(headers + body, in Freenet) should be encrypted before giving to PO
Diffie-Helman key exchange, which allows nodes to agree on a symmetric key
over an insecure channel – BUT Man-In-The-Middle attacks are possible by the
PO. So, to do it right, we should negotiate this key using a different PO
(bad – two POs might collaborate), or use a public-private key system.