Let's Encrypt, DNS over TLS and Android
Because of the recent expiry of the certificate used to cross-sign Let's Encrypt certificates, Android gets confused when you try to use them for DoT.
Overview for certificate
Firefox for Android: using a custom certificate authority
How to use your own, self-generated certificate authorities in Firefox for Android
Android 7.1 and certificate authorities: unfortunately, I was being too pessimistic
I wrote a piece about Android 7 and its certificate authority system. Now that Android 7.1 has been released, most of the problems I predicted turn out to be nothing.
Android 7 Nougat and certificate authorities
In this article I will cover some details about the way Android 7 "Nougat" treats user-installed certificate authorities. Android 7 improved security in many ways. However, this has several downsides... As an added bonus, I describe a way to install a certificate authority in Android 7 using root access.