Can I use part of MD5 hash for data identification?

Posted by sharptooth on Stack Overflow See other posts from Stack Overflow or by sharptooth
Published on 2010-05-06T09:57:25Z Indexed on 2010/05/06 10:08 UTC
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I use MD5 hash for identifying files with unknown origin. No attacker here, so I don't care that MD5 has been broken and one can intendedly generate collisions.

My problem is I need to provide logging so that different problems are diagnosed easier. If I log every hash as a hex string that's too long, inconvenient and looks ugly, so I'd like to shorten the hash string.

Now I know that just taking a small part of a GUID is a very bad idea - GUIDs are designed to be unique, but part of them are not.

Is the same true for MD5 - can I take say first 4 bytes of MD5 and assume that I only get collision probability higher due to the reduced number of bytes compared to the original hash?

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