Standard primitives, perhaps, but has the scheme itself been reviewed by competent cryptographers?
At best, the Telegram developers are well meaning but have demonstrated in previous versions of MTProto that they lack a background in cryptography or a desire to consult experts. And their public face—posts like this one—seem often to be hyperbolic attacks on competitors, which is not a great look.
I’m not a cryptographer, so I’m not going to review the current MTProto. I hope it’s awesome and bug-free. But some skepticism seems warranted.
Does Telegram use end to end encryption by default yet, or does it still send and store everything except for secret chats to the Telegram service in plaintext?
Also, when you use the secret chat feature does that now support multiple clients or does it still establish a secret chat with a random recipient client over which neither initiator nor receiver can control?
Telegram crypto was redone, and is now using standard primitives. You can verify it at high level at https://core.telegram.org/mtproto or low level if you'd like to check sourcecode in their github. BTW, telegram has reproducible builds since last year.
I'm tired of people repeating 7 years old meme without verification.