How to validate password in alphanumeric format with one numeric and one special character at minimum.in ASP.NET with C#?

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I want to validate password in Alphanumeric Format with one numeric and one special character at minimum.in asp.net with c#. I am able to validate the alphanumeric format but i need to validate

Alphanumeric with one numeric and one special character at minimum. Code for the same is updated below

What I have tried:

#region IsAlphaNumeric
      public static bool IsAlphaNumeric(string inputAlphabet)
      {
         const string expression = @"^[A-Za-z0-9]+$";

          Regex regex = new Regex(expression);
          return regex.IsMatch(inputAlphabet);
      }

      #endregion

Posted 24-Oct-21 22:11pm

ranio

Updated 24-Oct-21 22:42pm

v2

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Richard Deeming · Answer 1 · 2021-10-24T22:37:00

Solution 1

Presumably at least one numeric and at least one special character?

Also, if you're allowing special characters, it's not going to be "alphanumeric".

This pattern validates:

at least one upper-case letter;
at least one lower-case letter;
at least one number;
at least one "special character"; and
minimum length of 10;

RegEx

(?=.*[A-Z])(?=.*[a-z])(?=.*\d)(?=.*[^\w\s])^.{10,}$

Zero-Width Positive Lookahead Assertions | Microsoft Docs[^]

Posted 24-Oct-21 22:37pm

Richard Deeming

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ranio 25-Oct-21 5:47am

will below Regex Pattern works for the Password to contain at least one number;
at least one "special character and length of 7
(?=.*)(?=.*)(?=.*\d)(?=.*[^\w\s])^.{7,}$

Richard Deeming 25-Oct-21 5:48am

Take the two (?=.*) groups out, since they don't do anything. Otherwise, it should work as you describe.

OriginalGriff · Answer 2 · 2021-10-24T22:42:00

A regex is a poor tool for password validation - it's a text processor not a semantic analysis tool.
If you want to count items, then use multiple regexes:

[A-Za-Z]

\d

[!"£$%^&*()-_=+]

And use the Regex.Matches[^] method to return a MatchCollection for each. You can then use it's Count property to tell you how many there are: 0 is bad, non-zero in all of them is OK.

But ... enforcing password strength is normally a poor idea: it reduces security as it either encourages people to write it down, or to use the same password for all logins.
Why enforced password complexity is worse for security (and what to do about it)[^]