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This paper proposes a Hash based authentication scheme that employs equal modulus decomposition (EMD) and fractional joint transform correlator. An 8-bit grey scale image is separated into its constituent bit plane matrices. Each bit plane matrix is subjected to EMD encryption procedure employing numerically generated random phase mask (RPM) and amplitude mask (AM). The EMD encryption results into two complex functions, which are used for the generation of phase mask and amplitude mask for the next bit plane matrix. A two round EMD procedure is carried out to obtain an 8-bit intensity matrix which is Fourier transformed and its central frequency components are extracted to obtain a 256-bit Hash value. Numerical simulations have been carried out to validate the effectiveness and performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we show that amplitude- and phase-truncation-based optical asymmetric cryptosystem is vulnerable to known-plaintext attack. The decryption keys are generated with the help of modified Gerchberg–Saxton phase retrieval algorithm from known-plaintext and ciphertext. With the help of the generated keys, the encrypted image, which is encrypted using encryption keys placed in either of the domains (Fourier, Fresnel, or fractional Fourier domain) is decrypted successfully. The vulnerability is proved through the results of computer simulation. [Copyright &y& Elsevier]

Abstract: A novel double image encryption method is proposed by utilizing double pixel scrambling technique and random fractional Fourier domain encoding. One of the two original images is encoded into the phase of a complex signal after being scrambled by one matrix, and the other original image encoded into its amplitude after being scrambled by another matrix. The complex signal is then encrypted into stationary white noise by utilizing double random phase encoding in fractional Fourier domain. By applying the correct keys with fractional orders, the random phase masks and the pixel scrambling operation, the two original images can be retrieved without cross-talk. Numerical simulations have been done to prove the validity and the security of the proposed encryption method. [Copyright &y& Elsevier]