I think you’ve got it but just to clarify, we do take advantage of the Web’s PKI and DNS for the Interledger application layer protocol SPSP and for some bilateral communication.
When you use SPSP, the payer fetches the payee’s details from a given HTTPS endpoint. These details include an ILP address and shared secret. The secret is used to ensure that the packets sent can only be fulfilled by the correct receiver. If packets are misrouted, they will all be rejected because that other receiver does not have the shared secret to generate the fulfillments.
With ILP-Over-HTTP, peers use HTTPS to send packets to one another. This leverages DNS and TLS to make configuration easier (than if we needed to hard code static IP addresses) and secure the connection.
For more information about Interledger routing, take a look at: