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//////////////////////////////////////////
// //
//(a) Encrytion scheme of hill cipher //
// //
//////////////////////////////////////////
//PLaintext
pt = "CAT"
disp("Plaintext: ")
disp(pt)
l = length(pt)
pt = strsplit(pt)
a = ascii("A")
pt_mat = []
//Taking A=0,B=1,C=2,etc.
for i=1:l
pt_mat(i,1)=ascii(pt(i,1))-a
end
disp("Plaintext matrix:")
disp(pt_mat)
//Key matrix
key_mat = [6 24 1; 13 16 10;20 17 15]
disp("Encryption Key matrix:")
disp(key_mat)
//ciphertext matrix
ct_mat = key_mat * pt_mat
disp("Product: ")
disp(ct_mat)
[r,c]=size(ct_mat)
//Taking mod for correct conversion
for i=1:r
ct_mat(i,1) = modulo(ct_mat(i,1),26)
end
disp("Ciphertext matrix: ")
disp(ct_mat)
disp("Ciphertext: ")
//Conversion of code to letters
ct=[]
for i=1:r
ct(i,1) = ascii(ct_mat(i,1)+a)
end
ct = strcat(ct)
disp(ct)
//////////////////////////////////////////
// //
//(b) Decrytion scheme of hill cipher //
// //
//////////////////////////////////////////
//Ciphertext
disp("Ciphertext: ")
disp(ct)
l = length(ct)
ct = strsplit(ct)
a = ascii("A")
ct_mat = []
//Taking A=0,B=1,C=2,etc.
for i=1:l
ct_mat(i,1)=ascii(ct(i,1))-a
end
disp("Ciphertext matrix:")
disp(ct_mat)
//Key matrix for decryption (inverse of encryption key matrix)
key_mat = [8 5 10; 21 8 21;21 12 8]
disp("Decryption Key matrix:")
disp(key_mat)
//ciphertext matrix
pt_mat = key_mat * ct_mat
disp("Product: ")
disp(pt_mat)
[r,c]=size(pt_mat)
//Taking mod for correct conversion
for i=1:r
pt_mat(i,1) = modulo(pt_mat(i,1),26)
end
disp("Plaintext matrix: ")
disp(pt_mat)
disp("Plaintext: ")
//Conversion of code to letters
pt=[]
for i=1:r
pt(i,1) = ascii(pt_mat(i,1)+a)
end
pt = strcat(pt)
disp(pt)
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