create Sbox for encryption

Good day,

How can I convert a series of 64-bit to (16 decimal) vector to create sbox,

for example, I need the output like this ... sbox=[12 5 6 11 9 0 10 13 3 14 15 8 4 7 1 2];

key input as (64-bit binary)

I'm write the below code

function s_out=updatesbox(key)

sbox=[];

for i=1:4:64

sbox[] = bin2dec(key(i:i+3)+1);

end

thanks

Answer 1

[Divyam]

Hi @Hussain,

You should add input validation to your code to ensure that the key is a string of 64 characters. The offset used in the "bin2dec" function is unnecessary considering that it does not add any value to the crytogrpahic strength.

To solve the indexing problem, you can use direct indexing with to correctly place each decimal value in the "sbox" array.

function s_out = updatesbox(key)
    % Ensure the key is a string of 64 characters
    if length(key) ~= 64
        error('Key must be a 64-bit binary string.');
    end

    sbox = zeros(1, 16); % Preallocate space for the S-box
    for i = 1:4:64
        % Convert 4-bit binary substring to decimal
        decimal_value = bin2dec(key(i:i+3));
        % Add 1 to the decimal value to match your desired output
        sbox((i+3)/4) = decimal_value;
    end
    
    s_out = sbox;
end

% Sample 64-bit binary input
key = '1100101011110000101010111100110010101011110000101010111100110010';

% Call the updatesbox function
sbox_output = updatesbox(key);

% Display the resulting S-box
disp('Generated S-box:');

Generated S-box:

disp(sbox_output);

    12    10    15     0    10    11    12    12    10    11    12     2    10    15     3     2