Celebrity, you need to do some research on AES-256-CBC encryption. Research how long the iv and key are. Also you need to research the jpeg file format. The instructions indicate that the jpeg marker 0xff?? is not part of the iv or key. If you are getting the error that flag.enc can't be opened for reading, then you haven't found the encrypted flag yet. You have to extract flag.enc from the jpeg before you can decrypt it.
How to extract flag.enc? I tried to use strings(command) and i found base64 code, there was openssl command and this "CmmtaSHhAsK9pLMepyFDl37UTXQT0CMltZk7+4Kaa1svo5vqb6JuczUqQGFJYiycY". I also tried to rename the file to "flag.enc", then i saw "flag" file(it was empty, 0 bytes). What way should I go? Sorry for my bad English.
Celebrity, my challenges are designed to get more difficult as the number of Challenge points increase. You may want to solve some lower point challenges before this one, because the skills you learn on lower point challenges are used again for the higher point challenges.