Block the blocker: A blocker-tag agnostic ALOHA-based tag reading protocol in dense RFID system

Blocker tags are special-tags conceived to protect the customers privacy from unauthorized readers that viciously attempt to read the RFID tagged products carried by them. Unlike normal RFID tags, the blocker tag participates repeatedly in a tag-reading process and generates fake tag-IDentifiers (IDs). In all other respects it behaves well like a normal tag so that a reader invariably treats each fake ID as if it were a true ID from an actual tag. In other words, the blocker tag emulates multiple tags in the system. The reader's output is therefore obscured with an indistinguishable mix of fake-IDs and actual tag IDs. In an ALOHA-based tag reading system, a blocker tag probabilistically participates in the MAC protocol arbitrated by the reader. The higher the probability more contaminated the reader's result (with fake-IDs), and higher degree of protection from privacy snooping. Despite the salient use of the blocker tags, they can also be used maliciously to perform a Denial-of-Service attack on a trusted reader. As a result, the reader indefinitely interrogates the tags, and also incapable of isolating the actual tags in the system. While existing works detect and/or identify blocker tags in the system; to the best of our knowledge, there is no automated solution proposed to enable an authorized industry-compatible ALOHA-based RFID reader to perform a time-bounded effective tag-reading in the presence of a malicious blocker tag. In this paper, we present a simple yet novel solution to detect and jam the blocker tag from interrupting an on-going ALOHA-based tag-reading process. Through mathematical investigation and subsequent validation by simulation, we demonstrate the effectiveness of our solution.