生成中文随机验证码

public static string GetGb2312()
        {
            Encoding gb = Encoding.GetEncoding("gb2312"); //获取GB2312编码页（表）

            object[] bytes = CreateRegionCode(4); //调用函数产生4个随机中文汉字编码

           
            string str = gb.GetString((byte[])Convert.ChangeType(bytes[0], typeof(byte[])));//根据汉字编码的字节数组解码出中文汉字
            str += gb.GetString((byte[])Convert.ChangeType(bytes[1], typeof(byte[])));
            str += gb.GetString((byte[])Convert.ChangeType(bytes[2], typeof(byte[])));
            str += gb.GetString((byte[])Convert.ChangeType(bytes[3], typeof(byte[])));

            return str;
        }

       /* 
       此函数在汉字编码范围内随机创建含两个元素的十六进制字节数组，每个字节数组代表一个汉字，并将 
       四个字节数组存储在object数组中。 
       参数：strlength，代表需要产生的汉字个数 
       */
        public static object[] CreateRegionCode(int strlength)
        {
            //定义一个字符串数组储存汉字编码的组成元素
            string[] rBase = new String[16] { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f" };

            Random rnd = new Random();

            //定义一个object数组用来
            object[] bytes = new object[strlength];

            /*每循环一次产生一个含两个元素的十六进制字节数组，并将其放入bject数组中
            每个汉字有四个区位码组成
            区位码第1位和区位码第2位作为字节数组第一个元素
            区位码第3位和区位码第4位作为字节数组第二个元素
            */
            for (int i = 0; i < strlength; i++)
            {
                //区位码第1位
                int r1 = rnd.Next(11, 14);
                string str_r1 = rBase[r1].Trim();

                //区位码第2位
                rnd = new Random(r1 * unchecked((int)DateTime.Now.Ticks) + i);//更换随机数发生器的 种子避免产生重复值
                int r2;
                if (r1 == 13)
                {
                    r2 = rnd.Next(0, 7);
                }
                else
                {
                    r2 = rnd.Next(0, 16);
                }
                string str_r2 = rBase[r2].Trim();

                //区位码第3位
                rnd = new Random(r2 * unchecked((int)DateTime.Now.Ticks) + i);
                int r3 = rnd.Next(10, 16);
                string str_r3 = rBase[r3].Trim();

                //区位码第4位
                rnd = new Random(r3 * unchecked((int)DateTime.Now.Ticks) + i);
                int r4;
                if (r3 == 10)
                {
                    r4 = rnd.Next(1, 16);
                }
                else if (r3 == 15)
                {
                    r4 = rnd.Next(0, 15);
                }
                else
                {
                    r4 = rnd.Next(0, 16);
                }
                string str_r4 = rBase[r4].Trim();

                //定义两个字节变量存储产生的随机汉字区位码
                byte byte1 = Convert.ToByte(str_r1 + str_r2, 16);
                byte byte2 = Convert.ToByte(str_r3 + str_r4, 16);
                //将两个字节变量存储在字节数组中
                byte[] str_r = new byte[] { byte1, byte2 };

                //将产生的一个汉字的字节数组放入object数组中
                bytes.SetValue(str_r, i);

            }

            return bytes;

        }