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Study Of Optical Information Security Techniques Based On Phase Retrieval Algorithm And Transport Of Intensity Equation

Posted on:2016-12-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:C G ZhangFull Text:PDF
GTID:1108330482951469Subject:Optical Engineering
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With the development of the Internet and mobile communication technology, the human society has been in the era of information. From a personal perspective, the wide use of digital cameras and mobile phones generates plenty of intimate photos and private information, which need to be stored and transmitted carefully; at the organization level, the data in e-business and online banking is always under the threat of the hackers; at the nation level, the confidential data storage and communication in government and military department are big issues which are hotspots in the study of information security. Information security becomes an important issue nowadays. As a new kind of security techniques, the optical information security develops rapidly.Since the image encryption method based on double random phase encoding was invented by Refregier and Javidi in 1995, the optical information security technique has drawn a lot of attention for its large capacity, the inherent capability for parallel processing and multi-dimensional encoding. Numerous scholars devote themselves to this research area and plenty of works have been published.This dissertation focuses on the optical information security, including cryptanalysis, cryptography and information hiding. First, two optical cryptosystems are analyzed and two attack methods are provided. The simulation results show that these systems are insecure. Then a cryptosystem based on phase-truncated Fresnel diffraction and transport of intensity equation is proposed. Though this cryptosystem has a simple optical setup, it is immune to existing attacks. At last, an optical steganography based on phase-encoded Fresnel diffraction and transport of intensity equation is presented. It has a large capacity while keeps the imperceptibility as well. The major contributions of this dissertation are summarized as follows:(1) A ciphertext-only attack(COA) scheme to evaluate the security strength of optical encryption based on the joint transform correlator(JTC) scheme is proposed. This COA strategy converts the COA into a phase retrieval problem with single intensity measurement. Therefore the hybrid input-output(HIO) iterative phase retrieval technique can be used to solve this problem. From the point of view of cryptanalysis it is also reasonable to acquire the parameters of the encryption architecture, which are then used to construct the signal domain support. In such a way, the plaintext can be successfully retrieved with sufficient precision from the corresponding ciphertext. A set of numerical simulation results have demonstrated the feasibility and validity of the proposed method and show that the JTC encryption scheme is vulnerable to the COA scheme.(2) A new attack on the double image encryption method(DIEM) based on the generalized amplitude-phase retrieval(GAPR) method is presented. Compared with the cracked results presented by Deng, our method provides a more clear vision of the plaintext. Furthermore, our analysis shows that the DIEM is, in fact, a cascaded scheme, which consist of a JTC architecture and a phase-truncated Fourier transform(PTFT) scheme. According to this analysis, we present a security discussion on the DIEM, which shows that maybe the security of the optical cascaded cryptosystems is not as secure as expected.(3) An optical cryptosystem based on the phase-truncated Fresnel diffraction(PTFD) and transport of intensity equation(TIE) is proposed. Its decryption process is different from the encryption. A random amplitude mask(RAM) and a random phase mask(RPM) are employed as two secret keys to encrypt the input image into a realvalued noise-like intensity distribution. With the help of two secret keys, the ciphertext could be decrypt with the GAPR and TIE methods. Other than the published PTFTbased encryption methods which have to record the truncated phase as the decryption keys(different from the encryption keys), our method only requires the presence of the two encryption keys in the decryption process, and the decrypt plaintext is nearly lossless. Moreover, the generated ciphertext is an intensity distribution, which is convenient to record and transmit. Owing to the nonlinear operation of phase truncation as well as the decryption strategy, a higher security level could be achieved. A set of computer simulations are carried out to show the feasibility and security of the proposed method.(4) A steganography system based on phase-encoding Fresnel diffraction(PEFD) and TIE is proposed. Different from the published works, which embeded information into the space or frequency domain, we encode three secret images into the phase. After Fresnel diffraction, the resultant amplitudes and the original cover image are assembled into a final stego image. To enhance the security, we also propose an identical position pixel scrambling(IPPS) method to encrypt the images. For extraction, we introduce the TIE method to recover the secret information. The recovered images is lossy, however, the main information is well retrieved. Thanks to the optical technique which enables us to encode information into the other dimensions like phase, a large capacity has been achieved while the imperceptibility is well kepted.
Keywords/Search Tags:Optical information security, Optical cryptography, Optical cryptanalysis, Optical information hiding
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