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Comment by daurnimator | Hacker News Reader

I've been working on a new scheme for decentralised encrypted (group) messaging bus over at https://xn--nma.com/ unlike many other schemes, forward secrecy is not a goal: When I invite a friend to a group chat, I want them to be able to obtain historical conversation messages.

For your normal end user (at least what I think of as common: see how facebook messenger works, as well as slack, discord and even how many irc chat rooms have public logs), how is this MLS scheme useful?

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Interesting, I actually wrote 'ȱ.com', hacker news seems to expand to punycode.

If you don't need PFS you could probably modify MLS to be a bit simpler.

Firstly, no need for sender keys. A single group key will do. When you remove someone from the group, you still do the group update and derive a new group key (unless you don't want post-compromise security either, in which case you can throw out the entire tree concept).

Now when you add someone to the group, you share with them the entire historical group transcript along with all the previous group keys.

Is this roughly what you're looking for?

Are you aware of matrix? Their olm encryption scheme is capable of PFS, but it's not used exactly in order to provide history.

Yes I'm aware of matrix. A couple of things that I don't like about the matrix protocol are: 1. identity is tied to a server and users are not free to move between servers. 2. servers are assumed to be always online and have low latency.

1. There is work to fix the identity problem with Identity Servers. See https://matrix.org/faq/#what-is-an-identity-server%3F

2. I'm not sure what gives this impression? I have a server that is very much on flaky network, and it federates just fine. The point is that servers can go online/offline without breaking anything on the whole network.

There is a proposal for decentralized user accounts: https://github.com/matrix-org/matrix-doc/issues/915

There's also megaolm. Megaolm seems to be scaling better than other production setups, in practice.

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