Metasurface‐Assisted Indirect‐Observation Cryptographic System

Abstract Metasurfaces provide a novel platform for information encryption due to their incomparable competence for the manipulation of different optical characteristics. Most current encryption schemes, however, decrypt the hidden information through a direct illumination of the metasurface, and the security of which cannot be fully guaranteed since the number of illumination condition is very limited and vulnerable for exhaustive attack. Herein, a cryptographic system based on the indirect‐observation decryption is proposed, the hidden information of which can only be decoded by combining the metasurface‐transformed ciphertext and particular decryption devices based on the digit‐shift images and spatial light modulator, thus possessing ultra‐high confidentiality. In addition, an anti‐counterfeiting label is designed to guarantee the information authenticity. This work builds a distinct bridge between metasurface and other light‐manipulation elements, nanoprint and hologram, and amplitude‐ and phase‐modulated information, thus opening up a new methodology for constructing cryptographic systems in an indirect‐observation way, which may promote the advanced exploration of optical multiplexing and steganography.