Asymmetric multi-image encoding and hiding scheme with structured fingerprint phase masks using gyrator transform and phase-shifting digital holography

We propose a novel technique for multi-image encryption and hiding scheme under optical asymmetric frame work using structured fingerprint phase masks in the gyrator transform domain and three-step phase-shifting digital holography. A structured fingerprint phase mask contains the unique features of fingerprint and structured phase of optical vortex beam, which provides higher security in the cryptosystem. In order to perform the encryption of multiple images, gyrator transform based phase truncation and phase reservation technique has been used in the first level of security whereas three step phase-shifting digital holography has been used to obtain the final ciphertext. This ciphertext is embedded in the host image to perform the watermarking process. In this process, the host is further decomposed into three parts in which anyone from the last two parts can be used for watermark embedding whereas first part is stored as key. The use of polar decomposition in the watermarking process provides additional layer for security. Numerical simulation and experimental results have been presented to support the proposed scheme.