According to Wikipedia Near Field Communication is intended for short-distance communication – something like less than a meter. I wonder how could this limitation be enforced?
Usually there're these factors that limit radio communication range:
- radio waves being absorbed and/or diffused by obstacles
- other radiation being present
- initial signal strength
- receiver sensitivity
At short distances the latter two factors are the key. Usually specifications will regulate the maximum transmitter power and expected receiver sensitivity and this effectively sets up the communication range.
Now suppose I want to create some fraudulent device that would communicate with devices without owners' consent. The specification will say the transmitter must have no more than some power, but I could easily make it times more powerful. The specification will say some level of sensitivity is required, but I could make a more sensitive receiver. I suppose with such adjustments I could make a device that would communicate with ordinary devices over several meters distance and no layman would notice that.
How does NFC protect from such abuse leading to unwanted communication over distance longer than expected? How could maximum communication distance of less than a meter be enforced?
Best Answer
Do you intend to sell this device? If so, prevention is guaranteed by the fact that you'll never get FCC approval for it.
If you're approaching it from a security standpoint, imagining a target which is relying on NFC restrictions of 1 meter vs. several meters to protect valuable data, you could create such a device. It would be expensive, and thoroughly illegal. If your target has data that's worth more than the cost to build such a device, then they're probably not going to keep it in a format where it could be accessed via NFC.