#region 获取随机字符串
//digit 最终返回的字符串的长度
        public static string BuildCode(int digit)
        {
            StringBuilder resultCode = new StringBuilder();
            Random ran = new Random(GetRandomSeed());
            for (int i = 0; i < digit; i++)
            {
                resultCode.Append(("0123456789").Substring(ran.Next(0, 10), 1));
            }
            string resultCode1 = resultCode.ToString();
            return resultCode1;
        }
        static int GetRandomSeed()
        {
            byte[] bytes = new byte[4];
            System.Security.Cryptography.RNGCryptoServiceProvider rng = new System.Security.Cryptography.RNGCryptoServiceProvider();
            rng.GetBytes(bytes);
            return BitConverter.ToInt32(bytes, 0);
        }
        #endregion
原文:http://www.cnblogs.com/zxk3113/p/5231947.html