I read https://spec.matrix.org/v1.8/client-server-api/#sas-hkdf-calculation https://spec.matrix.org/v1.8/client-server-api/#sas-hkdf-cal... So is it the repres

I read https://spec.matrix.org/v1.8/client-server-api/#sas-hkdf-calculation https://spec.matrix.org/v1.8/client-server-api/#sas-hkdf-cal... So is it the representation in emojis of a server controlled shared secret? That'd make 2 clients talking to eachother through the server vulnerable to tampering at the server level (ex:MITM) Shouldn't the 2 clients not involve the server for the secret? This would require each of them being able to access the other public key fingerprint without trusting what the server says. But if they see eachother fingerprint projected into the unicode emoji space, they would see different emojis. I think I may be missing something obvious. I just don't understand this trick.