1、DES加密字串及檔案等

如果想可逆的演算法，這種方式一般不錯，只要結合動態金鑰，就可以做出強度比較高的加密應用了。

         #region DES對稱加密解密

        public const string DEFAULT_ENCRYPT_KEY = "12345678";

        /// <summary>
        /// 使用預設加密
        /// </summary>
        /// <param name="strText"></param>
        /// <returns></returns>
        public static string DesEncrypt(string strText)
        {
            try
            {
                return DesEncrypt(strText, DEFAULT_ENCRYPT_KEY);
            }
            catch
            {
                return "";
            }
        }

        /// <summary>
        /// 使用預設解密
        /// </summary>
        /// <param name="strText"></param>
        /// <returns></returns>
        public static string DesDecrypt(string strText)
        {
            try
            {
                return DesDecrypt(strText, DEFAULT_ENCRYPT_KEY);
            }
            catch
            {
                return "";
            }
        }

        /// <summary>
        /// Encrypt the string
        /// Attention:key must be 8 bits
        /// </summary>
        /// <param name="strText">string</param>
        /// <param name="strEncrKey">key</param>
        /// <returns></returns>
        public static string DesEncrypt(string strText, string strEncrKey)
        {
            byte[] byKey = null;
            byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

            byKey = Encoding.UTF8.GetBytes(strEncrKey.Substring(0, 8));
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();
            byte[] inputByteArray = Encoding.UTF8.GetBytes(strText);
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(byKey, IV), CryptoStreamMode.Write);
            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();
            return Convert.ToBase64String(ms.ToArray());
        }

        /// <summary>
        /// Decrypt string
        /// Attention:key must be 8 bits
        /// </summary>
        /// <param name="strText">Decrypt string</param>
        /// <param name="sDecrKey">key</param>
        /// <returns>output string</returns>
        public static string DesDecrypt(string strText, string sDecrKey)
        {
            byte[] byKey = null;
            byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };
            byte[] inputByteArray = new Byte[strText.Length];

            byKey = Encoding.UTF8.GetBytes(sDecrKey.Substring(0, 8));
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();
            inputByteArray = Convert.FromBase64String(strText);
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(byKey, IV), CryptoStreamMode.Write);
            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();
            Encoding encoding = new UTF8Encoding();
            return encoding.GetString(ms.ToArray());
        }

        /// <summary>
        /// Encrypt files
        /// Attention:key must be 8 bits
        /// </summary>
        /// <param name="m_InFilePath">Encrypt file path</param>
        /// <param name="m_OutFilePath">output file</param>
        /// <param name="strEncrKey">key</param>
        public static void DesEncrypt(string m_InFilePath, string m_OutFilePath, string strEncrKey)
        {
            byte[] byKey = null;
            byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

            byKey = Encoding.UTF8.GetBytes(strEncrKey.Substring(0, 8));
            FileStream fin = new FileStream(m_InFilePath, FileMode.Open, FileAccess.Read);
            FileStream fout = new FileStream(m_OutFilePath, FileMode.OpenOrCreate, FileAccess.Write);
            fout.SetLength(0);
            //Create variables to help with read and write.
            byte[] bin = new byte[100]; //This is intermediate storage for the encryption.
            long rdlen = 0; //This is the total number of bytes written.
            long totlen = fin.Length; //This is the total length of the input file.
            int len; //This is the number of bytes to be written at a time.

            DES des = new DESCryptoServiceProvider();
            CryptoStream encStream = new CryptoStream(fout, des.CreateEncryptor(byKey, IV), CryptoStreamMode.Write);

            //Read from the input file, then encrypt and write to the output file.
            while (rdlen < totlen)
            {
                len = fin.Read(bin, 0, 100);
                encStream.Write(bin, 0, len);
                rdlen = rdlen + len;
            }
            encStream.Close();
            fout.Close();
            fin.Close();
        }

        /// <summary>
        /// Decrypt files
        /// Attention:key must be 8 bits
        /// </summary>
        /// <param name="m_InFilePath">Decrypt filepath</param>
        /// <param name="m_OutFilePath">output filepath</param>
        /// <param name="sDecrKey">key</param>
        public static void DesDecrypt(string m_InFilePath, string m_OutFilePath, string sDecrKey)
        {
            byte[] byKey = null;
            byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

            byKey = Encoding.UTF8.GetBytes(sDecrKey.Substring(0, 8));
            FileStream fin = new FileStream(m_InFilePath, FileMode.Open, FileAccess.Read);
            FileStream fout = new FileStream(m_OutFilePath, FileMode.OpenOrCreate, FileAccess.Write);
            fout.SetLength(0);
            //Create variables to help with read and write.
            byte[] bin = new byte[100]; //This is intermediate storage for the encryption.
            long rdlen = 0; //This is the total number of bytes written.
            long totlen = fin.Length; //This is the total length of the input file.
            int len; //This is the number of bytes to be written at a time.

            DES des = new DESCryptoServiceProvider();
            CryptoStream encStream = new CryptoStream(fout, des.CreateDecryptor(byKey, IV), CryptoStreamMode.Write);

            //Read from the input file, then encrypt and write to the output file.
            while (rdlen < totlen)
            {
                len = fin.Read(bin, 0, 100);
                encStream.Write(bin, 0, len);
                rdlen = rdlen + len;
            }
            encStream.Close();
            fout.Close();
            fin.Close();
        }
        #endregion

2、 對稱加密演算法AES RijndaelManaged加密解密

         #region 對稱加密演算法AES RijndaelManaged加密解密

        private static readonly string Default_AES_Key = "@#kim123";
        private static byte[] Keys = { 0x41, 0x72, 0x65, 0x79, 0x6F, 0x75, 0x6D, 0x79,
                                             0x53,0x6E, 0x6F, 0x77, 0x6D, 0x61, 0x6E, 0x3F };

        /// <summary>
        /// 對稱加密演算法AES RijndaelManaged加密(RijndaelManaged（AES）演算法是塊式加密演算法)
        /// </summary>
        /// <param name="encryptString">待加密字串</param>
        /// <returns>加密結果字串</returns>
        public static string AES_Encrypt(string encryptString)
        {
            return AES_Encrypt(encryptString, Default_AES_Key);
        }

        /// <summary>
        /// 對稱加密演算法AES RijndaelManaged加密(RijndaelManaged（AES）演算法是塊式加密演算法)
        /// </summary>
        /// <param name="encryptString">待加密字串</param>
        /// <param name="encryptKey">加密金鑰，須半形字元</param>
        /// <returns>加密結果字串</returns>
        public static string AES_Encrypt(string encryptString, string encryptKey)
        {
            encryptKey = GetSubString(encryptKey, 32, "");
            encryptKey = encryptKey.PadRight(32, ' ');

            RijndaelManaged rijndaelProvider = new RijndaelManaged();
            rijndaelProvider.Key = Encoding.UTF8.GetBytes(encryptKey.Substring(0, 32));
            rijndaelProvider.IV = Keys;
            ICryptoTransform rijndaelEncrypt = rijndaelProvider.CreateEncryptor();

            byte[] inputData = Encoding.UTF8.GetBytes(encryptString);
            byte[] encryptedData = rijndaelEncrypt.TransformFinalBlock(inputData, 0, inputData.Length);

            return Convert.ToBase64String(encryptedData);
        }

        /// <summary>
        /// 對稱加密演算法AES RijndaelManaged解密字串
        /// </summary>
        /// <param name="decryptString">待解密的字串</param>
        /// <returns>解密成功返回解密後的字串,失敗返源串</returns>
        public static string AES_Decrypt(string decryptString)
        {
            return AES_Decrypt(decryptString, Default_AES_Key);
        }

        /// <summary>
        /// 對稱加密演算法AES RijndaelManaged解密字串
        /// </summary>
        /// <param name="decryptString">待解密的字串</param>
        /// <param name="decryptKey">解密金鑰,和加密金鑰相同</param>
        /// <returns>解密成功返回解密後的字串,失敗返回空</returns>
        public static string AES_Decrypt(string decryptString, string decryptKey)
        {
            try
            {
                decryptKey = GetSubString(decryptKey, 32, "");
                decryptKey = decryptKey.PadRight(32, ' ');

                RijndaelManaged rijndaelProvider = new RijndaelManaged();
                rijndaelProvider.Key = Encoding.UTF8.GetBytes(decryptKey);
                rijndaelProvider.IV = Keys;
                ICryptoTransform rijndaelDecrypt = rijndaelProvider.CreateDecryptor();

                byte[] inputData = Convert.FromBase64String(decryptString);
                byte[] decryptedData = rijndaelDecrypt.TransformFinalBlock(inputData, 0, inputData.Length);

                return Encoding.UTF8.GetString(decryptedData);
            }
            catch
            {
                return string.Empty;
            }
        }

        /// <summary>
        /// 按位元組長度(按位元組,一個漢字為2個位元組)取得某字串的一部分
        /// </summary>
        /// <param name="sourceString">源字串</param>
        /// <param name="length">所取字串位元組長度</param>
        /// <param name="tailString">附加字串(當字串不夠長時，尾部所新增的字串，一般為"...")</param>
        /// <returns>某字串的一部分</returns>
        private static string GetSubString(string sourceString, int length, string tailString)
        {
            return GetSubString(sourceString, 0, length, tailString);
        }

        /// <summary>
        /// 按位元組長度(按位元組,一個漢字為2個位元組)取得某字串的一部分
        /// </summary>
        /// <param name="sourceString">源字串</param>
        /// <param name="startIndex">索引位置，以0開始</param>
        /// <param name="length">所取字串位元組長度</param>
        /// <param name="tailString">附加字串(當字串不夠長時，尾部所新增的字串，一般為"...")</param>
        /// <returns>某字串的一部分</returns>
        private static string GetSubString(string sourceString, int startIndex, int length, string tailString)
        {
            string myResult = sourceString;

            //當是日文或韓文時(注:中文的範圍:\u4e00 - \u9fa5, 日文在\u0800 - \u4e00, 韓文為\xAC00-\xD7A3)
            if (System.Text.RegularExpressions.Regex.IsMatch(sourceString, "[\u0800-\u4e00]+") ||
                System.Text.RegularExpressions.Regex.IsMatch(sourceString, "[\xAC00-\xD7A3]+"))
            {
                //當擷取的起始位置超出欄位串長度時
                if (startIndex >= sourceString.Length)
                {
                    return string.Empty;
                }
                else
                {
                    return sourceString.Substring(startIndex,
                                                   ((length + startIndex) > sourceString.Length) ? (sourceString.Length - startIndex) : length);
                }
            }

            //中文字元，如"中國人民abcd123"
            if (length <= 0)
            {
                return string.Empty;
            }
            byte[] bytesSource = Encoding.Default.GetBytes(sourceString);

            //當字串長度大於起始位置
            if (bytesSource.Length > startIndex)
            {
                int endIndex = bytesSource.Length;

                //當要擷取的長度在字串的有效長度範圍內
                if (bytesSource.Length > (startIndex + length))
                {
                    endIndex = length + startIndex;
                }
                else
                {   //當不在有效範圍內時,只取到字串的結尾
                    length = bytesSource.Length - startIndex;
                    tailString = "";
                }

                int[] anResultFlag = new int[length];
                int nFlag = 0;
                //位元組大於127為雙位元組字元
                for (int i = startIndex; i < endIndex; i++)
                {
                    if (bytesSource[i] > 127)
                    {
                        nFlag++;
                        if (nFlag == 3)
                        {
                            nFlag = 1;
                        }
                    }
                    else
                    {
                        nFlag = 0;
                    }
                    anResultFlag[i] = nFlag;
                }
                //最後一個位元組為雙位元組字元的一半
                if ((bytesSource[endIndex - 1] > 127) && (anResultFlag[length - 1] == 1))
                {
                    length = length + 1;
                }

                byte[] bsResult = new byte[length];
                Array.Copy(bytesSource, startIndex, bsResult, 0, length);
                myResult = Encoding.Default.GetString(bsResult);
                myResult = myResult + tailString;

                return myResult;
            }

            return string.Empty;

        }

        /// <summary>
        /// 加密檔案流
        /// </summary>
        /// <param name="fs"></param>
        /// <returns></returns>
        public static CryptoStream AES_EncryptStrream(FileStream fs, string decryptKey)
        {
            decryptKey = GetSubString(decryptKey, 32, "");
            decryptKey = decryptKey.PadRight(32, ' ');

            RijndaelManaged rijndaelProvider = new RijndaelManaged();
            rijndaelProvider.Key = Encoding.UTF8.GetBytes(decryptKey);
            rijndaelProvider.IV = Keys;

            ICryptoTransform encrypto = rijndaelProvider.CreateEncryptor();
            CryptoStream cytptostreamEncr = new CryptoStream(fs, encrypto, CryptoStreamMode.Write);
            return cytptostreamEncr;
        }

        /// <summary>
        /// 解密檔案流
        /// </summary>
        /// <param name="fs"></param>
        /// <returns></returns>
        public static CryptoStream AES_DecryptStream(FileStream fs, string decryptKey)
        {
            decryptKey = GetSubString(decryptKey, 32, "");
            decryptKey = decryptKey.PadRight(32, ' ');

            RijndaelManaged rijndaelProvider = new RijndaelManaged();
            rijndaelProvider.Key = Encoding.UTF8.GetBytes(decryptKey);
            rijndaelProvider.IV = Keys;
            ICryptoTransform Decrypto = rijndaelProvider.CreateDecryptor();
            CryptoStream cytptostreamDecr = new CryptoStream(fs, Decrypto, CryptoStreamMode.Read);
            return cytptostreamDecr;
        }

        /// <summary>
        /// 對指定檔案加密
        /// </summary>
        /// <param name="InputFile"></param>
        /// <param name="OutputFile"></param>
        /// <returns></returns>
        public static bool AES_EncryptFile(string InputFile, string OutputFile)
        {
            try
            {
                string decryptKey = "www.iqidi.com";

                FileStream fr = new FileStream(InputFile, FileMode.Open);
                FileStream fren = new FileStream(OutputFile, FileMode.Create);
                CryptoStream Enfr = AES_EncryptStrream(fren, decryptKey);
                byte[] bytearrayinput = new byte[fr.Length];
                fr.Read(bytearrayinput, 0, bytearrayinput.Length);
                Enfr.Write(bytearrayinput, 0, bytearrayinput.Length);
                Enfr.Close();
                fr.Close();
                fren.Close();
            }
            catch
            {
                //檔案異常
                return false;
            }
            return true;
        }

        /// <summary>
        /// 對指定的檔案解壓縮
        /// </summary>
        /// <param name="InputFile"></param>
        /// <param name="OutputFile"></param>
        /// <returns></returns>
        public static bool AES_DecryptFile(string InputFile, string OutputFile)
        {
            try
            {
                string decryptKey = "www.iqidi.com";
                FileStream fr = new FileStream(InputFile, FileMode.Open);
                FileStream frde = new FileStream(OutputFile, FileMode.Create);
                CryptoStream Defr = AES_DecryptStream(fr, decryptKey);
                byte[] bytearrayoutput = new byte[1024];
                int m_count = 0;

                do
                {
                    m_count = Defr.Read(bytearrayoutput, 0, bytearrayoutput.Length);
                    frde.Write(bytearrayoutput, 0, m_count);
                    if (m_count < bytearrayoutput.Length)
                        break;
                } while (true);

                Defr.Close();
                fr.Close();
                frde.Close();
            }
            catch
            {
                //檔案異常
                return false;
            }
            return true;
        }
       
        #endregion

3、  Base64加密解密演算法

         #region Base64加密解密

        /// <summary>
        /// Base64是一種使用64基的位置計數法。它使用2的最大次方來代表僅可列印的ASCII 字元。
        /// 這使它可用來作為電子郵件的傳輸編碼。在Base64中的變數使用字元A-Z、a-z和0-9 ，
        /// 這樣共有62個字元，用來作為開始的64個數字，最後兩個用來作為數字的符號在不同的
        /// 系統中而不同。
        /// Base64加密
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        public static string Base64Encrypt(string str)
        {
            byte[] encbuff = System.Text.Encoding.UTF8.GetBytes(str);
            return Convert.ToBase64String(encbuff);
        }

        /// <summary>
        /// Base64解密
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        public static string Base64Decrypt(string str)
        {
            byte[] decbuff = Convert.FromBase64String(str);
            return System.Text.Encoding.UTF8.GetString(decbuff);
        }
        #endregion

4、 MD5加密及驗證

MD5的加密處理應用還是比較多，由於破解難度很大，基本上大型網站或者軟體商，密碼加密一般採用這種方式居多。

而MD5可以用來獲得32、 16、8等全部部分內容加密內容，也可以獲取其加密後的雜湊值。

         /// <summary>

        /// 獲得32位的MD5加密
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string GetMD5_32(string input)
        {
            System.Security.Cryptography.MD5 md5 = System.Security.Cryptography.MD5.Create();
            byte[] data = md5.ComputeHash(System.Text.Encoding.Default.GetBytes(input));
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < data.Length; i++)
            {
                sb.Append(data[i].ToString("x2"));
            }
            return sb.ToString();
        }

        /// <summary>
        /// 獲得16位的MD5加密
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string GetMD5_16(string input)
        {
            return GetMD5_32(input).Substring(8, 16);
        }
        /// <summary>
        /// 獲得8位的MD5加密
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string GetMD5_8(string input)
        {
            return GetMD5_32(input).Substring(8, 8);
        }
        /// <summary>
        /// 獲得4位的MD5加密
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string GetMD5_4(string input)
        {
            return GetMD5_32(input).Substring(8, 4);
        }

        public static string MD5EncryptHash(String input)
        {
            MD5 md5 = new MD5CryptoServiceProvider();
            //the GetBytes method returns byte array equavalent of a string
            byte[] res = md5.ComputeHash(Encoding.Default.GetBytes(input), 0, input.Length);
            char[] temp = new char[res.Length];
            //copy to a char array which can be passed to a String constructor
            Array.Copy(res, temp, res.Length);
            //return the result as a string
            return new String(temp);
        }

5、 對檔案新增MD5標籤及驗證

這種方式比較有趣，我也是最近才發現其中的奧妙，其實我們為了防止檔案被修改，可以採用這種方式預先新增MD5碼，然後在程式程式碼中進行驗證，這樣至少可以減少部分篡改的行為吧，因為只要檔案有些少的修改，Md5碼將會發生變化的，呵呵。

         #region MD5簽名驗證

        /// <summary>
        /// 對給定檔案路徑的檔案加上標籤
        /// </summary>
        /// <param name="path">要加密的檔案的路徑</param>
        /// <returns>標籤的值</returns>
        public static bool AddMD5(string path)
        {
            bool IsNeed = true;

            if (CheckMD5(path))                                  //已進行MD5處理
                IsNeed = false;

            try
            {
                FileStream fsread = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
                byte[] md5File = new byte[fsread.Length];
                fsread.Read(md5File, 0, (int)fsread.Length);                               // 將檔案流讀取到Buffer中
                fsread.Close();

                if (IsNeed)
                {
                    string result = MD5Buffer(md5File, 0, md5File.Length);             // 對Buffer中的位元組內容算MD5
                    byte[] md5 = System.Text.Encoding.ASCII.GetBytes(result);       // 將字串轉換成位元組陣列以便寫人到檔案中
                    FileStream fsWrite = new FileStream(path, FileMode.Open, FileAccess.ReadWrite);
                    fsWrite.Write(md5File, 0, md5File.Length);                               // 將檔案，MD5值 重新寫入到檔案中。
                    fsWrite.Write(md5, 0, md5.Length);
                    fsWrite.Close();
                }
                else
                {
                    FileStream fsWrite = new FileStream(path, FileMode.Open, FileAccess.ReadWrite);
                    fsWrite.Write(md5File, 0, md5File.Length);
                    fsWrite.Close();
                }
            }
            catch
            {
                return false;
            }

            return true;
        }

        /// <summary>
        /// 對給定路徑的檔案進行驗證
        /// </summary>
        /// <param name="path"></param>
        /// <returns>是否加了標籤或是否標籤值與內容值一致</returns>
        public static bool CheckMD5(string path)
        {
            try
            {
                FileStream get_file = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
                byte[] md5File = new byte[get_file.Length];                                      // 讀入檔案
                get_file.Read(md5File, 0, (int)get_file.Length);
                get_file.Close();

                string result = MD5Buffer(md5File, 0, md5File.Length - 32);             // 對檔案除最後32位以外的位元組計算MD5，這個32是因為標籤位為32位。
                string md5 = System.Text.Encoding.ASCII.GetString(md5File, md5File.Length - 32, 32);   //讀取檔案最後32位，其中儲存的就是MD5值
                return result == md5;
            }
            catch
            {
                return false;
            }
        }

        /// <summary>
        /// 計算檔案的MD5值
        /// </summary>
        /// <param name="MD5File">MD5簽名檔案字元陣列</param>
        /// <param name="index">計算起始位置</param>
        /// <param name="count">計算終止位置</param>
        /// <returns>計算結果</returns>
        private static string MD5Buffer(byte[] MD5File, int index, int count)
        {
            System.Security.Cryptography.MD5CryptoServiceProvider get_md5 = new System.Security.Cryptography.MD5CryptoServiceProvider();
            byte[] hash_byte = get_md5.ComputeHash(MD5File, index, count);
            string result = System.BitConverter.ToString(hash_byte);

            result = result.Replace("-", "");
            return result;
        }
        #endregion

6、 SHA256加密演算法

         /// <summary>

        /// SHA256函式
        /// </summary>
        /// <param name="str">原始字串</param>
        /// <returns>SHA256結果(返回長度為44位元組的字串)</returns>
        public static string SHA256(string str)
        {
            byte[] SHA256Data = Encoding.UTF8.GetBytes(str);
            SHA256Managed Sha256 = new SHA256Managed();
            byte[] Result = Sha256.ComputeHash(SHA256Data);
            return Convert.ToBase64String(Result);  //返回長度為44位元組的字串
        }

7、 MD5及Base64結合加密

這種結合方式也是比較不錯的演算法，至少是四不像，一般分析比較困難，比較有迷惑性，就是掛羊頭，賣狗肉的行為，其實Base64加密方式，也可以做的比較複雜，不一定是上面的那種解決方式的，你可以新增一些較為複雜的演算法在裡面的。

         /// <summary>

        /// 加密字串
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string EncryptString(string input)
        {
            return MD5Util.AddMD5Profix(Base64Util.Encrypt(MD5Util.AddMD5Profix(input)));
            //return Base64.Encrypt(MD5.AddMD5Profix(Base64.Encrypt(input)));
        }

        /// <summary>
        /// 解密加過密的字串
        /// </summary>
        /// <param name="input"></param>
        /// <param name="throwException">解密失敗是否拋異常</param>
        /// <returns></returns>
        public static string DecryptString(string input, bool throwException)
        {
            string res = "";
            try
            {
                res = input;// Base64.Decrypt(input);
                if (MD5Util.ValidateValue(res))
                {
                    return MD5Util.RemoveMD5Profix(Base64Util.Decrypt(MD5Util.RemoveMD5Profix(res)));
                }
                else
                {
                    throw new Exception("字串無法轉換成功！");
                }
            }
            catch
            {
                if (throwException)
                {
                    throw;
                }
                else
                {
                    return "";
                }
            }
        }

//-----------下面是MD5Util下面的函式

        /// <summary>
        /// 新增MD5的字首，便於檢查有無篡改
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string AddMD5Profix(string input)
        {
            return GetMD5_4(input) + input;
        }
        /// <summary>
        /// 移除MD5的字首
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string RemoveMD5Profix(string input)
        {
            return input.Substring(4);
        }
        /// <summary>
        /// 驗證MD5字首處理的字串有無被篡改
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static bool ValidateValue(string input)
        {
            bool res = false;
            if (input.Length >= 4)
            {
                string tmp = input.Substring(4);
                if (input.Substring(0, 4) == GetMD5_4(tmp))
                {
                    res = true;
                }
            }
            return res;
        }

 如下面程式碼就是上面提到的Base64Util中的內容，好像演算法處理還是比較麻煩，也貼出來大家研讀一下吧。

    /// <summary>
    /// 基於Base64的加密編碼，
    /// 可以設定不同的密碼錶來獲取不同的編碼合解碼
    /// </summary>
    public class Base64Util
    {
        public Base64Util()
        {
            this.InitDict();
        }

        protected static Base64Util s_b64 = new Base64Util();

        /// <summary>
        /// 使用預設的密碼錶加密字串
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string Encrypt(string input)
        {
            return s_b64.Encode(input);
        }
        /// <summary>
        /// 使用預設的密碼錶解密字串
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string Decrypt(string input)
        {
            return s_b64.Decode(input);
        }

        /// <summary>
        /// 獲取具有標準的Base64密碼錶的加密類
        /// </summary>
        /// <returns></returns>
        public static Base64Util GetStandardBase64()
        {
            Base64Util b64 = new Base64Util();
            b64.Pad = "=";
            b64.CodeTable = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
            return b64;
        }

        protected string m_codeTable = @"ABCDEFGHIJKLMNOPQRSTUVWXYZbacdefghijklmnopqrstu_wxyz0123456789*-";
        protected string m_pad = "v";
        protected Dictionary<int, char> m_t1 = new Dictionary<int, char>();
        protected Dictionary<char, int> m_t2 = new Dictionary<char, int>();

        /// <summary>
        /// 密碼錶
        /// </summary>
        public string CodeTable
        {
            get { return m_codeTable; }
            set
            {
                if (value == null)
                {
                    throw new Exception("密碼錶不能為null");
                }
                else if (value.Length < 64)
                {
                    throw new Exception("密碼錶長度必須至少為64");
                }
                else
                {
                    this.ValidateRepeat(value);
                    this.ValidateEqualPad(value, m_pad);
                    m_codeTable = value;
                    this.InitDict();
                }
            }
        }
        /// <summary>
        /// 補碼
        /// </summary>
        public string Pad
        {
            get { return m_pad; }
            set
            {
                if (value == null)
                {
                    throw new Exception("密碼錶的補碼不能為null");
                }
                else if (value.Length != 1)
                {
                    throw new Exception("密碼錶的補碼長度必須為1");
                }
                else
                {
                    this.ValidateEqualPad(m_codeTable, value);
                    m_pad = value;
                    this.InitDict();
                }
            }
        }

        /// <summary>
        /// 返回編碼後的字串
        /// </summary>
        /// <param name="source"></param>
        /// <returns></returns>
        public string Encode(string source)
        {
            if (source == null || source == "")
            {
                return "";
            }
            else
            {
                StringBuilder sb = new StringBuilder();
                byte[] tmp = System.Text.UTF8Encoding.UTF8.GetBytes(source);
                int remain = tmp.Length % 3;
                int patch = 3 - remain;
                if (remain != 0)
                {
                    Array.Resize(ref tmp, tmp.Length + patch);
                }
                int cnt = (int)Math.Ceiling(tmp.Length * 1.0 / 3);
                for (int i = 0; i < cnt; i++)
                {
                    sb.Append(this.EncodeUnit(tmp[i * 3], tmp[i * 3 + 1], tmp[i * 3 + 2]));
                }
                if (remain != 0)
                {
                    sb.Remove(sb.Length - patch, patch);
                    for (int i = 0; i < patch; i++)
                    {
                        sb.Append(m_pad);
                    }
                }
                return sb.ToString();
            }

        }
        protected string EncodeUnit(params byte[] unit)
        {
            int[] obj = new int[4];
            obj[0] = (unit[0] & 0xfc) >> 2;
            obj[1] = ((unit[0] & 0x03) << 4) + ((unit[1] & 0xf0) >> 4);
            obj[2] = ((unit[1] & 0x0f) << 2) + ((unit[2] & 0xc0) >> 6);
            obj[3] = unit[2] & 0x3f;
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < obj.Length; i++)
            {
                sb.Append(this.GetEC((int)obj[i]));
            }
            return sb.ToString();
        }
        protected char GetEC(int code)
        {
            return m_t1[code];//m_codeTable[code];
        }

        /// <summary>
        /// 獲得解碼字串
        /// </summary>
        /// <param name="source"></param>
        /// <returns></returns>
        public string Decode(string source)
        {
            if (source == null || source == "")
            {
                return "";
            }
            else
            {
                List<byte> list = new List<byte>();
                char[] tmp = source.ToCharArray();
                int remain = tmp.Length % 4;
                if (remain != 0)
                {
                    Array.Resize(ref tmp, tmp.Length - remain);
                }
                int patch = source.IndexOf(m_pad);
                if (patch != -1)
                {
                    patch = source.Length - patch;
                }
                int cnt = tmp.Length / 4;
                for (int i = 0; i < cnt; i++)
                {
                    this.DecodeUnit(list, tmp[i * 4], tmp[i * 4 + 1], tmp[i * 4 + 2], tmp[i * 4 + 3]);
                }
                for (int i = 0; i < patch; i++)
                {
                    list.RemoveAt(list.Count - 1);
                }
                return System.Text.Encoding.UTF8.GetString(list.ToArray());
            }
        }
        protected void DecodeUnit(List<byte> byteArr, params char[] chArray)
        {
            int[] res = new int[3];
            byte[] unit = new byte[chArray.Length];
            for (int i = 0; i < chArray.Length; i++)
            {
                unit[i] = this.FindChar(chArray[i]);
            }
            res[0] = (unit[0] << 2) + ((unit[1] & 0x30) >> 4);
            res[1] = ((unit[1] & 0xf) << 4) + ((unit[2] & 0x3c) >> 2);
            res[2] = ((unit[2] & 0x3) << 6) + unit[3];
            for (int i = 0; i < res.Length; i++)
            {
                byteArr.Add((byte)res[i]);
            }
        }
        protected byte FindChar(char ch)
        {
            int pos = m_t2[ch];//m_codeTable.IndexOf(ch);
            return (byte)pos;
        }

        /// <summary>
        /// 初始化雙向哈西字典
        /// </summary>
        protected void InitDict()
        {
            m_t1.Clear();
            m_t2.Clear();
            m_t2.Add(m_pad[0], -1);
            for (int i = 0; i < m_codeTable.Length; i++)
            {
                m_t1.Add(i, m_codeTable[i]);
                m_t2.Add(m_codeTable[i], i);
            }
        }
        /// <summary>
        /// 檢查字串中的字元是否有重複
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        protected void ValidateRepeat(string input)
        {
            for (int i = 0; i < input.Length; i++)
            {
                if (input.LastIndexOf(input[i]) > i)
                {
                    throw new Exception("密碼錶中含有重複字元：" + input[i]);
                }
            }
        }
        /// <summary>
        /// 檢查字串是否包含補碼字元
        /// </summary>
        /// <param name="input"></param>
        /// <param name="pad"></param>
        protected void ValidateEqualPad(string input, string pad)
        {
            if (input.IndexOf(pad) > -1)
            {
                throw new Exception("密碼錶中包含了補碼字元：" + pad);
            }
        }
    }