Near field communication (NFC) systems provide a good location-limited channel so that many security systems can use it to force the participants to stay close to each other. Unfortunately, only a small number of smart devices in the market are equipped with NFC chips that are essential for NFC systems. The purpose of this paper is to provide the same feature, called near field authentication (NFA), without using NFC chips. We propose an easy-to-use system to achieve NFA by using human finger movement on the touch screens of two nearby smart devices. Our system does not need any prior secret information shared between two devices and generates the same high-entropy cryptographic key for both devices in a successful authentication. The efficiency of the system is demonstrated by our evaluation on a Motorola Droid smartphone.