RFID identifies a physical object using its unique ID recorded
in the RFID tag. On the other hand, in many business processes
such as incoming shipment inspection, not only identity of individual
objects but also the integrity of a group of objects needs
to be verified. Fig. 1 shows an example usage scenario for group
verification in an RFID portal. A group of RFID tagged objects
on a pallet passes through the portal. If the integrity of the group
is verified, we can just let the pallet go. When the integrity is not
verified, we stop the pallet and redo the scan to confirm that objects
have gone missing during transportation and handling. We
may search for missing objects after consulting the shipment
list. Automatic verification of the integrity and the determination
of number of missing objects can reduce the time and cost
of such process. The determinated number of missing objects
provides the useful information to locate missing objects.
In existing RFID systems, such group verification is done by
looking up the list of grouped objects, such as the Advanced
Shipment Notification (ASN), after individual identification.
This type of verification usually requires a network connection
to retrieve the list of grouped objects. However, verification of
the integrity of a group is required not only in a network-reachable
environment but also in an offline environment. This
motivated us to establish a method to verify the integrity of a
group of objects without a network connection.
Group verification of RFID tagged objects has been studied
from the perspective of security. Juels [1] introduced a yoking
proof by chaining the message authentication code (MAC) with
an external verifier. Other researches ([2]–[6]) essentially improve
the yoking proof or generalize the yoking proof to a group
of multiple RFID tags. Inoue [7] introduced a systematic scheme
which detects failure to read of RFID tags based on a statistical
analysis of reading results from multiple readers. Potdar
[8] proposed an integrity-check method which uses total weight
of grouped objects and reading result of RFID tags. All of these
approaches require an external verifier or database.