Experimental encryption multiplexing based on a JTC scheme

Abstract

Abstract-We present an alternative scheme to perform a multiple encrypting technique based on the use of a Joint Transform Correlator architecture. The basic approach relies on using an extra random phase mask placed before the correlator input plane, where we select different disjoint regions to encode each input object. In this way we avoid the cross talking when reconstructing the encoded objects. We experimentally validated the procedure using a photorefractive crystal as a storing medium.Encryption techniques are of great importance for data protection [1,2]. In particular, the development of optical encryption attracted increasing interest for its high processing speed and high security level. Conventional optical image-encryption methods are based on the 4-f correlator architecture that uses two random phase masks [1]. This scheme is known as Double Random Phase Encryption (DRPE). An experimental version of this setup was implemented by using photorefractive crystals as storing media. During the decryption procedure, the phase-conjugated beams of the encrypted data allow to obtain the input image [3][4][5]. Several variations of the (DRPE) were proposed in the literature, for instance working in the fractional Fourier domain [6] and by using digital holography [7], to name a few. Encryption techniques imply that the input image should not be recovered without employing the correct encoding key. It should be pointed out that the key code should not be inferred by hackers or unauthorized users. However, it was shown that encryption schemes present some weaknesses. In DRPE hackers demonstrated that they can access random phase keys in both the input plane and the Fourier plane. Chosen and known plaintext attacks [8,9] were employed to efficiently obtain the encoding keys of the system. The mentioned 4f scheme involves the generation of a phase conjugated beam to recover the input image. This holographic scheme requires precise alignment to be experimentally implemented. An alternative encryption technique based on JTC architecture (see Ref.[10]) introduces, in the input plane, both the object to be * E-mail: myrianc@ciop.unlp.edu.ar codified and the key code mask. In the decryption step, after an inverse FT of the joint power spectrum (JPS), which is illuminated by the FT of the exact key code mask, the input image is correctly recovered. This scheme can be also experimentally implemented by using a volume photorefractive intensity-sensitive crystal as storing media. Note that the JTC architecture is an inherent two step holographic set-up, avoiding the use of complex conjugate waves. It was also demonstrated the validity of algorithms for cracking the JTC encryption systems. However, multiplexing turns the system immune to the mentioned attacks, increasing therefore the encryption method security. Multiplexing techniques are based on encoding two or more input images and combining them into a single recording medium. Then, an intruder, who intercepts the encrypted multiplexed data, could not determine by si...