Both advances in nanoscale fabrication and in-depth understanding to physical mechanisms tailoring radiative properties paved the way for a cryptographic system utilizing periodic nanostructures and their optical responses. Here we numerically demonstrated working principles and capabilities of the system with a representative nanostructure and its specular reflectance. The ciphertext was a binary surface-relief silver grating and a series of numbers, which contained the information of the sender’s signature and plaintext. Though principles were universal to everyone using the system, messages kept their security because keys could much vary among each communication and different keys were employed for encryption/decryption. The system thus guaranteed the confidentiality and authentication of a message while high-density information could be hidden and delivered with a tiny or even a virtual structure. This work also presented strategies enhancing the safety of the proposed cryptographic system.

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