LSB steganography : i can't extract the original messages

Question

ARJUN K P 2015-5-16

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/217072-lsb-steganography-i-can-t-extract-the-original-messages

评论： Walter Roberson 2015-5-17

the code is:

embedding code:

c = imread('lena.jpg');
    message = 'hellokarthick';
    message = strtrim(message);
    m = length(message) * 8;
    AsciiCode = uint8(message); 
    binaryString = transpose(dec2bin(AsciiCode,8));
    binaryString = binaryString(:);
    N = length(binaryString);
    b = zeros(N,1); %b is a vector of bits
    for k = 1:N
        if(binaryString(k) == '1')
            b(k) = 1;
        else
            b(k) = 0;
        end
    end
    s = c;
    height = size(c,1);
    width = size(c,2);
    k = 1;
    for i = 1 : height
        for j = 1 : width
             LSB = mod(double(c(i,j)), 2);
            if (k>m || LSB == b(k))
                s(i,j) = c(i,j);
                else
                    s(i,j) = c(i,j) + b(k);
            k = k + 1;
        end
        end
    end
     imwrite(s, '111.jpg');

Extraction:

    for i = 1 : height
        for j = 1 : width
            if (k <= m)
                b(k) = mod(double(s(i,j)),2);
                k = k + 1;
            end
        end
    end
    binaryVector = b;
    binValues = [ 128 64 32 16 8 4 2 1 ];
    binaryVector = binaryVector(:);
    if mod(length(binaryVector),8) ~= 0
        error('Length of binary vector must be a multiple of 8.');
    end
    binMatrix = reshape(binaryVector,8,100);
    display(binMatrix);
    textString = char(binValues*binMatrix);    
    disp(textString);

The output is:

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Answer 1

Geoff Hayes 2015-5-16

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/217072-lsb-steganography-i-can-t-extract-the-original-messages#answer_179350

在 MATLAB Online 中打开

Arjun - I suspect the problem is with the line

imwrite(s, '111.jpg');

You are saving s, the image with the secret message, as a jpeg which is a lossy compression method. This means that you are most likely losing information when you save s in this manner. You can prove this by comparing s with that data which is returned by

sp = imread('111.jpg');

s and sp are most likely not identical and so the LSB extraction method (from above) will fail.

I think that you can do one of two things - save the image as bitmap or set the compression to none as

imwrite(s,'111.jpg','Compression','none');

Try the above and see what happens!