It's hard for me to believe that people actually think they can use Signal or some other 'security app' on a device that is fundamentally compromised already.

Sure, your messages are encrypted, but they (whoever they are) have the private keys (both sender and receiver) because the smart phones you are using are compromised by them.

It's really simple.

So next time you read a news story about criminals who were using some supposedly secure app to commit crimes, but got caught anyway... keep this in mind.