/// <summary>
        /// 加密檔案隨機數生成
        /// </summary>
        private static RandomNumberGenerator rand = new RNGCryptoServiceProvider();
        private const int BUFFER_SIZE = 128 * 1024;
        private const ulong FC_TAG = 0xFC010203040506CF;
        /// <summary>
        /// 生成指定長度的隨機Byte陣列
        /// </summary>
        /// <param name="count">Byte陣列長度</param>
        /// <returns>隨機Byte陣列</returns>
        private static byte[] GenerateRandomBytes(int count)
        {
            byte[] bytes = new byte[count];
            //產生隨機序列
            rand.GetBytes(bytes);
            return bytes;
        }
        /// <summary>
        /// 建立Rijndael SymmetricAlgorithm
        /// </summary>
        /// <param name="password">密碼</param>
        /// <param name="salt"></param>
        /// <returns>加密物件</returns>
        private static SymmetricAlgorithm CreateRijndael(string password, byte[] salt)
        {
            PasswordDeriveBytes pdb = new PasswordDeriveBytes(password, salt, "SHA256", 1000);

            SymmetricAlgorithm sma = Rijndael.Create();
            sma.KeySize = 256;
            sma.Key = pdb.GetBytes(16);
            sma.Padding = PaddingMode.PKCS7;
            return sma;
        }
        public static void EncryptFile(string inFile, string outFile, string password)
        {
            using (FileStream fin = File.OpenRead(inFile),
                fout = File.OpenWrite(outFile))
            {
                long lSize = fin.Length; // 輸入檔案長度
                int size = (int)lSize;
                byte[] bytes = new byte[BUFFER_SIZE]; // 快取
                int read = -1; // 輸入檔案讀取數量
                int value = 0;

                // 獲取IV和salt
                //金鑰salt在加密演算法中主要被設計用來防止“字典攻擊”。字典攻擊也是一種窮舉的暴力破解法。字典中會假設一定數量的密碼值，
                //攻擊者會嘗試用這些密碼來解密密文。Salt是在金鑰匯出之前在密碼末尾引入的隨機位元組，它使這類攻擊變得非常困難
                //初始化向量IV在加密演算法中起到的也是增強破解難度的作用。在加密過程中，如果遇到相同的資料塊，其加密出來的結果也一致，相對就會容易破解。
                //加密演算法在加密資料塊的時候，往往會同時使用密碼和上一個資料塊的加密結果。因為要加密的第一個資料塊顯然不存在上一個資料塊，所以這個初始化向量就是被設計用來當作初始資料塊的加密結果。
                byte[] IV = GenerateRandomBytes(16);
                byte[] salt = GenerateRandomBytes(16);

                // 建立加密物件
                SymmetricAlgorithm sma = CreateRijndael(password, salt);
                sma.IV = IV;

                // 在輸出檔案開始部分寫入IV和salt
                fout.Write(IV, 0, IV.Length);
                fout.Write(salt, 0, salt.Length);

                // 建立雜湊加密
                HashAlgorithm hasher = SHA256.Create();
                  //     定義將資料流連結到加密轉換的流。
                using (CryptoStream cout = new CryptoStream(fout, sma.CreateEncryptor(), CryptoStreamMode.Write),
                    chash = new CryptoStream(Stream.Null, hasher, CryptoStreamMode.Write))
                {
                    BinaryWriter bw = new BinaryWriter(cout);
                    bw.Write(lSize);

                    bw.Write(FC_TAG);

                    // 讀寫位元組塊到加密流緩衝區
                    while ((read = fin.Read(bytes, 0, bytes.Length)) != 0)
                    {
                        cout.Write(bytes, 0, read);
                        chash.Write(bytes, 0, read);
                        value += read;
                    }
                    // 關閉加密流
                    chash.Flush();
                    chash.Close();

                    // 讀取雜湊
                    //在 chash 獲取雜湊金鑰
                   byte[] hash = hasher.Hash;
                   
                    // 輸入檔案寫入雜湊
                    cout.Write(hash, 0, hash.Length);

                    // 關閉檔案流
                    cout.Flush();
                    cout.Close();
                }
            }
        }
        /// <summary>
        /// 解密檔案
        /// </summary>
        /// <param name="inFile">待解密檔案</param>
        /// <param name="outFile">解密後輸出檔案</param>
        /// <param name="password">解密密碼</param>
        public static void DecryptFile(string inFile, string outFile, string password)
        {
            // 建立開啟檔案流
            using (FileStream fin = File.OpenRead(inFile),
                fout = File.OpenWrite(outFile))
            {
                int size = (int)fin.Length;
                byte[] bytes = new byte[BUFFER_SIZE];
                int read = -1;
                int value = 0;
                int outValue = 0;

                byte[] IV = new byte[16];
                fin.Read(IV, 0, 16);
                byte[] salt = new byte[16];
                fin.Read(salt, 0, 16);

                SymmetricAlgorithm sma = CreateRijndael(password, salt);
                sma.IV = IV;

                value = 32;
                long lSize = -1;

                // 建立雜湊物件, 校驗檔案
                HashAlgorithm hasher = SHA256.Create();

                using (CryptoStream cin = new CryptoStream(fin, sma.CreateDecryptor(), CryptoStreamMode.Read),
                    chash = new CryptoStream(Stream.Null, hasher, CryptoStreamMode.Write))
                {
                    // 讀取檔案長度
                    BinaryReader br = new BinaryReader(cin);
                    lSize = br.ReadInt64();
                    ulong tag = br.ReadUInt64();

                    if (FC_TAG != tag)
                        throw new Exception("檔案被破壞");

                    long numReads = lSize / BUFFER_SIZE;

                    long slack = (long)lSize % BUFFER_SIZE;

                    for (int i = 0; i < numReads; ++i)
                    {
                        read = cin.Read(bytes, 0, bytes.Length);
                        fout.Write(bytes, 0, read);
                        chash.Write(bytes, 0, read);
                        value += read;
                        outValue += read;
                    }

                    if (slack > 0)
                    {
                        read = cin.Read(bytes, 0, (int)slack);
                        fout.Write(bytes, 0, read);
                        chash.Write(bytes, 0, read);
                        value += read;
                        outValue += read;
                    }

                    chash.Flush();
                    chash.Close();

                    fout.Flush();
                    fout.Close();

                    byte[] curHash = hasher.Hash;

                    // 獲取比較和舊的雜湊物件
                    byte[] oldHash = new byte[hasher.HashSize / 8];
                    read = cin.Read(oldHash, 0, oldHash.Length);
                    if ((oldHash.Length != read) || (!CheckByteArrays(oldHash, curHash)))
                        throw new Exception("檔案被破壞");
                }

                if (outValue != lSize)
                    throw new Exception("檔案大小不匹配");
            }
        }
        /// <summary>
        /// 檢驗兩個Byte陣列是否相同
        /// </summary>
        /// <param name="b1">Byte陣列</param>
        /// <param name="b2">Byte陣列</param>
        /// <returns>true－相等</returns>
        private static bool CheckByteArrays(byte[] b1, byte[] b2)
        {
            if (b1.Length == b2.Length)
            {
                for (int i = 0; i < b1.Length; ++i)
                {
                    if (b1[i] != b2[i])
                        return false;
                }
                return true;
            }
            return false;
        }