I want to use SMS authentication safely, so I am looking for an SMS app that has SMS encrypted properly. Please tell us the Android and iPhone apps. Make sure your app is open source.
I don’t think there is a way to do that because I haven’t seen anything about forcing the SMS authentication message sender to use anything but plain plaintext SMS.
As @BearerOfHonesty mentioned, apps like Silence require both parties to use this app. For encrypted messaging, a key exchange is necessary. So, you don’t get any encryption or additional security by just switching your SMS app to Signal, Silence etc.
You could maybe try GPG over SMS, not sure if the recipient likes to use it though, but it would do the job.
So it’s kind of like Briar, then? Actually, the newest release of Briar doesn’t require you to meet up in person. I’m trying that out with some of the forum members here.
You don’t have to meet in person to use Signal or Silence. The key exchange is possible over the internet. However, if you (for instance) use Silence on your device and your remote friend uses SMS app xyz, then you can’t use Silence’s encryption feature. Your friend also has to install Silence to allow encryption.
This is true. It is also true for Signal. And Signal will never encrypt SMS at this point.