Harnessing NFC to Generate Standard Optical Barcodes for NFC-Missing Smartphones

Mobile payments have grown significantly recently, driven by their contactless feature that minimizes COVID-19 transmission risks. While NFC offers more security and convenience than barcodes and benefits those with amblyopia, many smartphones lack NFC due to module shortages or security decisions. In this work, we present ${\sf MagCode}$ , an innovative method connecting NFC readers with cameras, allowing users to enjoy NFC payment security using prevalent camera technology. At the heart of ${\sf MagCode}$ is the harmless magnetic interference on the CMOS image sensor of a smartphone placed nearby the NFC reader, resulting in a group of barcode-like stripes appearing on the captured images. We take advantage of these stripes to encode the data and achieve simplex communication from an NFC reader to an NFC-denied or NFC-disabled smartphone. In particular, we developed a comprehensive suite of protocols spanning from the physical layer to the transport layer, and we rigorously tested our proof-of-concept prototype on 11 different smart devices. Our extensive evaluations showcase a maximum throughput of 2.58 kbps-surpassing magnetometer-based alternatives by a factor of 58-and demonstrate an average data exchange time of 1.3 seconds for mobile payment transactions between an NFC reader and a smartphone.