My friend and I were discussing cell phone security and he said that if someone backdoored your phone that they could read all your signal messages. Is this true? I would think that the only way to view signal messages is to literally open up the app and view them.
If your phone is compromised, anything that you can see they can see as well. Absolutely nothing can protect against that because the only way would be to prevent even yourself from seeing it.
Potentially a really good sandbox and strict permissions could help, but if someone were to backdoor your phone chances are they can get around most software based solutions anyway.