RijndaelManaged - What does setting the KeySize property do?

Question

Given that I set KeySize to 192 when I encrypt some data by doing the following:

 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();
                    }
                }
            }
        }

The data is encrypted as I expected, since the IV and encryption key are 128 bits and 192 bits respectively. If, however, I set the encryption key to 128 bits (for argument's sake, you can use the same byte array as IV) i.e.

 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();
                    }
                }
            }
        }

It will still be encrypted without exception. My question is:

What does KeySize do internally since it accepts a 128-bit encryption key when I explicitly set KeySize as 192? Why is no exception raised?

Answer 1

Key KeySize RijndaelManaged SymmetricAlgorithm. MSDN, SymmetricAlgorithm, , Key KeySize :

• Key, KeySize .
• KeySize, ( ).

, Key, KeySize.