Since 2015 ProtonMail’s web app has been open source, and today the company announced that its iOS app is, too.
In addition to making our iOS app open source, we have also documented and published our iOS security model. This is important to us because raw code without documentation can be almost unintelligible sometimes, and a documented security model will assist in rigorous assessment and review of our code by the public. Our iOS trust model is also available on our Github page.
Check It Out: The ProtonMail iOS App is Now Fully Open Source