IMO, if/when Autocrypt v2 is implemented, Signal, SimpleX, and Delta Chat will all essentially be first-class secure messengers, in the sense that:
- each one has a clear & distinct target demographic and use-case
- there will be only deliberate tradeoffs between them, not omissions of important security features.
(Session and Threema both fail point #1 because Session is a worse SimpleX and Threema is a worse Signal.)
Delta Chat I think is interesting because it (again with a future PFS/PQC update) seems to approach the confidentiality properties of Signal and SimpleX without relying on something like Signal’s centralized infrastructure or SimpleX’s considerably more complicated routing architecture.
The biggest concern I have with SimpleX is that despite the decentralized model I do not see how it could continue to exist without SimpleX the company behind it. Essentially all of the complexity of SimpleX is placed upon the client, to achieve important privacy properties (absolutely minimizing the metadata the servers get) at the expense of being a
Usually where federated projects shine is decentralization of the project as a whole, because different aspects of the project are delegated more appropriately. If I want to develop a Delta Chat client I don’t need to understand and implement server-side things like intra-server routing etc., and vice-versa. And if I am a user of the messaging service I do not need to be responsible for every aspect of my experience: I think this is where a lot of people stop using SimpleX because having the client itself do everything comes with a lot of UX problems that tend to drive people to Signal.
Anyways, it is basically the classic Centralized (Signal) <> Federated (Delta) <> Decentralized (SimpleX) spectrum we always end up seeing in pretty much any field, with the same benefits and tradeoffs these architectures always have. Like with Twitter/Mastodon/Nostr, or Dropbox/Nextcloud/Syncthing, etc.