ABSTRACT
This chapter discusses some of the applications of algorithmic phase retrieval in the field of optical security. There are various iterative phase retrievals algorithms with different rates of convergence and with different requirement of constraints. The chapter describes three major phase retrieval algorithms that have been widely used in optical cryptography. There are: Gerchberg-Saxton algorithm, Error Reduction Algorithm and Hybrid Input-Output Algorithm. Various optical cryptosystems have been proposed in which the decryption or the choice of the random phase masks rely on the method of phase retrieval. Phase functions are obtained in similar fashion for all images. For wavelength multiplexing, different wavelength values for each image are used while implementing the Fresnel transform. As majority of optical cryptosystems are constructed using optical transforms, phase retrieval becomes relevant in these cases to formulate attack algorithms. The chapter shows that the phase retrieval techniques play an important role in the cryptanalysis of optical cryptosystems.
