转载 URL短地址压缩算法

        /// <summary>
        /// 生成salt
        /// </summary>
        /// <returns></returns>
        public static string GenerateSalt()
        {
            byte[] data = new byte[0x10];
            new RNGCryptoServiceProvider().GetBytes(data);
            return Convert.ToBase64String(data);
        }

        public static string[] ShortUrl(string url)
        {
            //可以自定义生成MD5加密字符传前的混合KEY     
            string key = "anech";
            //要使用生成URL的字符     
            string[] chars = new string[]{    
        "a" , "b" , "c" , "d" , "e" , "f" , "g" , "h" ,    
        "i" , "j" , "k" , "l" , "m" , "n" , "o" , "p" ,    
        "q" , "r" , "s" , "t" , "u" , "v" , "w" , "x" ,    
         "y" , "z" , "0" , "1" , "2" , "3" , "4" , "5" ,    
         "6" , "7" , "8" , "9" , "A" , "B" , "C" , "D" ,    
         "E" , "F" , "G" , "H" , "I" , "J" , "K" , "L" ,    
         "M" , "N" , "O" , "P" , "Q" , "R" , "S" , "T" ,    
         "U" , "V" , "W" , "X" , "Y" , "Z"     
     };

            //对传入网址进行MD5加密     
            string hex = MD5(key + url);

            string[] resUrl = new string[4];

            for (int i = 0; i < 4; i++)
            {
                //把加密字符按照8位一组16进制与0x3FFFFFFF进行位与运算     
                int hexint = 0x3FFFFFFF & Convert.ToInt32("0x" + hex.Substring(i * 8, 8), 16);
                string outChars = string.Empty;
                for (int j = 0; j < 6; j++)
                {
                    //把得到的值与0x0000003D进行位与运算，取得字符数组chars索引     
                    int index = 0x0000003D & hexint;
                    //把取得的字符相加     
                    outChars += chars[index];
                    //每次循环按位右移5位     
                    hexint = hexint >> 5;
                }
                //把字符串存入对应索引的输出数组     
                resUrl[i] = outChars;
            }
            return resUrl;
        }

        public static string MD5(String input)
        {
            byte[] res = new MD5CryptoServiceProvider().ComputeHash(Encoding.Default.GetBytes(input));
            return BitConverter.ToString(res).Replace("-", "");
        }