With NFC becoming more popular on phones and NFC circuits requiring no power source, maybe password jewelry could provide positive identification of users? Mak

With NFC becoming more popular on phones and NFC circuits requiring no power source, maybe password jewelry could provide positive identification of users? Make a watch or a ring with a NFC-enabled chip inside, put the required crypto services on it, upload public and private key, and allow devices in range (and websites/apps using those devices as a proxy) to trust it as partial proof of identity by doing the normal challenge-response deal. I guess it'd make a pretty conspicuous target for theft.