using System;

using System.Security.Cryptography;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(GenerateRandomToken());

    }

​

    public static string GenerateRandomToken(int tokenSize = 10)

    {

        string chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";

        using (var crypto = new RNGCryptoServiceProvider())

        {

            var data = new byte[tokenSize];

            byte[] smallBuffer = null;

            int maxRandom = byte.MaxValue - ((byte.MaxValue + 1) % chars.Length);

            crypto.GetBytes(data);

​

            var result = new char[tokenSize];

​

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

            {

                byte v = data[i];

                while (v > maxRandom)

                {

                    if (smallBuffer == null)

                        smallBuffer = new byte[1];

​

                    crypto.GetBytes(smallBuffer);

                    v = smallBuffer[0];

                }

                result[i] = chars[v % chars.Length];

            }

            return new string(result);

        }

    }

}