WhatsApp could exfiltrate messages at the ends. But I assume the trick lies in the word "default". Didn't Skype also default to end-to-end encryption, unless there was a server flag that disabled it for that specific user (I might be fuzzy on the details)
> Whatsapp used to have this, but lately they have cracked down on third party clients.
Blame spammers on that. The amount of scammers and spammers on Whatsapp is unreal.
If there is a 2nd opensource client written by someone else, you would hope they would raise the alarm when asked to implement "feature flag 437 means send all the crypto keys to the server".
I don't trust un-auditable client applications...
If you want to assure me your e2e is secure, there must be at least two clients implemented by different people, with at least one of them opensource.
Whatsapp used to have this, but lately they have cracked down on third party clients.