At uni, it's common to have whatsapp groups for classes, which tend to be encrypted 100 to 200 people WhatsApp groups.
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How important is it for these kind of groups to be E2E encrypted though? If you're sending a message to 100 people then you probably ought to consider it de facto public even if only the intended recipients receive it.
Partly "middlingly important" because yes, it's kinda effectively public.
But also: why the heck wouldn't you want to encrypt it? The existence of leaks doesn't make basic prevention useless.
How many of those have verified all the public keys? If you never do verification e2ee is basically meaningless.
"You can fool some people sometimes, but you can't fool all the people all the time."
If you don't verify the keys, e2ee is basically meaningless against targeted surveillance. As long as some fraction of people verify keys, it is still effective against mass indiscriminate surveillance.
how is e2e better against mass indiscriminate surveillance than just normal TLS? The only time when e2e is meaningfully different then https is when the server you're talking to (i.e. your personal matrix homeserver) is compromised. In that case, aren't you already in the realm of targeted surveillance?
Some homeservers are larger than others (e.g. matrix.org). They don't all need to be compromised to enable mass surveillance. It also depends on where TLS is terminated. If you're running a homeserver on AWS or something behind their load balancer, there's a difference.
Generally, I'd argue that E2EE provides defense in depth against "unknown unknowns" if server infrastructure is compromised by any means. Although I do acknowledge it adds one more level of complexity, and often another 3rd party dependency (presuming you're not going to roll your own crypto), so it's not a strict positive.
> The only time when e2e is meaningfully different then https is when the server you're talking to (i.e. your personal matrix homeserver) is compromised.
Only if everyone's running their own personal homeserver, which seems pretty unlikely for regular people. You could've said the same thing about email (it's not meaningfully different unless your personal email server is compromised), but in reality the NSA ran mass surveillance on gmail and picked up a lot of data that way.
Serious question, if a surveillance organization had control of a certificate authority trusted by your client, would that allow them access to traffic whose security relied on a certificate from that authority?
By that logic the vast majority of users of whatsapp, signal and most other e2ee protocols/apps use it in a useless way, right? Most people I know who use these apps (even the security-conscious ones) never verified the key.
Signal tells you outright when someone's key has changed, though. It's usually pretty trivial to establish that the original conversation is authentic when you're just talking with people you know in real life (where an impersonation attempt would likely fail for numerous reasons), and you can assume that device is still theirs until their key changes.
There is still a risk that someone is running a MITM attack. The initial conversation would be authentic, but the key belongs to someone else who is just forwarding the messages. Your communications would no longer be private and they could switch from passive eavesdropping to impersonation at any point without changing the key.
Most people rotate their Signals keys every time they rotate their phone hardware (which is inexplicably often for some people apparently), because keys are just auto-accepted everywhere so there is no real incentive to bother moving them. In larger groups there's always someone.
It isn't helped by the fact that the backup process is a bit obscure and doesn't work cross operating systems. For the select few that cares, verifying keys is effective against attackers who aren't Signal themselves, Google or in control of the Play Store. Just make sure to keep an eye out for that key changed warning, it's easy to miss.
It used to tell you. Does it, still?
Yes
Yes, pretty much.