Let's start by explaining what RFID tags are. I wouldn't want to post something and have everyone say "That Sunny, he posts so much stuff that nobody understands". An RFID tag is basically like those Security Tags
that stop you from stealing stuff, only it can contain some data as well. There's some more info here
. Basically, you know those eWay tags for the tollways? Imagine those, but smaller, without needing batteries, and fitting into your wallet.
I've been thinking, RFIDs are actually pretty cool, but there's so many shortcomings. One is that they identify you (hence the ID). The other is that anyone can play with the identification (as in, I could see who crosses my front lawn, and/or steal their identification). So it places you at a point, and is still useless for actual identification (unless you use battery powered thingies, but we're talking about the passive tags). There are apparently sleeves which you can put around your tag to stop it from detecting (which fixes the "placing you at a point" problem), but it's still useless for actual identification.
My idea is basically to use it to store your public key. Since it's your public key, it doesn't really mean anything, but it can still be used for identification in a "soft" way. If you need identification (like, say, you want to automatically pay for train tickets without having to buy anything or do anything), then carry an active tag in addition to the passive one, and use normal authentication procedures to verify the private key (note that this wouldn't compromise the private key). In addition, the authentication could go both ways, so the train station would have to authenticate itself with you before you authenticate yourself with the station.
You can put both the passive and active tags on the same device. Since the procedure described above is kinda heavy, maybe have the device as an mmc card or something and make it plug into a palm/pocketpc/etc. This will allow you to Do Cool Things(tm).
So then what can you do with the public key? Well, the public key can be used when initially "introducing" yourself to some entity (such as a train station). In addition, it's set for "preference" things. An example: Say you walk into a Rental Store Of Tomorrow(tm), and it sells DVDs (because it still doesn't offer blu-ray discs, stupid shop), and the DVDs have pretty coloured lights on them. Also, say you're a frequent renter, so you've got their public key in your tag, which will mean you get automatic rental goodness. Now, you're in the shop, and you're just looking around. The DVDs in your proximity that you'll like start glowing green (from previous rental knowledge). The DVDs you've already rented will glow red. It uses your public key to figure this out (it doesn't need to authenticate you, because it's just showing some colours). The worst thing this will allow is for someone to steal your public key and know your DVD preferences.
The DVDs will have RFIDs as well. They'll need batteries (to glow), and the system can tell them which colour (by setting a bit in the active RFID tag in the DVD). So that's my vision of the future: glowing DVDs. w00t!