Security in printed matter is roughly divided into "property protection" and "individual protection." Banknotes and securities are typical examples of objects that protect property whereas passports and various types of certificates protect individuals. It is no exaggeration to say that society will not function if security in these "valuable things" does not perform correctly. Therefore, we deciphered the type of historical changes that security in printed matter has undergone and how it has been endorsed by people until now. Based on this, the ideal form of universal security required in the future is considered.

Damage caused by counterfeit goods continues to increase worldwide. Companies must implement conscious organizational, legal, and technical measures to prevent counterfeiting. Technical measures are important to ensure that consumers feel secure about their purchases. Various methods of technical measurements according to the characteristics of the product exist; these methods are systematically classified, and the functions and effectiveness of each method are compared. Furthermore, it has become easier to introduce tracking and tracing of goods in recent years owing to the development of digitalization and activities of international organizations, specifically in Europe, which are ahead of the curve. The current state of standards will be described.

This study aimed to examine physical unclonable functions (PUFs) utilizing flexible organic circuits for security in the IoT society. PUFs use inherent manufacturing variations in devices for chip authentication. Therefore, unlike conventional memory data-based security, they can protect against replication and counterfeiting. It is essential to maintain the manufacturing variation in PUFs that serves as the core of the security information and reduces the ID generation error rate. To reduce the error rate, it is useful to suppress the element degradation that causes measurement variations and apply appropriate corrections based on the operational model. Certain characteristics, such as the reproducibility (intra-HD) and uniqueness of IDs (inter-HD), significantly affect the error rate authenticity determination; therefore, it is important to properly estimate them. Since PUFs can utilize various types of variations, preparing separate security elements becomes redundant. For example, by acquiring current variations in the TFT array of a flexible display, it is possible to use them as the source of an encryption key through software or hardware calculations. Therefore, the cost of element implementation can be relatively low in devices, such as flexible displays/sensors, that employ several elements. These devices are expected to play a critical role in IoT security in the future.

Recently, counterfeiting has increased due to improvements in color copier performance. Therefore, highly effective anti-counterfeiting measures and secure authentication technology are essential. In this study, we demonstrate a new printing method for security media using high-definition color printing technology on a thin flexible substrate.

Photo induced reactions by the excitation of plasmon absorption of metal nanoparticles (MNps) have been studied and applied in fabrication of metal patterning. However, the reaction by the irradiation of Nd-YAG pulsed lasers at 1064 nm, at which MNps do not have plasmon absorption, is not well known. Therefore, we prepared typical thiol-stabilized MNps, dodecanethiol or toluenethiol derivatized gold, silver and copper nanoparticles, and formed MNp films on a plate for the observation of photo-induced reactions. Pulsed 1064-nm laser irradiation induced the fusion of the metal particles in the layer with color changes. The fusion phenomena were observed and analyzed by absorption spectra, electron microscopes, thermal analyses and X-ray photoelectron spectroscopy. The size-growth of metal nanoparticles is thought to be initiated by the photothermal conversion, following elimination of thiols protecting the metal particle surfaces. Photo-patterning of MNps were demonstrated with a developing process removing the non-exposure area.