title: Self-referencing MD5 file
body: <p>I'm developing a program that needs to load and save data in external files, I have been searching for options and I have chosen to save the data in a binary file.</p>
  
  <p>As I don't want that someone could edit the file easily, I thought about writing in the first line of the file, its md5 sum. In this case, if some data of the file is changed, the sum won't match the one of the first line.</p>
  
  <p>The problem I find then is that if I calculate the MD5, and after that I write the info inside the file, it's obvious that the sum will be different, so, how could I sort this?</p>
  
  <p>If you sugest me a better option than the sum, it will be equally accepted.</p>
  
  <p>Thanks in advance.</p>