Specified key is not a valid size for this algorithm

Question

I have with this code:

RijndaelManaged rijndaelCipher = new RijndaelManaged();

            // Set key and IV
            rijndaelCipher.Key = Convert.FromBa         


        

Answer 1

I don't know the length of rijndaelCipher.Key if it is 24, then rijndaelCipher.Key = s.SubString(0, 24);

So easy.