RSA algorithm for image encryption

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Parveiz Lone
Parveiz Lone 2020-9-5
评论： Kajal Chawla 2025-7-15
c
lc;
clear all;
format longE
disp('RSA algorithm');
p=input('Enter the prime no. for p: ');%23
q=input('Enter the prime no. for q: ');%13
n=p*q;
fprintf('\n n=%d',n);
phi=(p-1)*(q-1);
fprintf('\n phi(%d) = %d',n,phi);
e=input('\n Enter the value for e relatively prime to phi:');%23
%% find inverse for e
for d=1:phi
f=mod(e*d,phi);
if f==1
break
end
end
c=[2 254 123;214 231 189;241 253 3]% image matrix
A=[];
B=[];
%% cipher image
for i=1:3
for j=1:3
A(i,j)=mod(c(i,j)^(e),n);
end
end
%% decrypted image
for i=1:3
for j=1:3
B(i,j)=mod(A(i,j)^(d),n);
end
end

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回答（1 个）

Madhu
Madhu 2024-2-21
编辑：Walter Roberson 2024-2-21
Dear Parveiz Lone
still you have the same doubt? Follow this code as it is.
img=imread('Lenna.jpg'); %Reading an RGB image
img=rgb2gray(img); % converting RBG image into grayscale image
img=imresize(img,[128,128]); % Resizing the image
img=reshape(img,1,numel(img)); % Reshaping 2D array into 1D array
img=double(img);
cip=zeros(1,numel(img));
ct=zeros(1,numel(img));
primenumbers=primes(1000);
p=primenumbers(randi(numel(primenumbers),1,1));
q=primenumbers(randi(numel(primenumbers),1,1));
n=p*q;
phi=(p-1)*(q-1);
e = randi([2, phi-1]);
while (gcd(e,phi)~=1)
x = randi([2, phi-1]);
if gcd(x, phi) == 1
e = x;
end
end
d=multiplicativeInverse(e, phi);
for i=1:1:numel(img)
cip(i)=powermod(img(i),e,n);
ct(i)=mod(cip(i),255); %Limiting cip to values less than 255.
end
ct=reshape(ct,128,128);
imshow(ct,[]);
pt=zeros(1,numel(img));
for i=1:1:numel(img)
pt(i)=powermod(cip(i),d,n);
end
pt=reshape(pt,128,128);
imshow(pt,[]);
function result = multiplicativeInverse(a, m)
[g, result, ~] = extended_gcd(a, m);
if g ~= 1
error('Inverse does not exist.');
end
result = mod(result, m);
end
function [g, x, y] = extended_gcd(a, b)
% Extended Euclidean Algorithm
if b == 0
g = a;
x = 1;
y = 0;
else
[g, x, y] = extended_gcd(b, mod(a, b));
temp = x;
x = y;
y = temp - floor(a/b) * y;
end
  3 个评论
显示 1更早的评论
Madhu
Madhu 2024-2-21
Further any doubts mail me to msnaidu417@gmail.com
Kajal Chawla
Kajal Chawla 2025-7-15
Respected mam, I have gone through your code and have a doubt regarding decryption of this code. When a reciever wants to decrypt the image he has the access to encrypted image matrix that is ct, but decryption code needs the matrix cip. Can you please clarify that?

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