WhatsApp is opportunistic encryption by default, trusting the server to provide it keys. Pretty much nobody turns on showing when someone's key changes, and if

WhatsApp is opportunistic encryption by default, trusting the server to provide it keys. Pretty much nobody turns on showing when someone's key changes, and if you do and you verified each 's keys, the server can still learn the plaintext of at least one message by changing keys right when you send a message. Which is a very tiny risk, but it's just not what one would expect. It's as if your browser would continue loading a page with an invalid HTTPS certificate and show you a warning afterwards -- and only if you turned on showing that warning in the settings. Even if you turn it on and you're not afraid of the server swapping the key when you send a message (which is fair enough), do all your contacts also have it turned on? And would they tell you immediately and out of band (otherwise the attacker can suppress or change the message) that they saw your key change? But an even bigger reason I don't have whatsapp is because of Facebook. Metadata has already been mentioned by others so I won't repeat that.