Data encryption labels based on stimuli-responsive color-changing and luminescent molecules show great promise in advanced information encryption and anticounterfeiting fields owing to the easy readout by the naked eye, eliminating the need for additional power supplies and wiring, and low cost. However, the response behavior of these smart materials is simple and predictable, so it is easy for hackers to copy or imitate, leading to information leakage or forgery. 

Sequential logic encryption (SLE) requires the recipient of the terminal information to input the exact preset sequence keys and disallows trial-and-error attacks, bringing it higher secure levels and enabling broad applications in "end-to-end encryption" (E2EE). However, SLE encryption scheme has, so far, only been used in digital circuits and has not yet been implemented on responsive photochromic and luminescent molecules, probably because its required logical response behavior is beyond the reach of most responsive molecules. 

In a study published in Science Advances, the research group led by Prof. HUANG Weiguo from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences, achieved sequence logic data encryption and anticounterfeiting by harnessing molecular isomerization in polymer gels. 

The researchers designed and synthesized a series of multi-responsive Gel-DASAs with controllable photochromic, thermochromic and hydrochromic characteristics by introducing negative photochromic molecules donor-acceptor Stenhouse adducts (DASAs) into polymer gels, and by manipulating the reversibility of response behavior via diamine conformational locking and substrate free-volume engineering.  

They found that compared with the traditional DASAs molecules, Gel-DASAs are controllably responsive to light, heat, and water stimuli, showing unpredictable and diverse responses and tailored reversibility. Therefore, Gel-DASAs can be utilized to program advanced information encryption systems. 

Besides, the researchers implemented an SLE advanced data encryption system based on these smart materials. The system presents a memory function, which requires the preset sequence keys to decrypt the information.

The output of DASA gel–based data-encryption system depends not only on the present input stimulus but also on the sequence of past inputs. Once entering incorrect sequences, the system would generate fake information to deceive hackers. In addition, only one decryption opportunity was provided, and trial-and-error attacks were disallowed, thus the security level of data encryption system was greatly enhanced. 

This study provides a new way for applying stimuli-responsive materials to advanced E2EE system with SLE scheme. 

Schematic diagram of sequence logic encryption based on stimuli-responsive polymer gel(Image by Prof. HUANG’s group) 

Contact: 

Prof. HUANG Weiguo 

Fujian Institute of Research on the Structure of Matter 

Chinese Academy of Sciences 

Email: whuang@fjirsm.ac.cn