decrypt_vigenere.m

loading a text file from a directory to your workspace in matlab

%% Coincidence Counting Program
close all;
clear all;
clc;
%% Read the cyphered text from a *.txt file
text_input = loadtext('Decrypt_3.txt');
%% Remove the blanks from input text.

index = find(text_input ~= ' ');
text = text_input(index);

%% 
len = length(text);
shmax = len-1;

count=0;
results = zeros(shmax,3);

for m=1:shmax
    
    % Rotate text relative to itself by m spots
    teststr=[text(m+1:end) text(1:m)];
    
    % Count number of matches
    for i=1:len
        if teststr(i)==text(i)
            count=count+1;
        end
    end
    
    results(m,1) = m;
    results(m,2) = count;
    
    % Normalize the count by the length of the string
    results(m,3) = count/len;
    
    % Reset count for next iteration
    count=0;
end


% What does this do?  Try to make sense of it!
results
max_m=find(max(results(:,3))==results(:,3))
max_norm_count=max(results(:,3))

f=find(results(:,2)>19);
results(f,:)