Near Field Communication (NFC) is a contact-less communication technology based on a radio frequency (RF) field using a base frequency of 13.56 MHz. NFC technology is perfectly designed to exchange data between two devices through a simple touch gesture.
The RF field generated by an NFC Forum Device to communicate with an NFC Forum Tag has three tasks:
- To transfer power from the NFC Forum Device to the NFC Forum Tag. Therefore the NFC Forum Tags don’t need batteries or other power supplies for operation as the necessary power for communication is provided by the RF field. This technology is also ideal for small IoT devices acting as an NFC Forum Tag as no additional power is needed for the NFC communication.
For Wireless Charging the primary goal of NFC Technology is to transfer power thus extending communication. In this case NFC communication is used to regulate the power transfer. When Wireless Charging mode is active the field strength of the RF field can be increased allowing a power transfer of up to 1 W.
- The NFC device is sending information to an NFC Forum Tag by modulating the RF field signal (signal modulation).
- The NFC device is receiving information from an NFC Forum Tag by sensing the modulation of the load generated by the NFC Forum tag (load modulation).
NFC technology is designed for an operation distance of a few centimeters, this makes it more difficult for attackers to record the communication between an NFC Forum Device and an NFC Forum Tag compared to other wireless technologies which have a working distance of several meters. In addition, the user of the NFC Forum Device determines by the touch gesture which entity the NFC communication should take place, which makes it more difficult for the attacker to get connected. As a result, the security level of the NFC communication is by default higher compared to other wireless communication protocols. Additionally, the NFC Forum has added Peer to Peer communication which is a mechanism to cipher all exchanged data to avoid that a spy can interpret recorded communication.
NFC and other Contactless Protocols
NFC communication technology is used by several different existing contact-less communication protocols in the market which use different coding for signal and load modulation. The NFC Forum created a set of specifications allowing NFC Forum Devices to use these different communication protocols. As a result, NFC Forum Devices are able to communicate with:
- Readers and cards compliant to the ISO/IEC 14443 Type A standard
- Readers and cards compliant to the ISO/IEC 14443 Type B standard
- Cards compliant to the ISO/IEC 15693 standard
- Devices compliant to the ISO/IEC 18092 standard
- Readers and cards compliant to the JIS-X 6319-4 standard
- NFC Forum Tags
- Other NFC Forum Devices
Depending on the communication protocol used and the capability of the remote device, a communication speed of up to 424 Kbit/s is supported by NFC Forum Devices.
Schematics of NFC Forum Devices
The principal schematics of a typical NFC Forum Device can be described by the following diagram:
The NFC Controller connected with an antenna transmits and receives all NFC communication frames of the NFC Forum Device. NFC applications which are initiating and managing the NFC transactions are either:
- apps located in the Device Host using the NFC API of the operating system inside the NFC Forum Device or are
- located inside an optional available secure element directly connected to the NFC Controller.
To support the implementation of interoperable NFC Forum Devices, the NFC Forum has defined the NFC Controller Interface (NCI) between an NFC Controller and the Device Host of the NFC Forum Device.
Operation modes of NFC Forum Devices
Depending of the actual use case the NFC Forum Device can operate in four different operation modes
Reader / Writer mode
The NFC Forum Device operates like a contact-less reader device which is able to communicate with contact-less tags or cards. A typical use case is to read smart posters, opening a specific internet web site for example.
Two NFC Forum Devices are touched together to exchange data. This mode is used to easily exchange the contact data of the device users for example.
Card Emulation mode
The NFC Forum Device operates like a contact-less card that is able to communicate with a contact-less reader device. Typical use cases are the emulation of contact-less banking cards to perform money transactions or to emulate contact-less tickets for public transport.
Host Card Emulation
With this implementation, an HCE app located in the Device Host is taking care of emulating the contact-less card. In this configuration, the NFC Controller is forwarding all received contact-less commands to the Device Host. The HCE app can then communicate with the contactless reader device by using the NFC API.
Wireless Charging mode
This mode is used to transfer power. Communication is performed to manage the power transfer. The NFC Wireless Charging mode allows the contact-less transfer of up to 1 W power. This mode will charge small IoT devices with a limited power supply such as a Bluetooth headset, fitness tracker or smartwatch. NFC Forum Devices capable of the Wireless Charging mode have the ability to charge these kinds of IoT Devices.
Alternatively, these IoT Devices can be also charged by dedicated NFC Wireless Chargers
Secure Element based Card Emulation
With this mode, the emulation of the contact-less card is managed by a secure element inside the NFC Forum Device. This Secure Element can be either a security chip embedded in the NFC Forum Device or an NFC enabled SIM card inserted in the NFC Forum Device. For both solutions, the commands received from the contactless reader will be forwarded to the secure element for processing. This implementation allows the same high-security level for transactions as those provided by contact-less smart card solutions.
These operating modes are available at the same time as the NFC Forum Device generates periodically for a short time frame an RF field to sense for a remote device. The NFC Forum Device will initiate a Reader/Writer, Peer-to-Peer or Wireless Charging operation mode in the event a remote device is detected. The rest of the time the NFC Forum Device listens for communication requests from remote contact-less reader devices or NFC Forum Devices and answers to their communication requests.
As the time period for generating an RF field is significantly shorter than the listen time period the reception of NFC communication requires only a relatively low power supply. The user will normally not identify a significant reduction in the battery run time on his/her mobile NFC Forum Device when enabling the NFC function all the time.
NFC Forum Tags
NFC Forum Tags are contact-less memory cards hosting a so called NDEF message (NDEF is standing for NFC Data Exchange Format) defined by an NFC Forum Specification. NFC Forum has currently defined five different NFC Forum Tag types to allow the usage of many different existing memory card implementations as NFC Forum Tags. These different NFC Forum Tag types differ by the underlying communication protocol and data structure to store NDEF messages but the resulting overall behavior of NFC Forum Tags is identical.
An NFC Forum Device reading the NDEF message from an NFC Forum Tag will initiate a specific action according to the information stored in this NDEF message. As lots of information can be stored in an NFC Forum Tag, there are many different actions triggered when read by the NFC Forum Device. The following table shows some of the common used data types and the typical corresponding actions initiated by the NFC Forum Device:
|Information stored on NFC Forum Tag||Action initiated at NFC Forum Device|
|Internet link (URL)||Show the linked web site|
|Phone number||Initiate a phone call|
|Short message||Send a short message|
|Send an e-mail|
|Point of interest||Shows a map with the point of interest|
|Address||Start navigation to this address|
|Contact data||Store the contact data on the NFC Forum Device|
|Bluetooth pairing information||Pair with the Bluetooth device|
|WiFi keys||Login at the WLAN router|
Depending of the actual context, the NFC Forum Device may also trigger alternative actions. For example, if the NFC Forum Device identifies that it is already connected with the Bluetooth Device when reading an NFC Forum Tag with Bluetooth pairing information, then the NFC Forum Device may disconnect the connection with this Bluetooth device.
For security sensitive actions, the NFC Forum has also defined a mechanism to add a signature to the NDEF Message allowing the user to verify if the NDEF message was generated by a trustworthy source.
Apps installed on NFC Forum Devices can extend or modify the behavior when the NFC Forum Device reads NFC Forum Tags. This allows for many additional data types which can be stored on NFC Forum Tags to trigger different actions on the NFC Forum Device. To support such applications, the NFC Forum specification also provides the definition of proprietary data formats which are identified by the internet domain namespace from the application provider.
Comparison with other wireless technologies
There are different wireless technologies on the market which are replacing a cable-based connection. These technologies allow a data transfer with a range of up to 100 meters. It is common for these technologies that receiver devices need their own power supply due to the larger working distance, thus the receiving device cannot be powered by the RF field. Another consequence of the larger working distance is the need for the user to configure their device and to pair them together for the communication as this connection cannot be initiated by a simple touch gesture. For these wireless technologies NFC provides an additional service as it can simplify the pairing process between two devices. Famous examples for these wireless technologies are Bluetooth, Wi-Fi and Zigbee technology.
The IrDa technology is a short range (a few meters) connection based on the exchange of data over infrared light. To make an IrDA connection the user must position the two communication devices within a line of sight. For larger data communication with computer devices this technology was replaced by Bluetooth or WiFi connections, this is why IrDa technology today is mainly used for remote control devices. Similar to the previously described wireless technologies, the IrDA receiver must also have its own power supply.
RFID technologies uses a similar communication technology as NFC technology but it uses other base frequencies for the generated RF field. These technologies are used in various markets however they do not target the wide range of use cases as NFC offers for consumers and end customers.