Strong password regex [duplicate]

Solution 1:

Doesn't sound like a task particularly suited for Regex, since you want to test multiple conditions simultaneously. (You could use multiple regexes, but then normal C# with LINQ is a nicer way to test it.) Try the following function:

public static bool IsStrongPassword(string password)
{
    // Minimum and Maximum Length of field - 6 to 12 Characters
    if (password.Length < 6 || password.Length > 12)
        return false;

    // Special Characters - Not Allowed
    // Spaces - Not Allowed
    if (!(password.All(c => char.IsLetter(c) || char.IsDigit(c))))  
        return false;

    // Numeric Character - At least one character
    if (!password.Any(c => char.IsDigit(c)))
        return false;

    // At least one Capital Letter
    if (!password.Any(c => char.IsUpper(c)))
        return false;

    // Repetitive Characters - Allowed only two repetitive characters
    var repeatCount = 0;
    var lastChar = '\0';
    foreach(var c in password)
    {
        if (c == lastChar)
            repeatCount++;
        else
            repeatCount = 0;
        if (repeatCount == 2)
            return false;
        lastChar = c;
    }

    return true;
}

Make sure you import System.Linq of course, and you're set to go.

Solution 2:

^(?=.*[A-Z])(?=.*\d)(?!.*(.)\1\1)[a-zA-Z0-9@]{6,12}$

• Special Characters - Not Allowed
• Spaces - Not Allowed
• Minimum and Maximum Length of field - 6 to 12 Characters
  Met by [a-zA-Z0-9@]{6,12}
• Numeric Character - At least one character
  Met by positive lookahead (?=.*\d)
• At least one Capital Letter
  Met by positive lookahead (?=.*[A-Z])
• Repetitive Characters - Allowed only two repetitive characters
  I am not sure what you mean by this. The negative lookahead (?!.*(.)\1\1) makes sure that no character is allowed to appear more than two times in a row. Substring aa is okay, aaa is not.
  Make it (?!.*(.+)\1\1) to reject repeated substrings of length more than one (like ababab) or add .* before \1 to reject non-continuous repeated appearances too.

Solution 3:

You can search the regex library