[Cryptography] WhatsApp: Why asymmetric key instead of symmetric keys?

[Ismail Kizir]

Hello,

I am not sure, but as I understand from what I read on Internet,
WhatsApp exchanges asymmetric keys, even when two user are
face-to-face and they scan each others qr-code.
Isn't it a "bad logic"?

When two users are physically together and they can scan each other's
symmetric keys via optic qr-codes, without the risk of compromise, why
they still insist to use asymmetric keys?

For one year, I've been working on a similar project, and I have both
asymmetric key and symmetric key exchange protocols. And I am sure
WhatsApp could(should) do the same thing.

Am I wrong? Or did I misunderstand their key exchange protocols?

Regards
Ismail Kizir