For open source messengers, you can check whether they actually encrypt your messages and whether the server has access to your encryption keys but what about WhatsApp? Since it’s not open source, you can’t be sure that the encryption keys aren’t sent to the server, right? Has there been a case where a government was able to access WhatsApp chats without reading them from the phone itself?
The keylogger and operating system (if you’re using Android) is open source as well. They can’t just put a keylogger in there.
Nah, the OS has proprietary overlays that vendors put in there. And it’s not like you’re reviewing and compiling your own software - you’re dependent on your provider to be honest with the software they actually installed. But factually you have no idea if the android phone you purchased has been modified. And Android itself is so huge that backdoors can be sneaky. We have already caught several instances of attempted backdoors in Linux - but there’s always the fear we didn’t find them all
If this all sounds way too paranoid, then review Snowden leaks