disp('******************************************************************')
disp('Computes x^b mod n according to the square and multiply algorithm ')
disp('******************************************************************')
disp(' ')
disp(' ')
t=input ('If you want to RSA cipher press -> 1 RSA decipher -> 0 ...');
switch(t)
  case {1}
     x=input ('Give me x= ');
     b=input ('Give me b= ');
     n=input ('Give me n= ');
     binary1=dec2bin(b);
     l=length(dec2bin(b));
     z=1;
     for i=1:1:l
        z=mod(z.*z,n);
        itt=i;
        if binary1(i)=='1'
           z=mod(z.*x,n);
        end   
     end
     z
  case{0}
     x=input ('Give me x= ');
     a=input ('Give me a= ');
     n=input ('Give me n= ');
     binary1=dec2bin(a);
     l=length(dec2bin(a));
     z=1;
     for i=1:1:l
        z=mod(z.*z,n);
        itt=i;
        if binary1(i)=='1'
           z=mod(z.*x,n);
        end   
     end
     z
  otherwise
     disp('Unknown selection')
  end
 disp('Implementation by Diomedes Kastanis')