using System;

using System.Text;

using System.Security.Cryptography;

public class Program

{

    public static void Main()

    {

        var password = RandomString(15);

        Console.WriteLine("value: " + password);

    }

    static string RandomString(int length)

    {

        const string valid = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";

        StringBuilder res = new StringBuilder();

        using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())

        {

            byte[] uintBuffer = new byte[sizeof(uint)];

            while (length-- > 0)

            {

                rng.GetBytes(uintBuffer);

                uint num = BitConverter.ToUInt32(uintBuffer, 0);

                res.Append(valid[(int)(num % (uint)valid.Length)]);

            }

        }

        return res.ToString();

    }

}