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Authenticate password with regular expressions.

Posted on 2014-01-17
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Last Modified: 2014-01-28
I am looking for a way to authenticate a password in C# with regular expressions rather than one big nested set of conditions.

The requirements are,

password has to be at least 6 characters long,
password has to contain a combination of upper / lower case letters (or) password has to contain a punctuation symbol from a given set.

Any ideas/
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Question by:Blowfelt82
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3 Comments
 
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by:Surrano
ID: 39788170
1. Length is easier to check with length than with regex but the simplest regex to match this is (......) (note that there are no ^ nor $ so it can be of any length)

2. Upper-lowercase or puctuation should be piece of cake, e.g.: ([A-Z].*[a-z]|[a-z].*[A-Z]|[-.,;/?])
The only pitfall to watch out for is that a dash must come as first or last of a bracketed set (preferably first)

3. If you wish to combine the two into a single regex, though, it gets much more complicated than it'd worth doing.
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Accepted Solution

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ozo earned 500 total points
ID: 39788506
(?=.{6})((?=.*[A-Z])(?=.*[a-z])|.*[a given set])
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Expert Comment

by:Derek Jensen
ID: 39789909
Why not just make them all required? This can only make for a more secure password, regardless of how much I hate required symbols in passwords. ;-)

(?=.{6,12})((?=.*[A-Z])(?=.*[a-z])(?=.*[sym. char set]))

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I also added a max length to the passwd, in case there's some kind of datatype restriction or something, but passwords should be stored encrypted anyway, so this shouldn't be an issue. :-)
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