AES加密算法，如何指定返回加密后的密文字节数组大小为16,默认是32的?

Question

//默认密钥向量 
        private static byte[] _key1 = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF, 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };        /// <summary>
        /// AES加密算法
        /// </summary>
        /// <param name="plainText">明文字符串</param>
        /// <param name="strKey">密钥</param>
        /// <returns>返回加密后的密文字节数组</returns>
        public static byte[] AESEncrypt(string plainText, string strKey)
        {
            //分组加密算法
            SymmetricAlgorithm des = Rijndael.Create();           
            byte[] inputByteArray = Encoding.UTF8.GetBytes(plainText);//得到需要加密的字节数组
            //设置密钥及密钥向量
            des.Key = Encoding.UTF8.GetBytes(strKey);
            des.IV = _key1;
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);
      //      cs.SetLength(16);
            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();
            byte[] cipherBytes = ms.ToArray();//得到加密后的字节数组
            cs.Close();
            ms.Close();
            return cipherBytes;
        }