<p>I was wondering if you know somewhere where I can find information on how to build a signature file for docuement retrieval. <br>
Do you know if there is some code out there that I can use or look at?<br>
I have to create a signature file in C++ under linux platform.<br>
<br>
<b>UPDATE: Sorry, I appreciatte the help but I was refering to signature files not as a way to validate documents but as a way of indexing documents.<br><br><br>
<a href="http://en.wikipedia.org/wiki/Signature_files" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Signature_files</a><br><br><br></b>
Any help will be greatly appreciated.</p>

<p>Thanks,</p>

md5sum
might be what you are looking for. Source code for generating md5 signatures is available if you Google around.
From Wikipedia:
Because almost any change to a file
  will cause its MD5 hash to also
  change, the MD5 hash is commonly used
  to verify the integrity of files
  (i.e., to verify that a file has not
  changed as a result of file transfer,
  disk error, meddling, etc.). The
  md5sum program is installed by default
  in most Unix, Linux, and Unix-like
  operating systems or compatibility
  layers. BSD variants (including Mac OS
  X) have a similar utility called md5.
  Versions for Microsoft Windows do
  exist.