signalapp/Signal-Android ? reverse-engineered prompt

I want to build a secure messaging app for Android, basically a clone of Signal. It should be a native app written in Kotlin. The main features are private, one-on-one and group chats. People should be able to send text messages, pictures, and videos, and everything needs to be end-to-end encrypted by default. I also want it to have high-quality, encrypted voice and video calls.

The design should be very clean and easy to use, so people don't have to think about security—it just works. Don't worry about things like stickers or payments yet, just focus on the core secure communication experience. You can use whatever modern Android libraries are best for building a smooth and secure messaging app. Look up current best practices for E2EE if you need to.