THE EXACT EQUIVALENT OF A FUCKING BACK DOOR.

I hope that didn't leave anything unambiguous.