How does a stellar node know that node its communicating with is definitively in or outside its quorum group?

Question

In order for SCP to function properly, a given node has to know that a quorum related message originated from a node in its quorum set.

How does this node know for a fact that the message originated from a quorum-set-included-node, instead of a random node that may be trying to impersonate a node in the quorum set? What if an attacker tried to IP spoof for example?

Answer 1

The protocol consists of exchanging digitally-signed messages bound to nodes' quorum slices.

( https://datatracker.ietf.org/doc/draft-mazieres-dinrg-scp/ )

The trusted nodeIds that you put in your quorum set VALIDATORS configuration are in fact public keys of the secret NODE_SEEDs from the opposing nodes.