[geofft]

I'm not sure what to do with systems like iMessage/FaceTime under this definition, where the server doesn't hold the private keys but also the client provides no means to check fingerprints out-of-band. In these systems, the server could MITM the clients to each other and thereby snoop on client communications with the same effective result as Zoom/Jitsi. (These systems also generally support changing the peer's fingerprint without notification.) But we still call those "end-to-end encrypted," right?

Is there a meaningful end-user difference between a design where you have to ask the server for your peer's public key and the server promises to be honest, and a design where the server generates a shared secret and then promises not to use it?

(Note that this question is completely orthogonal to whether the client or server are source-available - unless you can modify the client to display peer fingerprints, merely knowing that you're going to have to trust the server doesn't really change anything.)

[pbhjpbhj]

You appear to also realise that if it's a closed source client then the server could be fine, the client could do all the snooping and pass data in a side channel. It's worth spelling that out IMO.

[wilg]

Even worse, the same could happen if it's an open source client!

[geofft]

Right,

- if it's an open-source client but it doesn't display fingerprints and you haven't modified it, you're stuck. (At least you know you're stuck, but you knew that already.)

- if it's an open-source client but you're trusting someone else's binary, they can attack you.

- if it's an open-source client but you're not trusting someone else's binary, you're not on the embargo list and so responsibly-disclosed bugs are effectively zero-days for you.

- if it's an open-source client but it's written in C, you have no practical way of auditing it against intentionally-malicious source code (i.e., for almost everyone, the cost of auditing it is higher than the cost of visiting your conversation partner in person).

[cpeterso]

How do iMessage and FaceTime provide end-to-end encryption? Is there a public key associated with Apple account? How does my private key get on different Apple devices without my help?

[gruez]

>Is there a public key associated with Apple account

with each device

https://manuals.info.apple.com/MANUALS/1000/MA1902/en_US/app...