Spatial-identification image encryption based on digital holography

Abstract

We present a new method of realizing the spatial-identification image encryption based on digital holography in order to improve the encryption degree and increase encryption freedom. Both the object beam and the reference beam are modulated with random phase respectively. The random phase displayed on the spatial light modulator (SLM) in the reference arm is being refreshed synchronously when the aperture is scanning over the original image. The original image is divided into many subareas by the scanning aperture, and the object beam from each subarea interferes with a reference beam with unique random phase. Therefore, many sub-holograms are captured and each sub-hologram is encrypted with its own sub-key. The spatial position of the aperture becomes additional secret key because it is necessary that each sub-key should match with each encrypted sub-hologram for obtaining a completely decrypted image. This method greatly improves the image encryption degree and guarantees the security of the information. The whole original image is retrieved by superposition of all decrypted subareas. The encryption and decryption are demonstrated by simulations.