AES解密中FlushFinalBlock遇到的错误 解决方案 和疑问

我想using System.Security.Cryptography;实现AES的加密解密功能，加密可以正常进行

解密时红色地方的语句会出现异常。

 

 

如果算法用的DES就没这个问题，请问这个异常怎么解决，微软官方上都没解决方案，国外一些提问网站也没解决。不知道谁能告诉我怎么做

 

 //AES加密
        public static string EnAES(string str, string encryptKey, string encryptVector)
        {

            int keySize = encryptKey.Length * 8;
            AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
            if (aes.ValidKeySize(keySize) == false)
            {
                keySize = Convert.ToInt32(aes.LegalKeySizes[0].MaxSize);
                if (keySize / 8 > encryptKey.Length)
                    encryptKey = encryptKey.PadRight(keySize / 8, '0');
                else
                    encryptKey = encryptKey.Substring(0, keySize / 8);
            }
            if (aes.BlockSize / 8 > encryptVector.Length)
                encryptVector = encryptVector.PadRight(aes.BlockSize / 8, '0');
            else
                encryptVector = encryptVector.Substring(0, aes.BlockSize / 8);

            byte[] key = Encoding.ASCII.GetBytes(encryptKey);
            byte[] data = Encoding.Unicode.GetBytes(str);
            byte[] vector = Encoding.ASCII.GetBytes(encryptVector);
            System.IO.MemoryStream MStream = new System.IO.MemoryStream();
            CryptoStream CStream = new CryptoStream(MStream, aes.CreateEncryptor(key, vector), CryptoStreamMode.Write);
            CStream.Write(data, 0, data.Length);
            CStream.FlushFinalBlock();
            return Convert.ToBase64String(MStream.ToArray());
        }

        //AES解密
        public static string DeAES(string str, string encryptKey, string encryptVector)
        {
            int keySize = encryptKey.Length * 8;
            AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
            if (aes.ValidKeySize(keySize) == false)
            {
                keySize = Convert.ToInt32(aes.LegalKeySizes[0].MaxSize);
                if (keySize / 8 > encryptKey.Length)
                    encryptKey = encryptKey.PadRight(keySize / 8, '0');
                else
                    encryptKey = encryptKey.Substring(0, keySize / 8);
            }
            if (aes.BlockSize / 8 > encryptVector.Length)
                encryptVector = encryptVector.PadRight(aes.BlockSize / 8, '0');
            else
                encryptVector = encryptVector.Substring(0, aes.BlockSize / 8);
            byte[] key = Encoding.ASCII.GetBytes(encryptKey);
            byte[] data = Encoding.Unicode.GetBytes(str);
            byte[] vector = Encoding.ASCII.GetBytes(encryptVector);

 

 

 

            System.IO.MemoryStream MStream = new System.IO.MemoryStream(data.Length+256);
            CryptoStream CStream = new CryptoStream(MStream, aes.CreateDecryptor(key, vector), CryptoStreamMode.Write);

            CStream.Write(data, 0, data.Length);
            //出exception的语句
            CStream.FlushFinalBlock();

            return Convert.ToBase64String(MStream.ToArray());
        }

 

 

但是下面的代码能够成功

public static string Decrypt(string toDecrypt)
        {
            byte[] keyArray = UTF8Encoding.UTF8.GetBytes("12345678901234567890123456789012");
            byte[] toEncryptArray = Convert.FromBase64String(toDecrypt);
            RijndaelManaged rDel = new RijndaelManaged();
            rDel.Key = keyArray;
            rDel.Mode = CipherMode.ECB;
            rDel.Padding = PaddingMode.PKCS7;
            ICryptoTransform cTransform = rDel.CreateDecryptor();
            byte[] resultArray = cTransform.TransformFinalBlock(toEncryptArray, 0, toEncryptArray.Length);
            return UTF8Encoding.UTF8.GetString(resultArray);
        }

        public static string Encrypt(string toEncrypt)
        {
            byte[] keyArray = UTF8Encoding.UTF8.GetBytes("12345678901234567890123456789012");
            byte[] toEncryptArray = UTF8Encoding.UTF8.GetBytes(toEncrypt);
            RijndaelManaged rDel = new RijndaelManaged();
            rDel.Key = keyArray; rDel.Mode = CipherMode.ECB; rDel.Padding = PaddingMode.PKCS7;
            ICryptoTransform cTransform = rDel.CreateEncryptor();
            byte[] resultArray = cTransform.TransformFinalBlock(toEncryptArray, 0, toEncryptArray.Length);
            return Convert.ToBase64String(resultArray, 0, resultArray.Length);
        }

 

请问可以不用下面的代码 修改第一段代码完成AES加密的任务吗？

还有我想知道问题出在哪里

我做过的尝试：

不是内存流不够大MemoryStream我试过给予很大的容量，尝试设置AesCryptoServiceProvider的padding和mode均无效。

如果第一段的代码的AesCryptoServiceProvider该做DESCryptoServiceProvider 那么代码也能运行成功。

请问问题出在哪里？