Optical Cryptosystems. Naveen K. Nishchal
transformed and the order of transformation.
% PT is the plaintext% Phase_mask1 and Phase_mask2 are the two random phase masks to be used as the keys.PT=imread(’D:\Program\images\godisgreat.bmp’);%reading the image to be encryptedPT=double(PT(:,:,1));PT=PT./max(max(PT));figure;imagesc(abs(PT));colormap(gray);title(’original input image’);%defining the two random phase masks for the two keys[M,N]=size(PT);phase_values1=rand(M);phase_values2=rand(M);phase_mask1=exp(j*2*pi*phase_values1);%First Keyphase_mask2=exp(j*2*pi*phase_values2);%Second Key%%%%%Encryption%First Fractional Fourier transform with fractional order 0.25A=PT.*phase_mask1;A=frt(A,0.25);%Second Fractional Fourier transform with fractional order 0.45B=A.*phase_mask2;B=frt(B,0.45);%ciphertextfigure;imagesc(abs(B));colormap(gray);title(’encrypted image’);%%%%%decryptionD=frt(frt(B,−0.45).*conj(phase_mask2),−0.25);figure;imagesc(abs(D));colormap(gray);title(’decrypted image’);
IV. Gyrator transform
functionqt=gyrator(q,a)% Matlab code for fast algorithm of discrete gyrator transform%qis an input signal and a is rotation angle% Direct DGT[M,N]=size(q);mm=((0:M−1)-(M)/2)/sqrt(M);nn=((0:N−1)-(N)/2)/sqrt(N);[x,y]=meshgrid(nn,fliplr(mm));[u,v]=meshgrid(mm,fliplr(nn));p1=exp(−2*j*pi*x.*y*tan(a/2));p2=fftshift(exp(−2*j*pi*u.*v*sin(a)));qt=p1.*(ifft2(fft2(p1.*q).*p2));end
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