LAUSR

DOI: 10.1002/adom.202102402 Union (EU), counterfeit products traded in 2019 alone were valued at USD 134 billion (5.8% of the EU imports).[1] Beyond economic consequences, counterfeiting can also endanger human lives, for example, by producing unsafe or ineffective pharmaceutical products[3] and compromising safety standards.[4] To combat counterfeiting, an approach gaining significant interest is to uniquely identify products with unclonable labels, often referred to as physically-unclonable functions (PUFs). Unclonable labels rely on micron-scale randomness in the manufacturing process to produce a series of unique labels that are highly resistant to forgery.[5] The unique physical characteristics of each unclonable label are characterized after manufacture and converted to digital codes that are stored in a database. These labels are then attached to a product before it enters the supply chain. Along the chain, any actor (e.g., a distributor or consumer) with the appropriate hardware can check the label’s authenticity by sending the results of their test characterization to compare against the information stored in the database. We note here that a plain serial number can also be attached to the unclonable label so that the test characterization image need only be compared against the references for a given label instead of the complete database. This vastly reduces the number of computationally costly test–reference comparisons that need to be made and therefore drastically reduces authentication time.[3b,6] A schematic of the process described above is presented in Figure S1, Supporting Information. At a system level, such unique identifiers also combat forgery. Given the database and authentication requests are centrally managed, and the authentication requests come from trusted parties (the consumer is not motivated to try to attack the system to achieve a false authentication), if a few single labels are cloned this could be identified by excess requests to authenticate the same label from unexpected geographic locations. The few compromised unique labels could then be flagged as inauthentic. Of course, this is a general feature of serial marking, but one that can be used to further reduce the incentive for embarking on the laborious task of attempting to clone a single label of the design introduced below. The seminal work of Pappu et al. in 2002 was a key event in the launch of interest in unclonable anti-counterfeiting labels.[7] Micron-scale randomness during manufacturing can create unique and unclonable anti-counterfeiting labels. The security of such labels typically comes at the expense of complex hardware being required for authentication. This work demonstrates unclonable labels that can be authenticated using simple hardware such as a standard light-emitting diode and smartphone camera. These labels consist of a microlens array laminated to a luminescentmicroparticle-doped polymer film, and thereby present a new method of making microscopic particle distributions visible on the macroscopic scale. The current novel design offers two significant practical advantages: 1) use of an incoherent source; and 2) authentication independent of the detector position. A comparison of 100 test images against 100 different reference images (total of 10,000 comparisons out of which 100 should authenticate and 9900 should not), demonstrates that authentication is robust with an estimated probability of a false positive on the order of 10−15. Finally, a proofof-concept is demonstrated through successful authentication of a label by a single smartphone, simultaneously providing both excitation and detection on the front side of the label.