c# - RijndaelManaged - 设置 KeySize 属性有什么作用？

Question

鉴于我将 KeySize 设置为 192，当我通过执行以下操作加密一些数据时:

 static void Main()
        {
            var querystrings = "dataToEncrypt";
            byte[] keyvalue = new byte[] { 241, 205, 121, 123, 109, 246, 247, 103, 31, 225, 167, 220, 247, 119, 247, 119, 78, 125, 127, 167, 156, 213, 230, 250, };
            byte[] ivvalue = new byte[] { 194, 177, 79, 213, 87, 46, 213, 189, 243, 169, 32, 13, 217, 62, 34, 170, };
            byte[] querystringBytes = Encoding.UTF8.GetBytes(querystrings);

            using (RijndaelManaged rijndaelManaged = new RijndaelManaged())
            {
                rijndaelManaged.BlockSize = 128;
                rijndaelManaged.KeySize = 192;
                rijndaelManaged.IV = ivvalue;
                rijndaelManaged.Key = keyvalue;
                rijndaelManaged.Padding = PaddingMode.PKCS7;
                rijndaelManaged.Mode = CipherMode.CBC;

                using (MemoryStream memoryStream = new MemoryStream())
                {
                    ICryptoTransform transform = rijndaelManaged.CreateEncryptor();
                    using (CryptoStream cryptoStream = new CryptoStream(memoryStream, transform, CryptoStreamMode.Write))
                    {
                        cryptoStream.Write(querystringBytes, 0, querystringBytes.Length);
                        cryptoStream.FlushFinalBlock();
                        var output = Convert.ToBase64String(memoryStream.ToArray());
                        Console.WriteLine($"{output}");
                        Console.ReadKey();
                    }
                }
            }
        }

数据按照我的预期加密，因为 IV 和加密 key 分别长 128 位和 192 位。但是，如果我将加密 key 设置为 128 位长(为了参数起见，让我们使用与 IV 相同的字节数组)即

 static void Main()
        {
            var querystrings = "dataToEncrypt";
            byte[] keyvalue = new byte[] { 194, 177, 79, 213, 87, 46, 213, 189, 243, 169, 32, 13, 217, 62, 34, 170, };
            byte[] ivvalue = new byte[] { 194, 177, 79, 213, 87, 46, 213, 189, 243, 169, 32, 13, 217, 62, 34, 170, };
            byte[] querystringBytes = Encoding.UTF8.GetBytes(querystrings);

            using (RijndaelManaged rijndaelManaged = new RijndaelManaged())
            {
                rijndaelManaged.BlockSize = 128;
                rijndaelManaged.KeySize = 192;
                rijndaelManaged.IV = ivvalue;
                rijndaelManaged.Key = keyvalue;
                rijndaelManaged.Padding = PaddingMode.PKCS7;
                rijndaelManaged.Mode = CipherMode.CBC;

                using (MemoryStream memoryStream = new MemoryStream())
                {
                    ICryptoTransform transform = rijndaelManaged.CreateEncryptor();
                    using (CryptoStream cryptoStream = new CryptoStream(memoryStream, transform, CryptoStreamMode.Write))
                    {
                        cryptoStream.Write(querystringBytes, 0, querystringBytes.Length);
                        cryptoStream.FlushFinalBlock();
                        var output = Convert.ToBase64String(memoryStream.ToArray());
                        Console.WriteLine($"{output}");
                        Console.ReadKey();
                    }
                }
            }
        }

这仍然会毫无异常(exception)地进行加密。我的问题是:

当我明确将 KeySize 设置为 192 时，KeySize 在接受 128 位加密 key 时在内部做什么？为什么没有异常发生？

Answer 1

Key和 KeySize RijndaelManaged 类的属性继承自基类 SymmetricAlgorithm类(class)。这些属性的精确行为在 MSDN 库中没有详细记录，但如果您查看 SymmetricAlgorithm source code ，您会看到 Key 和 KeySize 属性相互交互，如下所示:

• 设置 Key 属性时，KeySize 属性会自动设置为新 key 的长度(以位为单位)。
• 当您设置 KeySize 属性时，现有的 Key 将被清除(并在下次访问 Key 时自动生成一个新的随 secret 钥)。

因此，如果您要设置 Key 属性，则事先设置 KeySize 属性没有意义。