using System;

using System.Linq;

using System.Security.Cryptography;

public class Program

{

    private static readonly char[] AcceptableCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890!@#$%^&*()_-+=[{]};:<>|./?".ToCharArray();

    public static void Main()

    {

        // Option 1, RandomNumberGenerator built in static string generation

        ReadOnlySpan<char> charSpan = AcceptableCharacters;

        var secure = RandomNumberGenerator.GetString(charSpan, 20);

        Console.WriteLine($"Super Top Secret Temporary Password: {secure}");

        // Option 2, RandomNumberGenerator random bytes

        string securePassword = PasswordGenerator.GenerateSecurePassword(12, 4);

        Console.WriteLine("Generated Secure Password: " + securePassword);

    }

}

​

public class PasswordGenerator

{

    private static readonly char[] AlphanumericCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890".ToCharArray();

    private static readonly char[] NonAlphanumericCharacters = "!@#$%^&*()_-+=[{]};:<>|./?".ToCharArray();

​

    public static string GenerateSecurePassword(int length, int numberOfNonAlphanumericCharacters)

    {

        if (length < 1 || numberOfNonAlphanumericCharacters > length || numberOfNonAlphanumericCharacters < 0)

        {

            throw new ArgumentException("Invalid length or number of non-alphanumeric characters specified.");

        }

​

        char[] password = new char[length];

        int[] selectedIndexes = Enumerable.Range(0, length).ToArray();

​

        using (RandomNumberGenerator rng = RandomNumberGenerator.Create())

        {

            byte[] randomBytes = new byte[length];

            rng.GetBytes(randomBytes);

            selectedIndexes = selectedIndexes.OrderBy(x => randomBytes[x % randomBytes.Length]).ToArray();

​

            for (int i = 0; i < numberOfNonAlphanumericCharacters; i++)

            {

                password[selectedIndexes[i]] = NonAlphanumericCharacters[randomBytes[i % randomBytes.Length] % NonAlphanumericCharacters.Length];

            }

​

            for (int i = numberOfNonAlphanumericCharacters; i < length; i++)

            {

                password[selectedIndexes[i]] = AlphanumericCharacters[randomBytes[i % randomBytes.Length] % AlphanumericCharacters.Length];

            }

        }

​

        return new string(password);

    }

}