title: How to include the CRC32 of a file into it at a specific place?
body: <p>I am working on a data generator in order to generate binary files into a closed system for which we assume there is no risk of external attacks nor any malicious intent.</p>
  
  <p>The idea is to find a way for these binaries to contain a quick and relatively reliable way to ensure they have not been accidentally corrupted in the toolchain so the final receiver of this binary can check the file integrity without any additional resource (such as file.sha1 containing the checksum).</p>
  
  <p>As it may affect the solution, I must tell that the binary file can be 1 kB up to maybe 300 MB of data. There is a specific position in the file where I can place a checksum of any fixed length for all files. The position is already defined I can not change it but I can change the length.</p>
  
  <p>So if the solution is to include 128 bytes of data at this position in order to suit any possible case then all binaries will contain this byte length at this position.</p>
  
  <p>As it would be impossible to include a cryptographic hash of the file into it without the need to cut it off before checking, I read that CRC32 is a good way to achieve this goal. I have also took knowledge of utilities such as "spoof" or "CRC manipulator" but they seem not to satisfy my case.</p>
  
  <p>Here is a quick example of what I need. Let's consider a binary file:</p>
  
  <pre><code>               This position will never change
                 v
  1011101100010010000000010110011100100110
                 ^^^^^^^^
                 This is the fixed-length part dedicated to file integrity check
  </code></pre>
  
  <p>I would like to find a way to insert the right checksum so the complete file including the checksum has the overall same checksum. Maybe a known program already does this ?</p>
  
  <p>Thanks for your support</p>