Optical voice hiding based on chaotic fingerprint phase mask and phase-shifting digital holography

Most of the current optical information hiding methods are designed for protecting grayscale or color images. However, as an important information communication medium, the security of voice has also received a lot of attention in several application areas. In this paper, we propose an optical voice hiding scheme based on chaotic fingerprint phase masks (CFPMs) and three-step phase-shifting digital holography (PSDH). In this proposed scheme, the CFPMs are generated from the fingerprint using the secure hash algorithm (SHA-256) and chaotic Henon map. And to hide the voice into a host image, the voice signal is first converted into a two-dimensional (2D) matrix form (i.e., the "voice map"). Then, the "voice map" is encoded into three noise-like holograms using two CFPMs located in Fresnel transform (FrT) domain and three-step PSDH. Finally, the three noise-like holograms are hidden into a color host image using a fusion method based on discrete wavelet transform (DWT), thus achieving the hiding of the voice signal. The security of this optical voice hiding scheme can be greatly improved because the fingerprint key shared by the sender and authorized receiver is closely linked to the user and does not need to be transmitted over the open network. In addition, the parameters of chaotic Henon map and Fresnel diffraction distances can also provide additional security to the proposed scheme. We have verified the feasibility, security and robustness of the proposed scheme through extensive experiments.