I've been using Threema [1] without any issues, and it works on Android and iOS. The user experience is on par with WhatsApp, I would say. The source is not ava

I've been using Threema [1] without any issues, and it works on Android and iOS. The user experience is on par with WhatsApp, I would say. The source is not available, so you must be willing to take their claims at face value [2]. [1] https://threema.ch/en/ https://threema.ch/en/ [2] https://threema.ch/press-files/cryptography_whitepaper.pdf https://threema.ch/press-files/cryptography_whitepaper.pdf