Validating password using regex c#

Question

This must be simple and I expect it working in the same way but it's not helping me out.

using System;
using System.Text.RegularExpressions;

I am in a need of password validation regular expression with certain conditions where -

1) It must contain at least a number

2) one upper case letter

3) 8 characters long.

public class Program
{
     public static bool IsValidPassword(string plainText) {
            Regex regex = new Regex(@"^(.{0,7}|[^0-9]*|[^A-Z])$");
            Match match = regex.Match(plainText);
            return match.Success;
}
    public static void Main()
    {
        Console.WriteLine(IsValidPassword("shing"));    //logs 'True' always
    }
}

I've taken regex from this source- Password must be 8 characters including 1 uppercase letter, 1 special character, alphanumeric characters

Issue is that it returns 'True' always and the string that I am sending to method is not valid.

Help me if I am doing something wrong with the regex.

Please play with it here- https://dotnetfiddle.net/lEFYGJ

Answer 1

I recommend you create separate patterns to validate the password:

var input = "P@ssw0rd";

var hasNumber = new Regex(@"[0-9]+");
var hasUpperChar = new Regex(@"[A-Z]+");
var hasMinimum8Chars = new Regex(@".{8,}");

var isValidated = hasNumber.IsMatch(input) && hasUpperChar.IsMatch(input) && hasMinimum8Chars.IsMatch(input);
Console.WriteLine(isValidated);

Answer 2

I have created a simple method to validate all kind of password. You can edit your limit on that. Kindly find the code given below.

private bool ValidatePassword(string password, out string ErrorMessage)
{
    var input = password;
    ErrorMessage = string.Empty;

    if (string.IsNullOrWhiteSpace(input))
    {
        throw new Exception("Password should not be empty");
    }

    var hasNumber = new Regex(@"[0-9]+");
    var hasUpperChar = new Regex(@"[A-Z]+");
    var hasMiniMaxChars = new Regex(@".{8,15}");
    var hasLowerChar = new Regex(@"[a-z]+");
    var hasSymbols = new Regex(@"[!@#$%^&*()_+=\[{\]};:<>|./?,-]");

    if (!hasLowerChar.IsMatch(input))
    {
        ErrorMessage = "Password should contain At least one lower case letter";
        return false;
    }
    else if (!hasUpperChar.IsMatch(input))
    {
        ErrorMessage = "Password should contain At least one upper case letter";
        return false;
    }
    else if (!hasMiniMaxChars.IsMatch(input))
    {
        ErrorMessage = "Password should not be less than or greater than 12 characters";
        return false;
    }
    else if (!hasNumber.IsMatch(input))
    {
        ErrorMessage = "Password should contain At least one numeric value";
        return false;
    }

    else if (!hasSymbols.IsMatch(input))
    {
        ErrorMessage = "Password should contain At least one special case characters";
        return false;
    }
    else
    {
        return true;
    }
}

Answer 3

there is problem with you regular expression

Regex regex = new Regex(@"^(.{0,7}|[^0-9]*|[^A-Z])$");

you applied character | which means either or.

form wiki

| -The choice (also known as alternation or set union) operator matches either the expression before or the expression after the operator. For example, abc|def matches "abc" or "def".

which means that in your regular expression it either matches .{0,7} part or [^0-9]*|[^A-Z] - that is why its returning true to you in any case.

---

You can use this regex:

^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[#?!@$%^&*-]).{8,}$

This regex will enforce these rules: • At least one upper case english letter • At least one lower case english letter • At least one digit • At least one special character • Minimum 8 in length

refered from : Regex for Password Must be contain at least 8 characters, least 1 number and both lower and uppercase letters and special characters

Answer 4

Pattern satisfy, these below criteria

1. Password of Length 8
2. Requires at least 1 Unique Char.
3. Requires 1 Digit
4. Requires 1 Lower Case character
5. Requires 1 Upper Case character
6. Requires 1 Special Character

^(?!.([A-Za-z0-9])\1{1})(?=.?[A-Z])(?=.?[a-z])(?=.?[0-9])(?=.?[#?!@$%^&-]).{8,}$

For example:- It satisfies password like:- Admin@123

Answer 5

Ok, Found out to be a change in expression. A good explanation by @mmdemirbas here-

Password must be 8 characters including 1 uppercase letter, 1 special character, alphanumeric characters

(                   # Start of group
    (?=.*\d)        #   must contain at least one digit
    (?=.*[A-Z])     #   must contain at least one uppercase character
    (?=.*\W)        #   must contain at least one special symbol
       .            #     match anything with previous condition checking
         {8,8}      #        length at least 8 characters and also maximum of 8
)                   # End of group

My end expression now is-

((?=.*\d)(?=.*[A-Z]).{8,50})

Thanks everyone for stopping by.

working here- https://dotnetfiddle.net/lEFYGJ

Answer 6

You can use this,

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[^\da-zA-Z]).{8,15}$