You have simply misunderstood me. I'm trying to explain deeply :)
When grub starts, it asks for a choice, lets take this, as an example:
1) Linux
2) Linux (mem test ecc)
3) Windows 7
4) Windows Server 2000
I want grub to listen for an encrypted UDP packet that emulate an human choice.
Continuing the example:
1) send a WOL to aa:bb:cc:dd:ee:ff
2) start an UDP loop to the same mac address, to start the 3rd grub menu' choice (in this example, windows 7)
3) when grub receive that UDP packet, successfully decrypts it and it is sure that this packet is trusted (rsa or what you want), selects that menu choice
4) grub boots the selected item.
No files are passed in any way. I'm telling GRUB to boot a specific and preconfigured entry.
In the UDP packet, I'm thinking to insert a grub command line. This is very similar to pressing E when grub asks what to do at boot.
I'm not sure of why you have wrote about kernel files. I never wrote about sending files because this should be done by a PXE or bootp but this is NOT my goal.
Another very useful thing, should be that GRUB sends an encrypted UDP packet with his menu configuration in order to do a reasonable choice from a third party application.
Many thanks for your time.
Daniele.