E-mail is fundamentally a way to send a sequence of bytes somewhere (untrusted) so they can be picked up later by someone (trusted).
That’s also literally what Signal is built on so I think you’re overstating the difference.
E-mail is store-and-forward just like TCP is; how do you think an IP router works? TCP is fully duplex; a tx doesn’t wait behind an rx, exactly like an e-mail reply not waiting behind an e-mail receive. The only difference is that a router will typically use volatile memory to store messages before they are sent but e-mail will typically use disk.
If your security model relies on this difference then your security model is broken. It’s worth noting that Signal does NOT rely on this difference. It relies on participants being mostly online to permit frequent rekeys and not having to retain old keys indefinitely.
You can't have full forward secrecy with email as it is used today. If you want forward secrecy with email, you need three emails sent in rapid succession: Alice sends a request to Bob, Bob sends a response to accept the request, and Alice sends the actual encrypted email. That would work. But you basically need Bob to be online.
This is partially correct, but they do not need to be in rapid succession, and therefore Bob does not need to be online.
If the messages are slow to come, those ephemeral keys become less and less ephemeral, and could actually be stolen.
> If your security model relies on this difference then your security model is broken. It’s worth noting that Signal does NOT rely on this difference. It relies on participants being mostly online to permit frequent rekeys and not having to retain old keys indefinitely.
Signal does not depend on TCP being "bidirectional" as lvh said, it depends on participants being mostly online. This has nothing to do with the transport properties of e-mail vs. TCP.
Sure. The world of cryptography software is already muddled by misinformation, poor practices and misguided appeals to authority. We shouldn't need to spread misinformation about technologies such as e-mail to get people to stop using it.