BrowserUk,

This is an observation sometime from 2005-2008. My handle on PM is because of working on this project at the time I joined, but I have little to due with the project now. It was a project to backup Terabytes of encrypted files to geographically distant off-site computer centers using 'rsync' in close to 'real-time'. The client's goal was that 'rsync' not work with the real files, but only with encrypted files which sort of negates the value of using 'rsync'. While we looked at several methods for getting a value for naming the encrypted files, we ran tests of several different sets of 1 million encrypted files and the following table is an average.

  Technique          Duplicates

     MD5                5,701
     crc32             26,323
     SimCRC64              17       Simple 8 byte ^ of file (very fast
+)
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I can't say these results would be the same anywhere else, but when I started testing, I was sure that MD5 would be the most unique, and that's why we ran the tests several times with different file sets. I don't know if the encryption algorithm affected the results and don't know it the unencrypted files would give similiar results or not. I just didn't expect the results!

I only bring this up because I think you started out with the same assumption about MD5, but maybe there is a better starting point and maybe not.

Thank you