In an E2EE system, how does Alice know what Bob's public key is?

[ghosttie@mastodon.gamedev.place]

In an E2EE system, how does Alice know what Bob's public key is?

#cryptography

[dacmot@sunny.garden]

@ghosttie it's public, so either Bob can send it to Alice, or if it's part of a system like Signal, then the public key is part (maybe hidden /abstracted) of the user profile data.

[ghosttie@mastodon.gamedev.place]

@dacmot how does Alice know that's Bob's actual public key and not Mallory's?

[dacmot@sunny.garden]

@ghosttie one way would be to meet in person.

In a system like Signal, it would be built in to the user ID. For things like PGP/GPG, websites, or developer signing key, there are multiple mechanisms to verify the key identity. You can use a web of trust (WOT) or keyrings, certificate authorities like DigiCert/Let's Encrypt, or MS/Google/Apple issuing signing keys.

Note that none of those methods are perfect, and a bad actor could still manage to impersonate someone else. But it makes it significantly harder.

[zoarial94@infosec.exchange]

@ghosttie @dacmot I think you need a second communication channel. And something to corroborate that multiple channels are controlled by the same person. The most surefire way is to meet in person and confirm the keys. I don't think there's a purely technical way to solve this without putting trust into some central authority. It's inherently a social problem.