We needed a protocol that allowed us to tell a server that we are who we say we are, have it work across NAT, use TCP, UDP, or ICMP as the transport mechanism, act as an extra layer of security, and be secure itself. Oh, and do so with a single packet. Sound crazy? It's actually very useful. We've come up with a Single Packet Authorization (SPA). This is a protocol for a remote user to send in a request to a server which I cannot be replayed and which uniquely identifies the user. The proof-of-concept code alone is worthy of a presentation itself, but SPA is so much more. This is not port-knowcking (although SPA can easily replace port-knocking with something much more secure).