The input 'plaintext' could be binary data or other information that the attacker cannot predict.
What they can predict if they find some code interfacing with this encrypted file is the way it has been stored. It's not much of a long shot to say that if you can identify that it's just a plain zipped file then you're job will be much easier when it comes to reverse engineering this.
That being said, it's still a huge pain in the ass to work with that stuff. I mean, the US government hires some of the worlds best crypto people in the world and they still are sent for a run some times.
What they can predict if they find some code interfacing with this encrypted file is the way it has been stored. It's not much of a long shot to say that if you can identify that it's just a plain zipped file then you're job will be much easier when it comes to reverse engineering this.
That being said, it's still a huge pain in the ass to work with that stuff. I mean, the US government hires some of the worlds best crypto people in the world and they still are sent for a run some times.