%% 1FLAMEN6 - decode "thefm_auriskeyfile" message
% Written by OnTheMF

tall            = 1; % Tall flame bit-value
tiny            = 0; % Short flame bit-value
ribbon_short    = 0; % Short ribbon bit-value
ribbon_long     = 1; % Long ribbon bit-value

%% Dataset

% Key with ribbons
rbn_l2r = [ ribbon_short, ribbon_long, ribbon_long,...
            ribbon_short, ribbon_long, ribbon_short ];

% Outer top segment
ot_l2r = [ tiny, tiny, tall, tall, tiny, tall, tall, tiny, tiny, tall,...
           tall, tall, tiny, tiny, tall, tall, tiny, tall ];
% Outer right segment
or_t2b = [ tiny, tiny, tall, tall, tall, tall, tiny, tiny, tiny, tall,...
           tiny, tall ];
% Outer bottom segment
ob_r2l = [ tiny, tiny, tall, tall, tall, tall, tall, tiny, tall, tall,...
           tiny, tall, tiny, tiny, tiny, tall ];
% Outer left segment
ol_b2t = [ tiny, tall, tall, tiny, tall, tall, tiny, tall ];
% Inner top segment
it_l2r = [ tiny, tall, tall, tiny, tall, tall, tiny, tall, tall, tiny,...
           tall, tiny, tiny, tiny, tall, tiny, tall, tall, tiny, tall,...
           tall, tiny, tall, tall, tiny, tiny, tall, tall];
% Inner right segment
ir_t2b = [ tall, tall, tiny, tall, tall, tall, tall, tall, tiny, tall,...
           tall, tiny, tall, tall, tiny, tall, tall, tall, tall, tall,...
           tiny, tiny, tall, tiny ];
% Inner bottom segment
ib_r2l = [ tall, tiny, tiny, tiny, tall, tall, tall, tiny, tiny, tiny,...
           tall, tiny, tall, tall, tiny, tall, tall, tall, tall, tall,...
           tiny, tall, tall, tall, tall, tall, tiny, tall, tall, tall,...
           tall, tall, tiny ];
% Inner left segment       
il_b2t = [ tiny, tall, tall, tall, tiny, tiny, tall, tall, tiny, tall,...
           tall, tiny, tall ];

% Reverse our segments for easy manipulation
ot_r2l = fliplr(ot_l2r);
or_b2t = fliplr(or_t2b);
ob_l2r = fliplr(ob_r2l);
ol_t2b = fliplr(ol_b2t);
it_r2l = fliplr(it_l2r);
ir_b2t = fliplr(ir_t2b);
ib_l2r = fliplr(ib_r2l);
il_t2b = fliplr(il_b2t);

%% Decode keyfile message
encrypted_track = [ib_l2r, il_t2b, ir_t2b, it_r2l, ot_r2l, ob_l2r];

% Skip first bit
decrypted_track = vectorxor(encrypted_track(2:end), rbn_l2r);

% Generate indexes for every fifth bit (circular buffer)
message_indices = mod((0:(length(decrypted_track)-1)) * 5, length(decrypted_track)) + 1;

% Get the message bits in the correct order
message_data = decrypted_track(message_indices);

% Decode and display message
decodebacon(message_data)

%% Helper functions
% xor a vector or matrix with a given key vector
function [ret] = vectorxor(x,key)
    % Pre-allocate return variable
    ret = zeros(size(x,1),size(x,2));

    % Generate 1:1 vector for xor function
    copies = ceil(size(x, 2) / length(key));
    xkey = repmat(key, 1, copies);
    xkey = xkey(1:size(x, 2));

    % Iterate through each row of input data
    for i = 1:size(x,1)
        ret(i,:) = xor(x(i,:), xkey);
    end
end

% Decode a Bacon v2 string (base 26) - invalid characters mapped to space
function [ret] = decodebacon(x)
    letters = 'abcdefghijklmnopqrstuvwxyz ';
   
    % Only decode 5-bit sequences
    vals = x(1:end - mod(length(x), 5));
   
    % Convert to base 10 values
    dec = sum(reshape(vals, 5, length(vals) / 5) .* (2 .^ (4:-1:0))')';
   
    % Return corresponding string
    ret = letters(min(dec'+1, length(letters)));
end