Userfriendly but secure algorithm for anonymising IIS log files
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I have a set of IIS log files that I'd like to publish for a research study.

However, these contain some sensitive information that I would like to anonymise, eg:

    UserName=XXXX65

I'd like to use an algorithm that retains some "user friendly"-ness for visual inspection of the log files, but which is also secure enough it is impossible / impractical to derive the original UserNames.

I can't just **** out all the UserNames, since it is important to be able to correlate requests from the same username across the logs.

Using SHA1 hashing gives me something like

     UserName=AD5CBF0BA0A8646EBDBA6BE1B5DA4FCB1F385D39

which is usable, if a little long

[PBKDF2-SHA1 hashing](http://crackstation.net/hashing-security.htm#properhashing) gives

     UserName=1000:153JkeeGAqtG2UsHX57RBqm3O0DIkXhF:31BBDlQrUqqeyaMo/ikCJAXRC4fFXf82

which in my opinion is starting to get too long to be usable.

Is there an algorithm that gives a relatively short one way hash but remains secure / non--reversible?