yes, I had in mind inventing my own secure transmission thingy but it started to get a bit sticky - using a unique identifier on the linux box as you suggest. Like you say a bit of a pain. It seems the consensus is that ssh is the way to go then and arp and MAC addresses isn't - even if my data is encrypted I don't want it poked at by just anyone. Thanks everyone. 2 mins of monkly advice is worth 2 weeks of my arsing about.