vb.net function to check new password's significant uniqueness

One of our new password strength criteria is for the new password to be uniquely different from the old one.  For example I'm trying to prevent things like:
   Old Password: TestPass01
   New Password: TestPass02

I've been looking online all day.  I guess I'm just not using the correct key words in my searches.
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Steve SiricaSenior Web Application EngineerAsked:
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PaulHewsCommented:
If you are hashing the password, then you can't.  You can only tell if they are identical, which is the point of hashing.

If you are storing the password, then you should consider storing the hash instead.

Assuming you are storing the password, you could do use a longest common sub-string type of algorithm and prevent instances where the common substring is almost equal to the length of the new password.

http://en.wikibooks.org/wiki/Algorithm_Implementation/Strings/Longest_common_substring
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Steve SiricaSenior Web Application EngineerAuthor Commented:
I can make that work.  Thanks.
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