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Comment by danparsonson | Hacker News Reader

https://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exc...

If Meta are turning it off then I guess it's reasonable to assume that there is something to turn off.

Diffe-Hellman-Merkel key exchange is vulnerable to attacker-in-the-middle attacks.

Eave could just do key negotiation with Alice and separately do key negotiation with Bob. You have to use a slightly more complicated cryptographic protocol to avoid this issue.

The only way to avoid this issue is if Alice and Bob can talk out-of-band. There's no protocol that fixes this.

True but the out of band secure channel could just be something like DNS, automated and constantly subject to distributed monitoring for deltas.

How would the keys get stored in the user's private browsing window? Do they lose all chat history when they log in on a private browsing window and then close it?

I don't know the technical details of that for sure, but I think the answer is that keys and chat history are stored on-device only; for example you lose your WhatsApp history if you don't restore a backup when moving to a new phone.

If a messaging app is showing you message history in a private browsing window then perhaps the encryption key for that history is derived from your password or something like that; that can be done locally so that all the server ever sees is encrypted data.

If you log in to the app on one phone and then in a web browser should you still be able to see your messages in the web browser?

Sorry do you mean, that's how it works now, or, that's how you think it should work? Are you talking about Instagram or WA or something else?

edit: misread your message; if you have two sessions active at the same time, then yes I would expect both sessions to receive the same messages.

What if you log into the app and then log out of the app and then log into the app again? Should you be able to see your messages?

E2EE is a fail-secure design. In case of any doubt it deletes your private messages. When applied to this case I don't think the downside of constantly losing all your messages outweighs the upside of Facebook pretending they don't have a copy of all of them.

Are you asking for technical details about E2EE in messaging apps, or simply making the point that you don't like it? If you don't like it, then fine, you do you, however I would point out that we all accept some inconvenience in our lives as a trade off for improved security; the lock on my front door is inconvenient but I'd rather have it than not.

As to whether or not Meta have been lying about it, then that would be on-brand for them, but then what are they turning off if so? Or maybe the whole thing is theatre, and I should better disconnect from the internet altogether? I don't see the value in speculating about that.

I'm asking you about how you want the world to work.

Well then, I think E2EE is a good thing and I'll take the minor inconveniences.

Not being able to receive messages except on one device isn't a minor inconvenience.

To fix this, you either need to authorize each device (and web browser) from another device that's logged in, or the central authority holds your keys.

I run WhatsApp concurrently on two phones and receive all messages on both devices. But generally speaking this is where we disagree - requiring all devices to be authorised by me is feature not a bug as far as I'm concerned.

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