Correlation operation in the Fresnel domain and truncation operations applied to the simultaneous encryption of two images

A new nonlinear encryption-decryption scheme for two images using: double random phase encoding (DRPE), random phase masks (RPMs), amplitude and phase encoding, correlation operation in Fresnel domain (FrD) and truncation operations (amplitude truncation, AT and phase truncation, PT), is proposed. AT and PT are operations that work on complex-valued functions (images) in a nonlinear way, with the purpose of selecting the information contained in a complex-valued image, respectively. The first step of the encryption scheme is encoding two original images in amplitude and phase. The encryption or decryption scheme utilizes the correlation operation in FrD, AT, PT and two RPMs in a specific way to obtain the encrypted or decrypted images. The use of the AT and PT operations allow a better security of the encryption and decryption schemes because the nonlinearities introduced by these operations and the generation of two new encryption keys. The encrypted image of this proposal is real valued and the correlation operation in FrD introduces two new keys improving the security of the encryption and decryption schemes. The keys of the proposed security schemes are six and the right values of these all keys have to be used in the decryption scheme to recover the two initial images used in the input of the encryption scheme.