用RNGCryptoServiceProvider获取随机数

 public string GetRan(int NumSides)
    {
        byte[] randomNumber = new byte[NumSides];
        Gen.GetBytes(randomNumber);
        int rand = Convert.ToInt32(randomNumber[0]);
        StringBuilder sb = new StringBuilder();
        foreach (byte by in randomNumber)
        {
            sb.Append(Convert.ToInt32(by) % NumSides + 1);
        }
        return sb.ToString();
    }