The use of Physical unclonable function (PUF) is becoming more popular to enhance information security through advanced cryptographic keys that cannot be replicated. PUF keys using non-replicable serial numbers provide a stronger level of encryption as the amount of data increases. 

However, the cryptographic keys of the conventional PUFs are not reconfigurable from the ones assigned at the manufacturing stage and the overall authentication process slows down as the number of entities in the dataset or the length of the cryptographic key increases. 

To resolve the disadvantages of PUFs, we present a new supersaturated solution-based PUF (S-PUF) that allows a time-efficient, hierarchical authentication process together with the rewritability of encryption keys. S-PUF generates encryption keys of a random speckle pattern caused by interference as the laser beam passes through randomly generated sodium acetate crystal grains. 

S-PUF can determine the orientation and average grain size of sodium acetate crystal while maintaining the random characteristics of crystallization via a spatiotemporally programmed temperature profile. This allows S-PUF to selectively specify the diffraction direction of light and the degree of divergence as two new global variables, i.e., the rotation angle and divergence angle. 

In addition to non-replicable speckle patterns, the divergence angle and the rotation angle are introduced as prefixes to classify stored data, enabling more efficient analysis of encoded information from a vast array of speckle patterns. 

Furthermore, the reversible phase change of sodium acetate in S-PUF substantiate the huge potential for multiple use of cryptographic key, which is anticipated to provide innovative opportunities for a new, sustainable anti-counterfeiting platform in the future.

A schematic diagram of the operation principle of saturated solution-based S-PUF and the authentication system of S-PUF.

[Reference] Y. Kim. et al., Reconfigurable Multilevel Optical PUF by Spatiotemporally Programmed Crystallization of Supersaturated Solution, Advanced Materials, 2023. 10.1002/adma.202212294.

[Main Author] Youngchan Kim(Hanyang university), Sukjoon Hong(Hanyang university, ERICA)

* Contact : Professor Sukjoon Hong (sukjoonhong@hanyang.ac.kr)