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What has a point x=9, and protects your security?

Well, that will be Curve 25519, and takes a base point at x=9, and then uses:

and where p = 2²⁵⁵-19. It is a curve that is used in lots of applications, including within the Tor network, and where each Tor node performs a Curve 25519 ECDH key exchange (known as X25519). Each of nodes then end up with their own derived symmetric key, and the encryption is performed with onion…