Regex for strong password in ASP.net

Question

I need to check for a password containing 3 of the following 4:

Lowercase letter
Uppercase letter
Numeric character
Special characters (like %, $, #, ...)

The length of the password has to be between 6 and 20 characters. I currently have this:

public void ChangePassword(string password) { Regex regex1 = new Regex("^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z]){6,20}$"); Regex regex2 = new Regex("^(?=.*[0-9])(?=.*[a-z])(?=.*?[#?!@$%^&*-]){6,20}$"); Regex regex3 = new Regex("^(?=.*[0-9])(?=.*[A-Z])(?=.*?[#?!@$%^&*-]){6,20}$"); Regex regex4 = new Regex("^(?=.*[a-z])(?=.*[A-Z])(?=.*?[#?!@$%^&*-]){6,20}$"); Regex regex5 = new Regex("^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*?[#?!@$%^&*-]){6,20}$"); Match match1 = regex1.Match(password); Match match2 = regex2.Match(password); Match match3 = regex3.Match(password); Match match4 = regex4.Match(password); Match match5 = regex5.Match(password); if (match1.Success || match2.Success || match3.Success || match4.Success || match5.Success) { Password = password; } else { throw new PasswordNotGoodException(); } }

However, this doesn't match anything at all. It's for a school project, so I really could use some help.

Possible duplicate of stackoverflow.com/questions/5142103/… — Sean Duggan
– Sean Duggan, Commented Mar 6, 2014 at 18:14

Habib · Accepted Answer · 2014-03-06 18:20:40Z

Instead of REGEX you can use:

string password = "aA1%"; HashSet<char> specialCharacters = new HashSet<char>() { '%', '$', '#' }; if (password.Any(char.IsLower) && //Lower case password.Any(char.IsUpper) && password.Any(char.IsDigit) && password.Any(specialCharacters.Contains)) { //valid password }

Much simpler and clean.

EDIT:

If you need at least 3 out of these 4 conditions to be true you can do:

int conditionsCount = 0; if (password.Any(char.IsLower)) conditionsCount++; if (password.Any(char.IsUpper)) conditionsCount++; if (password.Any(char.IsDigit)) conditionsCount++; if (password.Any(specialCharacters.Contains)) conditionsCount++; if (conditionsCount >= 3) { //valid password }

you are doing all four in && where as OP needed only 3 out of 4 :-)
@SabujHassan, hmm I missed that part, but I guess the OP can fix that logic, my point is Regex is probably an overkill for that.

Toto · Accepted Answer · 2014-03-06 18:14:44Z

The last repetition is wrong here:

Regex regex1 = new Regex("^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z]){6,20}$");

do instead:

Regex regex1 = new Regex("^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z]).{6,20}$"); // notice the dot here ___^

And it's the same for all your regex.

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