Optical Image Encryption Based On Fresnel Transform

Optical encryption technology as a new means of encryption has been developingrecently, the encryption method based on Fresnel transform is one of the most important ofresearch. The research has study several typical image encryption methods for theoreticaland experimental simulation, at the same time combined with traditional decryptionmethod to propose a new method of encryption method.Firstly, this research summarizes the basic principle of the optical image encryptionmethod and introduces the principle of Fourier transform and Fresnel transform, at thesame time analyzed the4f double random phase encoding system and Fresnel doublerandom phase encoding system，the research illuminate the recording process andreconstruction principle of object light. This research has introduces the phase recoveryalgorithm that have used in this implementation process, Completed the experimentalsimulation.about the4f double random phase encoding, Fresnel double random phaseencoding, Fresnel holographic and phase recovery algorithm.Sencondly, we choose the Fresnel holography method to solve the problem thatencrypted image is a complex image neither good for storage nor facilitate fortransmission by use optical image encryption method. To solve this problem, the plaintextencrypted into one digital hologram image, This method recording the holographic imagein the form of the digital data, this can convenient for ciphertext image storage andtransmission. We choose Arnold transformation combined with Fresnel holography,completed the Fresnel hologram pixel scrambling, when combined of the twomethods,this method can increase the number of keys to improve system security. finally,the research use the HRO subtraction methods to improve the quality of Fresnelholography, completion of the single image encryption.Thirdly, a new multi-image encryption method has been proposed based on the GSphase retrieval algorithm and Fresnel transform presents to simplify the experimentaldevice and improve the algorithm simplicity and security. Each plaintext is encoded to aphase only function by phase retrieval algorithm in Fresnel transform domain to complete the encryption process. When set the initial phase mask sequentially placed on the inputplane and put the iterated phase mask on Frequency spectrum plane we can achieved thecorrect ciphertext in output plane and completed the decryption process by use plane waveillumination the phase mask. This method has the advantage that not only thetransformation of the wavelength and the Fresnel diffraction distance can as secret key,and the implementation does not need to use the optical lens so can simplify the devices.When we verify the feasibility of the algorithm find that the algorithm applicable to colorimage encryption and complete the algorithm’s promotion.At last, the research has proposed the optical devices of the two encryptionmethod,at same time to verify the validity and safety by using programming experimentsimulation on Matlab software interface.