C#中的AES 256位加密密钥大小问题

我正在尝试在C#中执行AES 256位CBC加密.我正在使用此页面上的示例密钥/iv字符串:

I am trying to perform AES 256-bit CBC encryption in C#. I am using the sample key/iv strings from this page: http://pic.dhe.ibm.com/infocenter/initiate/v9r5/topic/com.ibm.einstall.doc/topics/t_einstall_GenerateAESkey.html

但是，当我运行下面的函数时，我收到一条错误消息:指定的密钥对于该算法而言不是有效的大小."尝试设置cipher.Key时.我可以在node.js项目中使用此键/iv组合，但是我尝试将其移植到C#都无济于事.我在下面做什么错了?

However when I run the function below, I receive an error saying "Specified key is not a valid size for this algorithm." when attempting to set cipher.Key. I am able to use this key/iv combination in a node.js project, but I am attempting to port it to C# to no avail. What am I doing wrong below?

    static void Main(string[] args)
    {
        string keyString = "B374A26A71490437AA024E4FADD5B497FDFF1A8EA6FF12F6FB65AF2720B59CCF";
        string ivString = "7E892875A52C59A3B588306B13C31FBD";

        byte[] key = Encoding.UTF8.GetBytes(keyString);
        byte[] iv = Encoding.UTF8.GetBytes(ivString);

        Console.WriteLine("Key is " + key.Length + " bytes.");

        using (RijndaelManaged cipher = new RijndaelManaged())
        {
            cipher.Mode = CipherMode.CBC;
            cipher.KeySize = 256;
            cipher.BlockSize = 128;
            cipher.Key = key;
            cipher.IV = iv;

            // Create a decrytor to perform the stream transform.
            ICryptoTransform encryptor = cipher.CreateEncryptor(cipher.Key, cipher.IV);
        }

        Console.WriteLine("Success!");
        Console.ReadKey();
    }