Recently there have been a lot of news articles which say that Facebook will very soon add advertising to WhatsApp, yet will keep the end-to-end encryption (source):
[M]essages will remain end-to-end encrypted. There are no plans to change that.
I am trying to understand how advertisement is possible while keeping end-to-end encryption. I understand that there are several options:
Advertisements are not targeted according to words used in messages, just general ads.
It is possible to send additional/duplicate packets with the same information to the server, which also uses "end-to-end encryption". Yet, if that's the case, it's sort of "telling the truth but not all the truth". I find it hard to believe that such a method would be used.
Are there other ways to do both ads and e2e encryption that you can think of?