ChatSecure-iOS VS OnionShare

iOS: ChatSecure [No Tor connection? That I don't know.]

In this case, I would rather suggest others to use the likes of Element a Matrix client, or e.g. RetroShare, Briar, OnionShare, or e.g. XMPP with the clients like Dino, Conversations, Gajim, ChatSecure.

ChatSecure

onionshare.org is p2p over the tor network, so very private but such a large file would strain the network

OnionShare is a multi-purpose tool that allows you to send and receive files and messages over Tor. I think this might be more aligned with your purposes, but with the caveat that this is a Tor-specific option (if I'm not mistaken).

By default, it'll install the Onionshare utility to help with launching/managing some of the most common use cases for onion services. (You can also toggle it to NOT install by modifying deployment variables) You can find more in-depth instructions and deployment guides in the project's README file.

Briar is one of the most important secure messaging projects currently. Not only does it remove the need to trust the vendor about content (like with all E2EE messaging apps), you also get to keep the metadata about communication to yourself as data transits from one Tor Onion Service to another.

The downside is of course, you need to keep the endpoint powered on when you want to be reachable so it will increase the battery drain on your phone.

Note: There's also a desktop client if that's easier to keep online https://briarproject.org/download-briar-desktop/

One extremely important thing Briar is doing, is it's using the P2P as means to host alternative social interaction formats, like forums and blogs. Similar to Signal/WhatsApp stories (which is somewhat similar to microblogs/FB wall), it's a way to indirectly share information. You could pretty much emulate any social media platform on top of E2EE protocol with ~zero infrastructure cost and without having to worry about data mining. I'd argue what Briar's innovating on here is one of the most important aspects in what's left for secure messaging.

Finally a small caveat: Briar will share your Bluetooth MAC address with all peers so it can automatically use that when you're in close proximity with your peer. Thus sharing your Briar ID publicly is not a good idea for two reasons:

1) major global adversaries may have access to that information (e.g. if Google aggregates it) which can deanonymize your account. This also allows slightly technical person to confirm identity of briar account if they suspect it's you (a bit wonky threat model but still).

2) it ties everything you do across your accounts on same device together, so there's strong linkability even if you rotate the identity key by reinstalling the app.

Briar is pretty clear about this in it's FAQ, but it's still not very well known although it definitely should be.

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That being said, if you want similar Onion Service based communication with no such linkability, there's https://cwtch.im/ which is a fantastic project.

There's also https://www.ricochetrefresh.net/

Both are spiritual successors to John Brooks' `Ricochet` application.

You can also chat and share files (among other things) with https://onionshare.org/

(And finally, you can get remote exfiltration security for keys/plaintexts with TFC https://github.com/maqp/tfc (my personal work), at the cost of losing some features like message forwarding etc that the architecture prevents you from doing.)

You can chat on https://onionshare.org/

Small atom machine running this: https://onionshare.org/

Onionshare if you want to share it anonymously. It would be really slow on the scale of three terabytes though.