% CEASAR
%Taking the input from the users
text=input('Enter the plain text.','s');
offset=input('Enter the offset value.');
ciphertext=text;

for i=1:length(text)
    temp = double(text(i));
    if(temp>=65 && temp<=90)
        %Converting character into ASCII value
        currascii=temp-65;
        %Shifting values by offset
        encryascii=mod(currascii+offset,26);
        %Converting ASCII value back into character
        ciphertext(i)=char(encryascii+65);
    else
        currascii=double(text(i))-97;
        encryascii=mod(currascii+offset,26);
        ciphertext(i)=char(encryascii+97);
    end
end
disp("After encryption:");
disp(ciphertext);

%Decryption: Subtracting offset from ciphertext to decipher it.
deciphertext=ciphertext;
for i=1:length(ciphertext)
    temp = double(ciphertext(i));
    if(temp>=65 && temp<=90)
        currascii=temp-65;
        decryascii=mod(currascii-offset,26);
        deciphertext(i)=char(decryascii+65);
    else
        currascii=double(ciphertext(i))-97;
        decryascii=mod(currascii-offset,26);
        deciphertext(i)=char(decryascii+97);
    end
end
disp(deciphertext);


% MONOALPHABETIC
clc;
clear all;
close all;
key=randperm(26);
text='ATTACK';
ciphertext=text;
%Encryption
for i=1:length(text)
    %Subtracting 64 to get index in range [1,26]
    charIndex=double(text(i))-64;
    %mapping characters from text to key
    ciphertext(i)=char(key(charIndex)+64);
end
disp(ciphertext);

%Decryption
deciphertext=ciphertext;
for i=1:length(ciphertext)
    charIndex=double(ciphertext(i))-64;
    %finding the index for ciphered character in the array key
    textIndex=find(key==charIndex);
    %adding 64 to map ciphered character back into original character
    deciphertext(i)=char(textIndex+64);
end
disp(deciphertext);



% HILL
clc;
clear all;
close all;
text='ATTACKNOW';
n=2;
while(mod(length(text),n)~=0)
    text=text+"Z";
    text=char(text);
end
%Encryption
key=[2 1; 3 4];

text=reshape(text,[length(text)/n,n]);

text1=transpose(text);
text1=double(text1)-65;

ciphertext=mod(key*text1,26);
ciphertext=char(ciphertext+65);
ciphertext=transpose(ciphertext);
ciphertext=reshape(ciphertext,1,[]);

disp(ciphertext);

%Decryption

key1=det(key);
for i=1:1:25
    a = mod(key1*i,26);
    if a==1
            k2=i;
    end
end

key_inverse=round(mod(k2*adjoint(key),26));

ciphertext=double(ciphertext)-65;

ciphertext=reshape(ciphertext,length(ciphertext)/n,[]);
ciphertext=transpose(ciphertext);

deciphertext=mod(key_inverse*ciphertext,26);
deciphertext=transpose(deciphertext);
deciphertext=reshape(deciphertext,1,[]);
deciphertext=char(deciphertext + 65);
disp(deciphertext);




%COLUMNAR
text=input('Enter the message:','s');
n=input('Enter a number:');

while(mod(length(text),n)~=0)
    text=text+"Z";
    text=char(text);
end

text=upper(text);
key=randperm(n);
text=reshape(text,[length(text)/n,n]);

ciphertext=text;

[rows,cols]=size(text);
for i=1:rows
    for j=1:cols
        ciphertext(i,j)=text(i,key(j));
    end
end
ciphertext=transpose(ciphertext);
ciphertext=reshape(ciphertext,1,[]);
disp(ciphertext);
%Decryption
ciphertext=reshape(ciphertext,cols,[]);
ciphertext=transpose(ciphertext);
deciphertext=ciphertext;
for i=1:rows
    for j=1:cols
        deciphertext(i,j)=ciphertext(i,find(key==j));
    end
end
deciphertext=reshape(deciphertext,1,[]);
disp(deciphertext);



%DOUBLE COLUMNAR
text=input('Enter the message:','s');
n1=input('Enter a number:');

while(mod(length(text),n1)~=0)
    text=text+"Z";
    text=char(text);
end

text=upper(text);
n2=length(text)/n1;
key1=randperm(n1);
key2=randperm(n2);
text=reshape(text,n1,[]);

ciphertext=text;

[rows,cols]=size(text);
for i=1:rows
    for j=1:cols
        ciphertext(i,j)=text(key1(i),key2(j));
    end
end
ciphertext=transpose(ciphertext);
ciphertext=reshape(ciphertext,1,[]);
disp(ciphertext);
%Decryption
ciphertext=reshape(ciphertext,cols,[]);
ciphertext=transpose(ciphertext);
deciphertext=ciphertext;
for i=1:rows
    for j=1:cols
        deciphertext(i,j)=ciphertext(find(key1==i),find(key2==j));
    end
end
deciphertext=reshape(deciphertext,1,[]);
disp(deciphertext);




% AUTOKEY
text="ATTACKNOW";
key=round(rand(1)*26);

key=char(key+65)+text;
key=char(key);
text=char(text);
ciphertext=text;
for i=1:length(text)
    a=double(text(i))-65;
    b=double(key(i))-65;
    ciphertext(i)=char(mod(a+b,26)+65);
end
disp(ciphertext);
%Decryption

deciphertext=ciphertext;
for i=1:length(ciphertext)
    a=double(ciphertext(i))-65;
    b=double(key(i))-65;
    deciphertext(i)=char(mod(a-b,26)+65);
end
disp(deciphertext);


% VERNAM
text='ATTACKNOW';
key=randperm(26,length(text));

text=double(text)-65;
ciphertext=bitxor(text,key);
%ciphertext=mod(ciphertext,26);
ciphertext=char(ciphertext+65);
disp(ciphertext);
%Decryption

ciphertext=double(ciphertext)-65;
deciphertext=ciphertext;
for i=1:length(ciphertext)
    deciphertext(i)=bitxor(key(i),ciphertext(i));
end
%deciphertext=mod(deciphertext,26);
deciphertext=char(deciphertext+65);
disp(deciphertext);




% VIGNERE
text='ATTACKNOW';
n=3;
key=randperm(26,3);
key=char(key+65);
while (length(key)<length(text))
    key=key+string(key);
    key=char(key);
end
key=resize(key,length(text));
ciphertext=mod(double(text)-'A'+double(key)-'A',26);
ciphertext=char(ciphertext+'A');
disp(ciphertext);
%Decryption
deciphertext=ciphertext;
deciphertext=mod(double(ciphertext)-'A'-double(key)+'A',26);
deciphertext=char(deciphertext+'A');
disp(deciphertext);



% EXTENDED EUCLIDIAN
num1=input('Enter a number:');
num2=input('Enter a number:');
s1=1;
s2=0;
t1=0;
t2=1;
while(num2~=0)
    r=mod(num1,num2);
    q=floor(num1./num2);

    num1=num2;
    num2=r;

    s=s1-q*s2;
    t=t1-q*t2;
    s1=s2;
    s2=s;
    t1=t2;
    t2=t;
end
disp("GCD = " + num1);
disp("s = " + s1);
disp("t = " + t1);




% PLAYFAIR
clear all;
key='SEKIRO';
text='SHADOWSDIETWICEE';
text=upper(text);

for i=1:length(text)
    if(text(i)=='J')
        text(i)='I';
    end
end
for i=1:length(text)-1
    if(text(i)==text(i+1))
        temp=text(i+1:length(text));
        text(i+1)='X';
        text=resize(text,i+1);
        text=string(text);
        text=text+temp;
        text=char(text);
    end
end

if(mod(length(text),2)~=0)
    text=text+"Z";
    text=char(text);
end

remainingchars=1:1:26;
remainingchars(10)=0;

for i=1:26
    for j=1:length(key)
        if(remainingchars(i)==(double(key(j))-64))
            remainingchars(i)=0;
        end
    end
end

matrix(5,5)=0;

k=1;
for i=1:5
    for j=1:5
        matrix(i,j)=double(key(k))-64;
        k=k+1;
        if(k>length(key))
            break;
        end
    end
    if(k>length(key))
        break;
    end
end

ch=1;
for i=1:5
    for j=1:5
        if(matrix(i,j)~=0)
            continue;
        end
        while(remainingchars(ch)==0)
            ch=ch+1;
        end
        matrix(i,j)=ch;
        ch=ch+1;
    end
end

textnum=double(text)-64;

ar1=0;
ar2=0;
ac1=0;
ac2=0;
ciphertext=textnum;
for k=1:2:length(text)-1
    p1=find(matrix==textnum(k));
    r1=mod(p1,5);
    c1=ceil(p1./5);
    p2=find(matrix==textnum(k+1));
    r2=mod(p2,5);
    c2=ceil(p2./5);

    if(r1==0)
        r1=5;
    end

    if(r2==0)
        r2=5;
    end

    if(r1==r2)
        ac1=mod(c1+1,5);
        if(ac1==0)
            ac1=5;
        end
        ac2=mod(c2+1,5);
        if(ac2==0)
            ac2=5;
        end
        ar1=r1;
        ar2=r2;
    elseif(c1==c2)
        ar1=mod(r1+1,5);
        if(ar1==0)
            ar1=5;
        end
        ar2=mod(r2+1,5);
        if(ar2==0)
            ar2=5;
        end
        ac2=c2;
        ac1=c1;
    else
        ar1=r1;
        ac1=c2;
        ar2=r2;
        ac2=c1;
    end
    ciphertext(k)=matrix(ar1,ac1);
    ciphertext(k+1)=matrix(ar2,ac2);
end
disp(char(ciphertext+64));
%Decryption

br1=0;
br2=0;
bc1=0;
bc2=0;
deciphertext=ciphertext;
for k=1:2:length(ciphertext)-1
    p1=find(matrix==ciphertext(k));
    r1=mod(p1,5);
    c1=ceil(p1./5);
    p2=find(matrix==ciphertext(k+1));
    r2=mod(p2,5);
    c2=ceil(p2./5);
    ciphertext(k)=0;
    ciphertext(k+1)=0;

    if(r1==0)
        r1=5;
    end

    if(r2==0)
        r2=5;
    end

    if(r1==r2)
        bc1=mod(c1-1,5);
        if(bc1==0)
            bc1=5;
        end
        bc2=mod(c2-1,5);
        if(bc2==0)
            bc2=5;
        end
        br1=r1;
        br2=r2;
    elseif(c1==c2)
        br1=mod(r1-1,5);
        if(br1==0)
            br1=5;
        end
        br2=mod(r2-1,5);
        if(br2==0)
            br2=5;
        end
        bc2=c2;
        bc1=c1;
    else
        br1=r1;
        bc1=c2;
        br2=r2;
        bc2=c1;
    end
    deciphertext(k)=matrix(br1,bc1);
    deciphertext(k+1)=matrix(br2,bc2);
end
disp(char(deciphertext+64));



%FIESTEL
clear all;
text='SHADOWSDIETWICE';
text=upper(text);

if(mod(length(text),2)~=0)
    text=text+"Z";
    text=char(text);
end

lefthalf=text(1:length(text)/2);
righthalf=text(length(text)/2+1:length(text));

cipherrighthalf=lefthalf;
key=randperm(26,length(text)/2);

righthalf=double(righthalf)-64;
cipherlefthalf=bitxor(righthalf,key);
ciphertext=string(char(cipherlefthalf+64))+cipherrighthalf;
disp(ciphertext);

%Decryption
ciphertext=char(ciphertext);
lefthalf=ciphertext(1:length(ciphertext)/2);
righthalf=ciphertext(length(ciphertext)/2+1:length(ciphertext));

decipherleft=righthalf;
lefthalf=double(lefthalf)-64;
decipherright=bitxor(lefthalf,key);
deciphertext=decipherleft+string(char(decipherright+64));
disp(deciphertext);




% FAST EXPONENTIATION
clear all;
x2=input('Enter the base of the number:');
x1=input('Enter the exponent of the number');
n=input('Enter the value for mod function:');
bits=dec2bin(x1);
result=x2;
if(length(bits)==1)
    result=mod(x2^x1,n);
end

for i=2:length(bits)
    if(bits(i)=='1')
        result=mod(result^2,n);
        result=mod(result*x2,n);
    else
        result=mod(result^2,n);
    end
end
disp(result);