Near Field Communication Primer

Posted by antitree on Wed 21 December 2011

image0I thought I'd do a primer about NFC since Samsung's Galaxy Nexus is getting a lot of press about it. You may have heard of Google Wallet or how NFC is going to be built into smart phones in the future. Maybe you haven't thought about how it works or how to hack it. As a side[side(side)] project I've been working on NFC research with (as always for me) a specific focus on the security perspectives. This is an overview of NFC to maybe peak your interest.


Near Field Communication is a way to transmit information between intelligent devices. I know you're already thinking Bluetooth but wait. NFC has a limitation that says in its spec that it can't be more than .2m away from its partner during communication. It may be a bit more depending on the implementation but the thing to remember here is that the protocol itself is what limits the distance, not just the hardware. (Quit pointing that gigantic antenna at my pocket right now!) It transmits on the HF band 13.56MHz, a frequency already used by some RFID chips and fun devices like the Proxmark 3.


Here's what's different about NFC: There are three different modes.

  • Reader/Writer: Commonly used in smart posters or smart stickers. Think QR code but subtle.
  • Peer to Peer: Data is exchanged back and forth between devices; securely exchange credit cards, give your friend your home WIFI settings, or exchange business cards.
  • Card Emulation: A device acts like a contactless smart card. What if you could use your phone as a bus pass instead of keeping that flimsy magstripe pass in your pocket?


Lets take care of that up front. NFC sounds a lot like RFID (they share the whole RF thing) and it seems to get stored in people's heads that way because NFC has the card emulation mode where it emulates at "tag" or an RFID chip.  RFID isn't usually much more than a tag blindly broadcasting data hoping a receiver picks it up. Passive tags (or little antennas without a power source) sit and wait for an RFID reader to come by to energize them. They get all excited and tell the reader everything they know. Imagine a dog just waiting at the door for it's owner to come home. The active RFID tags have a battery in them that constantly broadcasts itself to anyone that will listen. Kind of like that annoying friend you have that tells you everything about their life even though you never asked. NFC on the other hand is like an intelligent college student. She can have an intimate conversation with you, she can make a presentation in front of a class, but she can still get drunk and act stupid if that's what everyone else is doing at the party.

NFC is not a new technology

We've seen them in European phones since 2003 or 4 and they've been hacked on for just as long. The folks at the Chaos Computer Club have been hacking on NFC since it's original inception; when manufacturers like Nokia started installing it into their feature phones, AKA dumb phones. It never made it across the water - some may say due to some FCC regulations on the 13.56 frequency but I'll leave that topic to the Ham guys.


If you haven't already, you should put on your tin foil hat now. NFC is a way for corporations to take over our bodies, man! Well...most likely not. But you're already thinking about the security problems as soon as I wrote "credit card." I'm going to save this whole discussion for another day but the tl;dr version is that NFC has been designed with security in mind but a lot is left up to the developer to implement securely. We all know how well that works especially for mobile app developers so I'm sure everything is going to be fine, right? Maybe next time I'll tell you about the butt sniffing attack. No seriously.

Android and The Galaxy Nexus

How is Android implementing NFC in the Galaxy Nexus? Here's an example of a peer to peer mode connection: When you put a Galaxy Nexus next to another Galaxy Nexus, the phone will make an NFC connection as long as both phones are unlocked. If the app that you  have open supports NFC (i.e. Google Maps) it will allow you to communicate data from your app to the other device. Some examples of this are sharing contact information, location data, websites, etc but apparently it's going to be used for games or whatever developers can think of.

The Reader/Writer mode will allow you to take an NFC tag and shove it next to the phone. Depending on the data stored on the card, it will open an appropriate app to view the content. In the case of an NFC tag that is contains a URL, it will automatically go to that page. Ask me about some of the NFC tags I've made at a 2600 meeting sometime. :)

More info:

If you want to see a much better post that's chock full of info check this out:

Here' s a random YouTube video of two guys with Galaxy Nexuses so I don't have to make one: