Rethinking Tag Collisions for Replay and Relay Attack Resistance in Backscatter Networks

Distinguishable physical layer features of radio frequency have the potential to serve as new fingerprints for authentication in backscatter networks. They have a definite advantage that backscatter tags do not have to run resource-intensive operations that commodity tags rarely implement. However, current physical layer authentication schemes impose substantial burdens on both service providers and users. Since physical layer features are highly susceptible to environmental factors, labor-intensive and time-consuming fingerprint library establishment is indispensable to make sufficient statistics for authentication. In this paper, we propose TagDuet, a collision-assisted authentication scheme that adopts an auxiliary tag to RFID systems, a typical type of backscatter networks, without the requirement of fingerprint library establishment. TagDuet places an independent backscatter tag in the proximity of a reader and utilizes the features in intended tag collisions to improve wireless security. Our phase cancellation decoding algorithm accurately decodes the collisions, which leads TagDuet fully compatible with the commodity RFID tags. TagDuet provides freshness, the paramount property to resist replay attacks, and robustness to relay attacks under FCC regulations for frequency hopping. We implement a prototype of TagDuet with commodity tags, evaluate the performance in randomized channels by the auxiliary tag, and demonstrate the resilience against replay and relay attacks.