Turns out, some of the files back from Master Challenge 1 were corrupted. Restore this one file and find the flag.
We can try to scan the file for any pieces of strings, containing flag or clues for further approach.
At the end of the provided output we can see 8 file names with additional PK letters appended to it. Quick google search shows us that PK are the initals of Phil Katz, co-creator of the ZIP file format and author of PKZIP. You can read more here.
As it's not that easy to just change the file name and extract from the archive, we will have to take a closer look at the structure of the file. I'm going to use Bliss hexeditor for Linux and hexdump for navigating the hexadecimal values.
Now we can view the beginning (head) of the texthexdump.
We can clearly see the cause of the problem. Every file starts with the file signature, but this one has been overwritten with X characters. We can even view this error while trying to unzip this file.
Let's repair this with correct signature, which is 50 4B 03 04 00 00.
We have everything for the last step - zip -F which will try to somehow repair the file.