Making RFIDs unique - radio frequency certificates of authenticity

A certificate of authenticity (COA) is an inexpensive, digitally signed physical object that has a random unique structure with high cost of near-exact reproduction. An additional requirement is that the uniqueness of COA´s random structure can be verified using an inexpensive device. We propose a design for objects that behave as COAs in the electromagnetic (EM) field. The objective is to complement RFIDs so that they are physically, not only digitally, unique and hard to replicate. By enabling this feature, we hope to create a super-tag whose data about the product can be read in the far-field, and also whose authenticity can be verified off-line within its near-field with low probability of a false alarm. Thus, radio frequency (RF) COAs are built based upon near-field effects exhibited when RF waves interact with complex, random, and dense objects. In general, an object created as a random constellation of small (diameter > 1 mm) randomly-shaped conductive and/or dielectric objects should have distinct behavior in its near-field when exposed to RF waves coming from a specific point and with frequencies across the RF spectrum. Issuing and verifying COAs is done using standard public-key cryptography. A peculiar feature of our system, not present in previous proposals, is the difficulty of creating a COA instance that produces a given response