For once, this doesn't rely just on having an internet connection, but also sends and receives messages via WiFi and Bluetooth.
Even better is that it doesn't rely on any one server! It is pure peer-to-peer and fully encrypted. It also has a blog & forum feature and an RSS reader.
You can connect to nearby contacts without the need for an actual internet connection. Damn! If only people had known this when the Hong Kong resistors were organising over Telegram and the authorities knew and people got busted and...don't get me started!
This also makes it a very useful messenger when the internet has been taken down by the government (or others!). On top of this, the setup without a central server makes it impossible for governments and law enforcement to stop the communication flow.
The Briar software is 100% open source but unfortunately only available over f-droid or Google Play, there is no iOS version as of now.
The app was developed by and for activists and journalists but is, of course,ideal for anyone who wants secure communications. The WiFi/Bluetooth connection is based on the principle of a mesh network, so everyone extends the network by using it which in turn extends help to others nearby to join the mesh and exchange encrypted messages.
Briar uses the Tor network to sync when you chose to use an internet connection. Whilst this is optional, why wouldn't you use it ;)
Briar avoids the following censorship & surveillance of messaging, forums and blogs by use of the following:
Metadata surveillance: Briar uses the Tor network to prevent disclosure of users and all contact lists are encrypted and only stored on their own device.
Content surveillance: communications between devices are encrypted end-to-end, protecting all content.
Content filtering: the end-to-end encryption prevents keyword filtering and it's decentralization means that there is single servers to block.
Takedown orders: each user within a forum retains a copy of all posts so that there is no point where a post can be deleted.
Denial of service attacks: forums have no central server to block/hack and each subscriber has access to the content even when offline.
Internet blackouts: can operate over WiFi and Bluetooth to ensure the service can be maintained during blackouts.
Briar combats the following adversarial threats:
Monitoring, blocking, delaying or modifying traffic on long range communication channels
Monitoring, blocking, delaying or modifying traffic on short range communication channels (WiFi, Bluetooth etc.)
The network can't have it's standard cryptographic primitives broken despite access to and usage of it by hostile agents, thereby eliminating their ability to interact or influence regular users.
Briar doesn't support screeenshots which is great as it ensures no-one can get a hold of your phone and forward your conversations, plus it also protects you from screenshots taken on Android.
This is important as Android apps can share screenshots between apps, without the users' knowledge or permission. This is also used for Analytics...we need say no more! Briar blocks this feature, just as Signal and Threema do (well, there is an enabling option in Settings).
I must admit we have only just started to use Briar and keep finding more to appreciate about it daily.
Bold statement but this could be the future of communicating on and offline! Let's hope we see an iOS version soon and perhaps even for desktop as well but in general, there is not much to dislike about this fantastic service.