[jonesnc]

Isn't the Signal Protocol an open protocol?

https://signal.org/docs/ and https://en.wikipedia.org/wiki/Signal_Protocol#Implementation...

[aborsy]

The platform (smartphone) is a proprietary, insecure black box. Lately, vendors are brining client side scanning to phones too.

With PGP, you can take your message anywhere, to any OS, client software and with any encryption key and algorithm you like, to encrypt it.