Does anyone know an open source secure communication software for android?

Question

Android

Does anyone know a program for android devices for secure communication.
Required conditions:

1. open source software
   
2. support for OpenPGP encryption or other
   
3. it is desirable to have file sharing
   
4. the main thing is that it is possible to send encrypted messages to each other even when the interlocutor is offline and that the history of correspondence is saved. That is, so that the interlocutor can enter online and decrypt the message sent to him.
   

I use something similar now - this is the Conversations jabber client from the developer Daniel Gultsch, which supports encryption via OTR, but the problem is that when sending a message to an offline interlocutor, the text comes in unencrypted form. As far as I understood correctly, working with the OTR protocol is possible only when both interlocutors are online. The program also has the ability to encrypt messages using the OpenPGP protocol, but for this you need to download a separate OpenKeychain application. Unfortunately, I have not been able to find instructions for setting up the joint work of these two programs for full encryption through OpenPGP. Maybe someone did it and he will share his experience.

Answer 1

If you need end-to-end encryption + file transfer + openness, I think "Telegram secure chat" will do. If PGP is still urgently needed, then something tells me that setting up Conversations in conjunction with OpenKeychain will not be difficult, since integration is declared on Google Play, you just need to go to the developers' github: ( https://github.com /siacs/Conversations):

How do I use OpenPGP
Before you continue reading you should note that the OpenPGP support in Conversations is experimental. This is not because it will make the app unstable but because the fundamental concepts of PGP aren't ready for widespread use. The way PGP works is that you trust Key IDs instead of JID's or email addresses. So in theory your contact list should consist of Public-Key-IDs instead of JID's. But of course no email or XMPP client out there implements these concepts. Plus PGP in the context of instant messaging has a couple of downsides: It is vulnerable to replay attacks, it is rather verbose, and decrypting and encrypting takes longer than OTR. It is however asynchronous and works well with message carbons.
And now the main thing: Security must be approached comprehensively. If you use Faceboogle services, sit on Windows (that is, you trust it, but don’t you trust telegrams?), Work in a broken Photoshop, receive files that you plan to send using a secure messenger through public mail services, and not through your own mailer with PGP, and also store those files in the clouds, it makes no sense to have one dedicated piece of your workstation protected - not a concept. I'm not talking about the fact that your chat correspondent is obliged to carry out a similar set of measures and not send the received files to anyone by open mail / to the cloud / etc. And this is all just the tip of the iceberg.

Answer 2

https://www.eff.org/secure-messaging-scorecard