I'm not knowledgeable about this -- is signal's e2e encryption even viable for a service with N users, and one where new users are being added?

Put another way, if I have a group with 10 users and it's encrypted and then another person joins and can see the old messages, was it actually securely encrypted in the first place?

> if I have a group with 10 users and it's encrypted and then another person joins and can see the old messages, was it actually securely encrypted in the first place?

Sure, why not? Assume, just because it's the first thing that came to mind, that message history is encrypted using GPG and every message is encrypted with everyone's individual public keys. When a new user joins, one user just encrypts the message history with the new user's public key.

Or am I missing something? Do the existing users in the group not have access to their own message history?

You’re not missing anything, this is definitely possible to do.

That said, encrypting every message with everyone’s public key doesn’t scale, so instead you’d likely want to generate a symmetric key for the group and as new users are invited the inviter would encrypt the group key with the invitee’s public key. That makes it trivial for new users to view history, and as new chats are posted they only need to be encrypted with one key.

I don't think Discord gives people access to past message history when joining a group. I don't know of any limitations of Signal's group chats that would be a problem for Discord's group chat behavior.

It does give access to past messages.

Discord support chat history sever side searches, they even posted a blog about how to optimise ElasticSsearch clusters.

E2E encryption is useless here. Unless you setup some kind of dedicated channel for secretive group chats.

It is one of the permission settings that can be toggled for a Discord chat room.

On the other hand, I think they are trying to avoid the less nice usecases of communication by restricting themselves to gaming.

Less nice technically or socially? Speaking as someone who has played countless hours of competitive video games in my downtime after work, I assure you that, socially, 'less nice' is a charitable way to describe gaming chat, devolving into a constant torrent of abuse and harassment depending on your skill level, the sound of your voice, and the Dunning Kruger level of yourself and your other team members.

Discord is already being heavily used in the less nice gaming communities revolving around cheating, compromise/hacked accounts (not just game) selling/malware and game related phish/keylog.

But incidentally the same people selling hacked spotify and netflix accounts also provide "support" over skype, so opsec, meet window I guess