Silence

Signal is a protocol, there are other implementations of the client, for instance; Silence[1]. Which is a fork of TextSecure (now Signal) that aims to keep the SMS encryption that TextSecure removed for a variety of reasons. "Protect your communication in transit and on your phone. Silence[2] (formerly SMSSecure) is a full replacement for the default text messaging application: all messages are encrypted locally and messages to other Silence users are encrypted over the air." [1] https://github.com/SilenceIM/Silence [2] https://silence.im/

Android as a fork of TextSecure called Silence https://github.com/SilenceIM/Silence but the metadata would be easily accessed when sending encrypted sms. While the contents of the message may be secure who and when you were talking would be easily accessed.

Just in case, do you know about https://github.com/SMSSecure/SMSSecure?

But what about the fork https://github.com/SMSSecure/SMSSecure which can be installed on via f-droid google-less phone?

Actually, if you receive a message from someone using SMSSecure, you'll get a prompt asking if you want to upgrade to a secure session. But yes, there is no way to look someone up and check if they're using SMSSecure. The detection was actually inherited from TextSecure and works by "tagging" shorter messages with some detectable whitespace after the message contents. A bit of a hack, but it's a limitation of the transport. Relevant commit: https://github.com/SMSSecure/SMSSecure/commit/93d94f2b7a9fd6...