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new tutorial: why the blog

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nihilist 2025-04-30 11:23:16 +02:00
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opsec/steghide/index.html
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@ -83,7 +83,7 @@
<a href="apod20240824.jpg" style="text-align: center"><div><img src="apod20240824.jpg" style="width:250px;"></div></a>
<p>Our example file to hide is going to be <a href="https://bitcoin.org/bitcoin.pdf">Bitcoin: A Peer-to-Peer Electronic Cash System</a>, the original paper by Satoshi Nakamoto.</p>
<p>As mentioned above, the cover image must be larger than the file you wish to embed, <b>as a rule of thumb your coverfile should be 20 times larger</b>. (Hint: you can split larger files with tools like tar or 7z into smaller fragments to embed into a whole collection of cover files.) We can check how many bytes steghide can embed by using <code class="nim">steghide info <i>file</i></code>. In our case, it tells us that it can embed 232 KB and asks whether an attempt should be made at reading embed data without extracting. As there is nothing embedded yet, we decline with <kbd>n</kbd>.</p>
<p>As mentioned above, the cover image must be larger than the file you wish to embed, <b>as a rule of thumb your coverfile should be 20 times larger</b>. (Hint: you can split larger files with tools like tar or 7z into smaller fragments to embed into a whole collection of cover files.) We can check how many bytes steghide can embed by using <code class="nim">steghide info <i>file</i></code>. In our case, it tells us that it can embed 232 KB and asks wheter an attempt should be made at reading embed data without extracting. As there is nothing embedded yet, we decline with <kbd>n</kbd>.</p>
<pre><samp>"apod20240824.jpg":
format: jpeg
@ -100,7 +100,7 @@ Try to get information about embedded data ? (y/n)
<div><b>WARNING: changing the output file in anyway will make the embedded file irretrievable. This is especially important for every form of lossy compression!</b></div>
<p>Now let's try to extract the file we've just hid. For this, use <code class="nim">steghide embed -sf <i>input</i></code></p>. This will prompt you for the passphrase. Enter it, and the contents will be extracted into the working directory. In our case we will be asked whether we want to overwrite the file with the same name that already exists. (You can suppress this warning with <code class="nim">-f</code> or by specifying an alternative output destination with <code class="nim">-xf</code>. Here, I used the later so we can confirm the files to be identical with md5sum:
<p>Now let's try to extract the file we've just hid. For this, use <code class="nim">steghide embed -sf <i>input</i></code></p>. This will prompt you for the passphrase. Enter it, and the contents will be extracted into the working directory. In our case we will be asked wheter we want to overwrite the file with the same name that already exists. (You can suppress this warning with <code class="nim">-f</code> or by specifying an alternative output destination with <code class="nim">-xf</code>. Here, I used the later so we can confirm the files to be identical with md5sum:
<pre><samp>d56d71ecadf2137be09d8b1d35c6c042 bitcoin.pdf
d56d71ecadf2137be09d8b1d35c6c042 output.pdf</samp></pre>