//Written by Paul Seal. Licensed under MIT. Free for private and commercial uses.

​

using System;

using System.Text.RegularExpressions;

using System.Text;

public class Program

{

    public static void Main()

    {

        const int MAXIMUM_PASSWORD_ATTEMPTS = 10000;

        bool includeLowercase = true;

        bool includeUppercase = true;

        bool includeNumeric = true;

        bool includeSpecial = false;

        int lengthOfPassword  = 16;

        PasswordGeneratorSettings settings = new PasswordGeneratorSettings(includeLowercase, includeUppercase, includeNumeric, includeSpecial, lengthOfPassword);

        string password;

        if (!settings.IsValidLength())

        {

            password = settings.LengthErrorMessage();

        }

        else

        {

            int passwordAttempts = 0;

            do

            {

                password = PasswordGenerator.GeneratePassword(settings);

                passwordAttempts++;

            }

            while (passwordAttempts < MAXIMUM_PASSWORD_ATTEMPTS && !PasswordGenerator.PasswordIsValid(settings, password));

            password = PasswordGenerator.PasswordIsValid(settings, password) ? password : "Try again";

        }

        Console.WriteLine(password);

    }

}

​

public class PasswordGeneratorSettings

{

    const string LOWERCASE_CHARACTERS = "abcdefghijklmnopqrstuvwxyz";

    const string UPPERCASE_CHARACTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    const string NUMERIC_CHARACTERS = "0123456789";

    const string SPECIAL_CHARACTERS = @"!#$%&*@\";

    const int PASSWORD_LENGTH_MIN = 8;

    const int PASSWORD_LENGTH_MAX = 128;

    public bool IncludeLowercase {get; set; }

    public bool IncludeUppercase { get; set; }

    public bool IncludeNumbers { get; set; }

    public bool IncludeSpecial { get; set; }

    public int PasswordLength { get; set; }

    public string CharacterSet { get; set; }

    public int MaximumAttempts { get; set; }

    public PasswordGeneratorSettings(bool includeLowercase, bool includeUppercase, bool includeNumbers, bool includeSpecial, int passwordLength)

    {

        IncludeLowercase = includeLowercase;

        IncludeUppercase = includeUppercase;

        IncludeNumbers = includeNumbers;

        IncludeSpecial = includeSpecial;

        PasswordLength = passwordLength;

        StringBuilder characterSet = new StringBuilder();

        if (includeLowercase)

        {

            characterSet.Append(LOWERCASE_CHARACTERS);

        }

        if (includeUppercase)

        {

            characterSet.Append(UPPERCASE_CHARACTERS);

        }

        if (includeNumbers)

        {

            characterSet.Append(NUMERIC_CHARACTERS);

        }

        if (includeSpecial)

        {

            characterSet.Append(SPECIAL_CHARACTERS);

        }

        CharacterSet = characterSet.ToString();

    }

    public bool IsValidLength()

    {

        return PasswordLength >= PASSWORD_LENGTH_MIN && PasswordLength <= PASSWORD_LENGTH_MAX;

    }

    public string LengthErrorMessage()

    {

        return string.Format("Password length must be between {0} and {1} characters", PASSWORD_LENGTH_MIN, PASSWORD_LENGTH_MAX);

    }

}

​

​

public static class PasswordGenerator

{

    /// <summary>

    /// Generates a random password based on the rules passed in the settings parameter

    /// </summary>

    /// <param name="settings">Password generator settings object</param>

    /// <returns>Password or try again</returns>

    public static string GeneratePassword(PasswordGeneratorSettings settings)

    {

        const int MAXIMUM_IDENTICAL_CONSECUTIVE_CHARS = 2;

        char[] password = new char[settings.PasswordLength];

        int characterSetLength = settings.CharacterSet.Length;

        System.Random random = new System.Random();

        for (int characterPosition = 0; characterPosition < settings.PasswordLength; characterPosition++)

        {

            password[characterPosition] = settings.CharacterSet[random.Next(characterSetLength - 1)];

            bool moreThanTwoIdenticalInARow =

                characterPosition > MAXIMUM_IDENTICAL_CONSECUTIVE_CHARS

                && password[characterPosition] == password[characterPosition - 1]

                && password[characterPosition - 1] == password[characterPosition - 2];

            if (moreThanTwoIdenticalInARow)

            {

                characterPosition--;

            }

        }

        return string.Join(null, password);

    }

    /// <summary>

    /// When you give it a password and some settings, it validates the password against the settings.

    /// </summary>

    /// <param name="settings">Password settings</param>

    /// <param name="password">Password to test</param>

    /// <returns>True or False to say if the password is valid or not</returns>

    public static bool PasswordIsValid(PasswordGeneratorSettings settings, string password)

    {

        const string REGEX_LOWERCASE = @"[a-z]";

        const string REGEX_UPPERCASE = @"[A-Z]";

        const string REGEX_NUMERIC = @"[\d]";

        const string REGEX_SPECIAL = @"([!#$%&*@\\])+";

        bool lowerCaseIsValid = !settings.IncludeLowercase || (settings.IncludeLowercase && Regex.IsMatch(password, REGEX_LOWERCASE));

        bool upperCaseIsValid = !settings.IncludeUppercase || (settings.IncludeUppercase && Regex.IsMatch(password, REGEX_UPPERCASE));

        bool numericIsValid = !settings.IncludeNumbers || (settings.IncludeNumbers && Regex.IsMatch(password, REGEX_NUMERIC));

        bool symbolsAreValid = !settings.IncludeSpecial || (settings.IncludeSpecial && Regex.IsMatch(password, REGEX_SPECIAL));

        return lowerCaseIsValid && upperCaseIsValid && numericIsValid && symbolsAreValid;

    }

}

​